Who will still be smiling as next 2 years unfold?

By keeping the Republicans in control of the US Senate, the American public has warily re-endorsed the broad domestic agenda of Ronald Reagan.

But voters, worried by that program's potential flaws - their fears heightened by double-digit unemployment, a long-delayed economic recovery, a budget unbalanced by huge defense outlays, and an anticipated redesign of the social security program - markedly strengthened the Democrats' hand in the House of Representatives.

Thus the results of election '82 show a surprisingly sharpened, even robust competitiveness in American national politics. Wall Street apparently liked the results. The Dow-Jones average smashed through its all-time high Wednesday afternoon.

In yet another statement, voters awarded Democrats an overwhelming majority of governorships - 37 Democrats to 13 Republicans in state mansions after Tuesday's results - as if to signal a return to Democratic dominance in state and local political organizations.

None of the results - a two-dozen-seat Democratic gain in the House, a draw in the Senate despite a far greater number of Democratic seats at risk, or the 27-to-9 Democratic edge in governors races - wipe the GOP out of the running for the White House in 1984.

But Republicans' hope of a new GOP era, fed by their 1980 successes, has suffered a blow. ''The results of the election were definitely a setback to the movement toward realignment of the political parties,'' concedes Rep. Guy Vander Jagt (R) of Michigan, chairman of the National Republican Congressional Committee. As for the Republicans' 1984 White House ambitions, to which control of state political organizations is crucial, Mr. Vander Jagt says: ''We have been weakened by the loss of governorships.''

The Republicans appear to have returned to the Eisenhower and Nixon GOP mode - capable of wresting presidential leadership, but compelled to forge coalitions with Democrats in Congress.

The Republicans' 1982 losses in the House were double what the Democrats suffered in 1978 under Jimmy Carter, who was already being tagged as ineffectual. GOP losses were, in fact, double the average first midterm loss of 10 seats for the last four administrations - Dwight Eisenhower lost 15 House seats in 1954; John Kennedy, four in 1962; Richard Nixon, 10 in 1970; and Carter , 12 in 1978. The erosion of President Reagan's strength in the House approached the average loss of 29 seats in all midterm elections since World War II - elections swayed by major forces like postwar inflation, Vietnam protest, and Watergate.

To the public, the GOP House losses of two dozen seats - or about one seat in every other state - may seem of no great moment. Neither side sees it as a landslide. But it means, in effect, a nearly 50-vote swing in party voting strength. Even if some of the new Democrats will vote with Reagan, the President will have to consult more closely with the House leadership, GOP officials say.

Reagan's defense buildup will undergo ''stretchouts, delays,'' and reduced spending by at least $6 billion or $7 billion, Republicans concede. On issues like school busing and prayer, on which amendments would have to be passed, conservatives now seem blocked by a larger moderate-liberal coalition.

But the main impact in Washington is psychological. ''The impact goes beyond the loss of 25 seats,'' Vander Jagt says. ''The aura of (Reagan-GOP) invincibility has certainly been diminished. Congressmen are likely to be more independent.''

Even in the Senate, where the Republicans retained control, the narrowness of many GOP candidates' victory margins serves as a warning to members preparing for reelection in 1984. A reversal of Reagan's economic program does not seem likely. But for many Senate Republicans, political survival will dictate the kind of distancing from full support for Reagan that was widely seen in this fall's campaigns. GOP moderate incumbents - Sens. John Chaffee in Rhode Island, Robert Stafford in Vermont, David Durenberger in Minnesota, William Roth Jr. in Delaware, Lowell Weicker in Connecticut, and John Danforth in Missouri - barely escaped Democratic challenges. In 1984, Republicans will hold the majority of Senate seats at risk.

Democrats' campaign style in 1982 - far more aggressive than in 1980 - contributed greatly to their success. Even where Democrats lost, as in the Trible-Davis Senate race in Virginia, the vigor of the Democrats' 1982 campaigning made it close. The Democrats had been caught asleep in 1980, surprised by the negative advertising campaigns of groups like the National Conservative Political Action Committee.

NCPAC was clearly 1982's biggest loser. Only one of 14 NCPAC targets in 1982, Nevada's Democratic Sen. Howard W. Cannon, lost.

Some GOP House seat defeats came in places sometimes considered conservative bastions. While Rep. Paul Trible was winning his Senate seat in Virginia, three Republican House members were going down to defeat there. In North Carolina, where the GOP national party poured in money and which is Sen. Jesse Helms's home base, Democrats reversed Republican plans to pick up three to five new seats.

Democratic organization appeared to make the difference in two Southwest states, Texas and New Mexico, where Republicans had hoped to strengthen their Sunbelt foothold. In Texas, Democrat Mark White upset Gov. William Clements, a formidable campaigner and solid Reagan ally whom the White House was counting on for help in 1984. In New Mexico, Democratic Attorney General Jeff Bingaman upset Sen. Harrison Schmitt behind an energetic young team of Democratic activists in that state.

White House delight at a double California victory - George Deukmejian for governor, Pete Wilson in the Senate race against Edmund D. Brown Jr. - was somewhat offset by the earlier decision that campaigning by Reagan in his home state would more likely have hurt the party's candidates than helped them. The question of how much racial bias might have hurt the prospects of Tom Bradley, the black Democratic candidate for governor, may never be answered, political observers say. The state's likely support for a Reagan run in 1984 had never seemed in doubt.

The White House may find some comfort, too, in the apparent close victory of Illinois incumbent Gov. James Thompson, though the final count remained obscured as state election officials tried to dry out and process a final batch of Chicago ballots somehow soaked in a Midwest downpour. For Republicans, the California win offset the Texas loss among large state governorships. And holding onto Illinois would offset a GOP defeat in a close New York governor's race for a post already held by the Democrats.

This left, however, a very poor GOP showing in other Midwest governors' races. Democrats won in Ohio, Michigan, Wisconsin, Minnesota, and Nebraska, taking Republican seats. Besides Illinois, Republicans held only Iowa and South Dakota in the Plains States races.