Election '84: Northeast's key races.

MASSACHUSETTS Particularly high on the GOP ''wanted'' list is the Senate seat wrested from the party's hands six years ago by Massachusetts Democrat Paul E. Tsongas. Senator Tsongas is not seeking reelection.

Thus far, however, it is uncertain who either the GOP or Democratic contenders will be: The Massachusetts congressional primary is scheduled for Sept. 18.

On the Republican side, Elliot L. Richardson, a moderate and a former US attorney general, is running against Raymond Shamie, a conservative millionaire industrialist who unsuccessfully challenged Sen. Edward M. Kennedy in 1982.

A four-way contest involving US Rep. James M. Shannon, Lt. Gov. John F. Kerry , Secretary of State Michael J. Connolly, and David M. Bartley, a former speaker of the Massachusetts House of Representatives, will decide which of these Democrats will advance to the November ballot.

Although he thoroughly supports President Reagan's reelection bid, Mr. Richardson says he ''cannot support'' the 1984 GOP platform. Mr. Shamie, who may be closer to Mr. Reagan ideologically than Richardson, says he solidly backs the platform adopted last month in Dallas. Polls indicate that Richardson holds a fairly wide lead over Shamie and also leads, though more narrowly, Messrs. Shannon and Kerry, the two Democratic front-runners.

Massachusetts' Fifth and 10th Congressional Districts also may be within the GOP's reach.

In the 10th District, comprising Cape Cod and most of the rest of the Bay State's southeastern corner, sixth-term liberal Democratic US Rep. Gerry E. Studds is fighting the battle of his political life.

Plymouth County Sheriff Peter Y. Flynn, a conservative and Mr. Studds' chief Democratic challenger, is trying to capitalize on the fact that US House colleagues censured the congressman last year for having a homosexual affair with a teenage congressional page a decade earlier.

Three Republicans, including Lewis Crampton, the party's 1978 nominee for state treasurer and more recently a high official within the US Environmental Protection Agency, are tussling for the right to take on the winner of the Democratic race.

The Republican Congressional Campaign Committee's preprimary contribution of , one of Crampton's rivals. Mr. Bennett has appealed to Reagan to help pry loose a equal sum for his candidacy.

With Representative Shannon campaigning for the Senate, Republicans are trying to regain his Fifth Congressional District seat.

This district stretches from bedroom communities west and northwest of Boston to the New Hampshire border. Until a decade ago, it had been held by Republicans for more than 50 years.

The GOP nominee is expected to be lawyer Gregory Hyatt, a conservative and a former executive director of Citizens for Limited Taxation. This group spearheaded Proposition 21/2, a 1978 statewide initiative petition drive that led to sharp cuts in property taxes.

Most of the attention on the primary battle for the Fifth District thus far, however, has been focused on Democratic contest between state Sens. Chester G. Atkins and Philip L. Shea.

Senator Shea, a conservative, has his home base in the blue-collar end of the district, including his home city of Lowell. Senator Atkins, a moderate, is state Democratic chairman and hails from Concord, a more affluent and liberal part of the district. CONNECTICUT

Democratic insiders are increasingly apprehensive about prospects for retaining the Third Congressional District seat. The contest is a rematch of the 1982 race, in which first-term incumbent Lawrence J. DeNardis lost by a narrow margin to Democrat Bruce A. Morrison. The area, which includes New Haven, is generally viewed as a swing district.

The Connecticut GOP also has its sights on the state's Fifth Congressional District. Four years ago, three-term Democrat US Rep. William R. Ratchford had a fairly close call when Reagan carried the Nutmeg State with 48.2 percent of the vote to 38.5 percent for then-President Carter. This year Representiative Ratchford's Republican contender is state Rep. John Rowland. MAINE

The brightest prospects for Democrats in New England may be in Maine's First Congressional District, where one-term incumbent John R. McKernan Jr. is pitted against state Rep. Barry Hobbins of Saco, a former Democratic state chairman. Representative McKernan won his seat two years ago by a paper-thin margin.

Republican US Sen. William S. Cohen is considered likely to be reelected despite challenges from the opposition. NEW HAMPSHIRE

Perhaps less secure may be conservative Republican US Sen. Gordon J. Humphrey of New Hampshire. He is being challenged in his bid for a second term by Democratic US Rep. Norman E. D'Amours, a fifth-term moderate from the state's First Congressional District.

Contributing, perhaps substantially, to the Humphrey candidacy could be a strong Reagan campaign presence in the Granite State, where first-term GOP Gov. John H. Sununu may also face stiff opposition in November.

New Hampshire's need for revenue is surfacing as the key issue in the Democratic gubernatorial primary. Portsmouth lawyer Paul McEachern, one of three contenders in this race in the state's Sept. 11 primary, wants to impose a state income tax. State Rep. Chris Spirou of Manchester, the state House Democratic floor leader, and lawyer and former Nashua alderman Robert DuPay oppose any such broad-based tax. Governor Sununu also opposes such a tax. VERMONT

Four-term Vermont Gov. Richard A. Snelling (R) is not seeking reelection. Former Democratic Lt. Gov. Madeleine M. Kunin, who unsuccessfully opposed Governor Snelling in 1982, is making a second try for the Green Mountain State's governorship. Her foe after the Sept. 11 GOP primary is expected to be either Vermont Attorney General John Easton or Hilton Wick, former chief executive officer of the state's largest bank. RHODE ISLAND

Four-term Democratic incumbent J. Joseph Garrahy (D) is not running for reelection. Warwich Mayor Joseph Walsh and four-term state Treasurer Anthony Solomon are vying for the Democratic gubernatorial nomination on the Sept. 11 primary ballot. Cranston Mayor Edward DiPrete has the GOP nomination salted away in the heavily Democratic ''Little Rhodey,'' the only New England state Reagan failed to carry in 1980.

Democratic US Sen. Claiborne Pell is expected to win reelection despite challenges from the opposition. NEW YORK

In New York, the Sept. 11 primary includes some important races, and voter turnout is the concern of many candidates. Traditionally, primary participation is low in this state, and campaigners are working hard to ensure that their supporters will come to the polls.

In the Ninth Congressional District, the race is on to see who will fill Democratic vice-presidential nominee Geraldine A. Ferraro's House seat. Four Democrats are vying in the primary: Gloria D'Amico, chief clerk of the Queens County Board of Election; Assembleyman Clifford E. Wilson; New York City Councilman Thomas J. Manton; and Walter H. Crowley. The GOP contenders are Salvatore Calise and Serphin R. Maltese, executive vice-chairman of the New York State Conservative Party.

Voter turnout will be key in another Queens primary race. Incumbent Rep. Joseph P. Addabbo (D), who chairs the House defense appropriations subcommittee, and Simeon Golar, a former head of the New York City Housing Authority and a family court judge, are engaged in one of the fiercest primary battles here. Mr. Golar, a black, seeks to oust the 24-year veteran the Sixth District, which is more than 50 percent black and Hispanic.

In Manhattan, Rep. Bill Green (R) is watching the outcome of a four-way primary race between Borough President Andrew Stein, Cornell University administrator Betty Lall, who did well against Mr. Green in 1982, Robert Tembeckjian, and Arnold Perey. The general election race for the 15th District could be one of the more expensive in the country this year, say observers, who point out that a Green-Stein race would match two of the richest politicians in the state.

In Westchester County, just north of New York City, three Democrats seek to replace retiring Rep. Richard L. Ottinger (D). They include Oren Teicher, an Ottinger aide, and Edward Meyer and Peter Peyser, both Republicans-turned-Democrats. The Republican candidate for the 20th District seat will be Joe DioGuardi.

Despite state pride in Ms. Ferraro's nomination, Republicans say that Reagan's popularity will help some of their congressional candidates in the general election. Mark Rivers of the state GOP headquarters lists several races that he calls winnable. These include the race in the 34th District where incumbent Democrat Stan Lundine of Jamestown will face Republican Jill Emory, wife of a former state lieutenant governor, and in the 28th District, where Rep. Matthew F. McHugh (D) is being challenged by former assembleywoman and educator Connie Cook (R).In addition, the retirement upstate of Republican Barber B. Conable Jr. means a general election race in the 30th District between W. Douglas Call (D) and Fred J. Eckert (R). NEW JERSEY

Although New Jersey's congrssional delegation has a Democratic majority - there are nine Democrats, four Republicans, and one open seat up in this election - a court-upheld Republican redistricting plan may spell danger for at least one longtime Democratic incumbent. Joseph G. Minish, first elected in 1962 , represents the 11th Congressional District, which leans Republican. His opponent, Dean A. Gallo, the State Assembly minority leader, is a Republican who is conservative on economics but more moderate on environmental and social issues. Some observers say Reagan, who won handily in the state in 1980, could offer coattails to help Mr. Gallo.

Democrats, on the other hand, hope to capture several new seats. In the 13th District, Democrat James B. Smith faces State Sen. H. James Saxton (R) in hopes of filling the seat of the late Republican Rep. Edwin B. Forsythe. Democrat James C. Hedden, a young labor organizer, takes on GOP incumbent Rep. Christopher H. Smith in the Fourth District.

Popular House incumbents like Peter W. Rodino Jr. (D), James J. Florio (D), and Mathew J. Rinaldo (R) appear likely to be reelected.

Sen. Bill Bradley (D), who is on many observers' lists as a natural for national politics, is expected to have an easy race against Mary Mochary, GOP mayor of Montclair. A recent poll by the Eagleton Institute of Politics shows Senator Bradley ahead by 65 to 11 percent. The survey also showed that less than 40 percent of New Jerseyans know Mayor Mochary, and she is having a hard time getting contributions for her uphill battle, some observers say. Without money it is hard to get known, says Cliff Zukin of Eagleton, since the two major media marketplaces, New York and Philadelphia, which cover the state, are among the most expensive in the country.

There will be two ballot measures in the November general election - a bond issue that would provide money for improved research and education and seed money for expansion of high-technology industries, and a referendum on a financial plan that would help pay off a transportation improvement program. DELAWARE

In tiny Delaware, home of chemical companies, liberal banking laws, and poultry farms, it will be a busy fall for politicians.

Voters must replace popular Republican Gov. Pierre S. (Pete) du Pont IV, who is ineligible for a third term. US Sen. Joseph R. Biden Jr. (D) and Delaware's one congressman, Thomas R. Carper (D), are up for reelection. Both members of Congress hope to retain their seats.

But before the general election gets under way, an important Sept. 8 Democratic primary is being held to determine the candidates for governor and lieutenant governor. And, according to observers, these races hinge somewhat on the voter turnout in Wilmington, where a mayoral and city council president race are hotly contested.

''That's where the vote will be heavy,'' says one Democrat. Wilmington is more than 50 percent black, and the presence of several black candidates in both the four-way mayoral and the three-way city council president races could affect who will face Republican Lt. Gov. Mike Castle. He wants to succeed Governor Du Pont. The Democratic primary will pit William T. Quillen, a former state Supreme Court justice, and Sherman W. Tribbitt, a former governor.

In the Senate race, two-term incumbent Biden faces Republican John M. Burris, a former state House majority leader. Mr. Burris has a ''long, uphill battle,'' admits Republican state chairman Jerome Herlihy, against the popular incumbent.

Elise du Pont, wife of the current governor and a former administrator at the Agency for International Development, is challenging first-term Representative Carper in a race that could be one of the most expensive in the state.

''Elise is doing well,'' says Mr. Herlihy. ''So is her opponent.'' Carper aides cite polls showing that Mrs. Du Pont began 12 to 15 points behind, and has remained at that level despite early campaigning.

In a state that weathered the recent recession better than most in the Northeast, even Democrats rate Governor Du Pont's pro-business and banking administration as ''terrific.''

With nearly one-third of Delaware voters considering themselves independent, there is not an abundance of partisan bickering. Though campaign staffs mention such issues as education, foreign policy, and blue-collar jobs, the most repeated question from the various camps is: ''Who has the ability to get things done for Delaware's future?'' PENNSYLVANIA

Jobs and unemployment are still an issue in Pennsylvania, which was hit hard during the recent recession. Candidates for Congress, statewide positions, and state House and Senate seats are busy talking about the economy.

The state is an odd political mix. Anchoring the state at the east and west are Philadelphia and Pittsburgh, both Democratic strongholds. But Pittsburgh, an industrial, almost Midwestern town, was the home of a large blue-collar defection to President Reagan in 1980. Philadelphia has a large population of poor minorities, as well as more affluent white-collar workers in the surrounding suburbs.

The middle, rural section of the state leans Republican. Both US senators and the governor are Republican. The congressional delegation is split - 13 Democratic and 10 Republican.

Both parties point to several key congressional races. The 15th District, which includes Allentown, pits Jane Wells-Schooley, a Democratic activist and a former vice-president of the National Organization for Women, against three-term GOP incumbent Don Ritter.

In the GOP-dominated Eighth District, near Philadelphia, incumbent Peter H. Kostmayer (D) faces Vietnam war veteran and Republican David Christian. Democratic Rep. Bob Edgar has been targeted by the GOP, which has put up Curt Weldon, a Delaware County councilman and former mayor of Marcus Hook, for the seat in the Seventh District. A victory for Representative Edgar is important, because he may run for the US Senate in 1986, say observers.

Democrats are eyeing the Erie-based 21st District seat of freshman Republican Tom Ridge, who won the 1982 election by 729 votes. His opponent will be James A. Young.

Statewide races include treasurer, attorney general, and auditor general. Although Republicans admit that ''unemployment and GOP stereotypes'' may hurt some races, Edie Ott of the state GOP predicts that her party will retain control of the state Senate, and several Democrats agree. But Democrats expect to keep their majority in the state House. MARYLAND

It is a quiet year in Maryland politics. There are no gubernatorial or US Senate races. Baltimore is in between mayoral campaigns. And most incumbents in the eight congressional districts seem bound for reelection.

But Republicans, who hold only one congressional seat now, have targeted two seats for the general election. Helen Delich Bentley will have her third shot at defeating 22-year House veteran Clarence D. Long (D) in the Second District. In 1982, Mrs. Bentley, who chaired the Federal Maritime Commission during the Nixon and Ford administrations, held Representative Long to less than 55 percent of the votes for the first time in his career.

''Long is not representative of the constituency there (north Baltimore suburbs),'' says Jeannette Wessel, executive director of the state GOP, who adds that Mrs. Bentley's race is getting support from both state and national Republican supporters.

A Bentley campaign aide says his candidate will question Long on foreign policy issues, and on issues directly affecting the district, such as jobs and economic programs.

Her interest in the Baltimore harbor, bolstered by her work in Washington, has translated into votes for her in past elections.

The campaign could be an expensive one. Both campaigns have estimated a budget of around $500,000.

Another contest Republicans are watching is the First District race between Democratic incumbent Roy Dyson, a four-year congressman who has voted for Reagan budget initiatives, and Republican Harlan C. Williams, a realtor.

But Mr. Dyson's reputation for constituent service will make him tough to beat, some observers say.

First of six regional campaign roundups. Staff writers George B. Merry in Boston and Victoria Irwin in New York contributed to this report.

One chart: 11-STATE REGIONAL POLITICAL PROFILE

POPULATION: 53,947,000

White 85.2%

Black 10.9%

Other 3.9%

AVERAGE 1980 TURNOUT: 56.1%

(Percent of voting-age pop.)

US REPRESENTATIVES: Democrats 66

Republicans 38

US SENATORS: Democrats 11

Republicans 11

GOVERNORSHIPS: Democrats 6

Republicans 5

TOTAL ELECTORAL VOTES: 126

Source: Statistical Abstracts