Reagan acts to aid steel, farms.

President Reagan is attempting to come to grips with farmers' biggest concern. ''Interest rates,'' says Harry Kravig, an eastern Colorado farmer-rancher.

''Interest rates,'' agrees an agricultural professor in Utah. ''I hear that 3 to 1 over anything else.''

On Tuesday, President Reagan announced a program to ease temporarily the debt problems of financially troubled farmers. Under the program, the Farmers Home Administration (FmHA) will consider giving farmers a five-year deferral of up to 25 percent of their FmHA loans, including interest. The federal agency will also make available $630 million in loan guarantees to private lenders. To qualify, a lender would forgive up to 10 percent of a farmer's loan but get in return a government guarantee to back up to 90 percent of the loan.

The action comes against the backdrop of wrenching economic changes in the ' 80s that have caused a crisis in American agriculture. High real interest rates have hit debt-laden farmers especially hard. One-third of all medium and large operations face serious debt problems.

But if the economics have changed for farmers, their politics have not - at least at the presidential level. Some pundits have predicted that normally Republican-leaning farmers might pin their troubles on President Reagan in this election year. Many farmers blame ballooning federal deficits for the high interest rates that are hitting debt-laden farmers.

But many agricultural observers call the administration's new program a first step toward a solution.

''I am heartened,'' says Neil Harl, an agricultural economist at Iowa State University, who has proposed a similar plan, in which lenders would forgive up to 20 percent of farmers' loans in return for federal guarantees.

The Reagan program is modest, he says. The $630 million in loan guarantees for privately financed farmers represents only about 0.3 percent of total farm debt. And for farmers with FmHA loans, he notes, the agency has some latitude in whom it will help, since the program is aimed at those it determines have a reasonable shot at financial survival.

Still, these measures may help stem criticism about the administration's insensitivity to farmers, observers say. In the farm belt, complaints about the administration's agriculture programs are common.

''Farmers in Idaho, I think, have felt the impact of the last recession severely,'' says Mike Brush, special assistant to Gov. John Evans, a Democrat. ''They're going out of business.''

One group of Idaho farmers has petitioned the governor to declare a state of disaster for one area of Idaho because of federal farm policy. Mr. Brush says the governor is seriously considering the proposal.

The administration has ''done nothing for the farmers,'' says Wayne Longtin, manager of the Mahnomen Farmers Cooperative Grain Association in Mahnomen, Minn. ''They pulled a lot more away (from farm programs) than they've put in.''

''It's kind of tough out here,'' says Don Gingerich, a beef and pork producer in Parnell, Iowa.

After meeting with Agriculture Secretary John Block and Undersecretary Frank Naylor recently, he says he senses a growing awareness of how widespread the crisis is.

Despite these criticisms, the President remains quite popular among farmers, observers say.

''I think Ronald Reagan is liked personally,'' says John Scholl, legislative liaison with the Illinois Farm Bureau. ''He has some characteristics farm-type people appreciate'' and is seen as rugged, predictable, and a strong leader.

Even farmers who complain about Reagan policies are not embracing former Vice-President Walter Mondale.

''It's a tough decision,'' says Doug Wildin, a Kansas farmer. ''But as far as choice, we don't have a choice. ... I guess the farmers in general look on (Mondale) as (representing) the past.''

Even Mr. Longtin, a Minnesota Democrat, sees trouble for Mondale in the farm belt. ''It's going to be a tough road for him.''

Although small, the farm vote is strategically planted. In a close presidential race, the farm vote is large enough that it could influence the outcome in any of about 10 states, says Dick Neubauer, director of political education at the American Farm Bureau Federation. Texas, Illinois, Michigan, and Ohio - with a total of 96 of the 270 electoral votes needed to win - are the biggest prizes.

With Mr. Mondale making little apparent headway with farmers, political analysts are paying closer attention to important Senate races.

In fact, says Mr. Harl, the new White House program may be intended to help shore up support not for Reagan, but for key Republican senators, such as Charles H. Percy in Illinois and Roger W. Jepsen in Iowa.

In the very close contest in Illinois, Senator Percy is said to have the edge among the state's estimated 770,000 farm voters.

But in Iowa, where Senator Jepsen is generally considered behind Democratic challenger Rep. Tom Harkin, observers say the farm vote is a tossup.

''I can't tell,'' says Mr. Gingerich, who, besides his farming, serves as legislative chairman of the Iowa Pork Producers. ''Both men have done quite a lot for us.''