Scratch his skin just a bit and Rep. Pat Roberts (R-Kan.) oozes wheat. He talks wheat, breathes wheat, lives wheat all day long.

Then, as he leaves for home each evening, Roberts checks a big signboard on his office wall, the baleful reminder that he is the Congressman from Wheat. The board shows the daily wheat closing prices (always too low) at the Dodge City market. Wheat is that important.

Someplace else, Rep. Charles Rose (D-N.C) is worrying about what they're trying to do to peanut farmers. Steve Gunderson (R-Wis.) stiffins when they go after milk. Joe Skeen (R-N.M.) frets about the price of lamb and wool. Larry J. Hopkins (R-Ky) and Walter B. Jones (D-N.C.) never know when political lighting will strike the tobacco they cherish.

These are Excedrin days for Roberts and his friends on the House Agriculture Committee, an oddly compatible assortment of men who find themselves in a devilish predicament.

The headlines these last few weeks have gone to the Budget committees of Congress. They are setting next year's spending targets, declaring Congress' good intentions. But then will come the less puffy business of translating these good intentions into law, or not. And this will be up to committees with much different views of the world, the legislative or authorizing committees like Agriculture, the very ones that created the programs now on the chopping block.

Members vie for seats on these committees so they can help the interest groups back home; they get on the committees to vote "aye." Now they are being told by the Reagan administration and the polls that the wise thing to do may be to vote "nay" instead. They are hurting, and on no committee more than Agriculture.

The quadrennial farm bill will be the first big one of the box this year, one of the first major tests of Congress' new zeal to cut spending. The farm states, moreover, are mainly conservative in their philosophy, places where people believe good government is small government. But farming and farm states are also much subsidized by the federal government, and that is the problem.

The administration wants in various ways to reduce federal farm aid. It would cut out a program that supplements farmers' incomes when prices are low. It would increase price supports for most products only modestly.It would drop such protective devices as peanut acreage allotments. It would curtail assorted other forms of rural aid.

In the process, it is putting farm-state philosophy and farm-state congressmen to the sorest of political tests.

Some items from the early skirmishing:

The 57 counties in Roberts' western Kansas district make up the largest wheat-producing zone in the world. He and other wheat-state legislators are depressed by the proposals of President Reagan and his agriculture secretary, John R. Block, to provide only moderate help to wheat farmers.

Thomas A. Daschle (D-S.D.) represents one of the most sparsely populated districts legislators applaud the budget cuts, but they are indignant over Reagan's plans to scale down federal aid to rural electric and telephone systems.

"I would beg you to reason with us, implores Rose, speaking for himself and other peanut-state members as Block announces a major shakeup in the peanut-support program in the name of economy. (Rose's subcommittee last week quickly rejected the Block plan.)

Beryl F. Anthony Jr. (D-Ark.) and William M. Thomas (R-Calif.), fiscal conservatives from big farm areas, are bothered by the Reagan-Block move from disaster aid to crop insurance; concerned like others about export credits for foreign buyers while farmers at home get less aid, as Reagan proposes.

And so it goes, from one farm issue to another, and the sounds of displeasure will get louder as the committee keeps biting into political bullets that are liable to explode at any moment.

"We'd like to see the farm bill go to the floor in a dispassionate way, but there will be a lot of demagoguing on the budget and taxes," said a lobbyist for a major farmers' group. "If it moves quickly to the floor, most of us feel it could be made into a major Reagan policy test. We hope that doesn't occur. . . . We'd rather see the social and education programs go through before the farm bill."

There is a certain poetic irony to the probability of an early confrontation over the farm measure. In a very special way, the Agriculture committees in both the House and Senate epitomize the vested interests in Congress that Reagan avers he wants to root out. In effect, farmers own the committees.

As a result, farm-state legislators battle for seats on the committees, in fact view them as rights of inheritance. Roberts, a freshman, is an example. He muscled ahead of others and won a seat, convinced of the rightness of his claim.

"Western Kansas is the largest wheat area in the world and we traditionally have always had someone on the committee. We needed the seat, and that was the essence of my campaign," he said.

Just as a Gunderson sees his role as protecting his dairy farmers, a Rose his peanut farmers, a Hopkins his tobacco growers, Roberts sees himself as the man from wheat."I represent grain and livestock. If I don't represent my people, no one else will," he said.

And that, traditionally, is how the Agriculture Committee has been made up. Each major commodity has a defender. All Americans eat food, and presumably might care about food policy. But all Americans do not dominate the committee.

A look at a representational map points that up. New York, for example, not a key farm state, has only one member, Rep. Frederick W. Richmond (D), whose main interest has been in preserving the food-stamp program from Reagan's scythe.

North Carolina, big in tobacco and peanuts, has three members, as does Iowa, a big grain and livestock state. The top agricultural state, California, has five seats. Both of rural South Dakota's congressmen are on the committee.

The same map shows that onlyu two states north of Virginia and east of Indiana, Vermont and New York, are represented on the committee. Similar comparisons may be made with the Senate committee, now headed by Sen. Jesse A. Helms (R-N.C..).

From that decades-old farm-state hammerlock on the farm committees, even more compartmentalization by commodity has occurred on the subcommittees that make the major policy decisions affecting the rural sector.

The House wheat, soybeans and feed grains subcommittee, for instance, is chaired by Rep. Thomas S. Foley (D-Wash.), who gave up the committee chairmanship to become House majority whip. His state happens to be a major wheat producer. The subcommittee is dominated by grain-state members.

Rep. Tom Harkin (D-Iowa) heads the livestock, dairy and poultry subcommittee. Iowa is a major hog state and is among the top 10 in dairy farming. The other 13 members represent districts where those products are vital.

Look at Rose's tobacco and peanut subcommittee. North Carolinians hold the three top-ranking seats. Clint ROBERTS (R-S.D.) is the only nonpeanut or nontobacco legislator among the 10 on the subcommittee.

A recent reorganization, while retaining much of that special-interest representation, has given some broader regional flavor to most of the subcommittees.

"Peanut and tobacco is an exception, because they scramble to get on that one," said Chuck Frazier, longtime Washington representative for the National Farmers Organization. "But the parochial-type of interest in vote trading as not occurred so much lately."

Democrat Dan Glickman, one of two Kansans on the wheat subcommitte, agrees. "It is half-true that we tend to take more interest in the commodity from our area -- tobacco and sugar, for example, are not high priority for me. But there is a thread running through our committee that the plight of the producers is rather similar, and you thus find more members interested in different commodities."

The broader committee view Glickman talks about is going to sharply affect the shape of the farm bill, in the eyes of Rep. Floyd J. Fithian (D-Ind.), whose major constituencies are farmers and steelworkers.

"Thus far, I've carried water on both shoulders," Fithian said recently, "because I have as many steelworkers as farmers. But it's hard to explain why I don't want to limit automobile imports while we'll selling soybeans to Japan."

"I think I know what's best for corn and soybeans [major Hoosier crops], but I think that old single-commodity feeling on our committee may be breaking down. In the past, Floyd Fithian didn't say much about cotton or peanuts. . . . There was an understanding that you don't attack other programs -- there was, for example, always a deference to the Georgia people on peanut issues."

Fithian continued:

"Helms may be way off to the right, but you read his basic speech on agriculture and then read Tom Foley's basic speech and it's hard to discern a difference on farm programs. Agriculture policy has had to be bipartisan, because in the past you only had 150 true 'aggies' in the House. You had to come to a wide consensus."

One meaning of that, in the context of a Reagan-Congress wrestling match over farm policy, is that a Pat Roberts, loyal Republican who thinks his president is missing the point on agriculture, will find plenty of support for wheat farmers who wants target prices preserved or an interest-rate break on their grain-reserve holdings.

"The safety net the president talks about is squarely on the groud for us," Roberts said the other day. "Our hope was that with this election, we would get out of an era in which everybody was trying to play secretary of agriculture. . . . We are going to be first out of the gate with this farm bill and, politically, it is going to be tough for Ronald Reagan. The Carter-Reagan policies don't appreciate the farmers' cash-flow problems. It's very serious right now, and farmers are up against the wall."

So, the faces have changed a good deal and the House committee has undergone some change, but similar answers keep turning up for the old questions. Chairman E. (Kika) de la Garza (D-Tex.) said bluntly the other day that his committee won't buy the whole Reagan package -- it treads on too many toes.

In that aura of commodities under siege, there is still another angle. John Doyle, an agriculture analyst at the Environmental Policy Center and author of a major study on rural electric systems, touched on it as he listened to a subcommittee debate last week on Reagan's proposed changes for electric and telephone financing.

Talk that day was about an old question.Answers were similar -- that the rural sector needs the federal subsidy for its lights and communications services.

"This committee remains in its own little world," Doyle said, "still not looking at broad policy. Democrats are jumping up and defending the whole program instead of looking at it to see if rural electric can do a better job, say, just in the area of conservation, for the same buck."

"A far-seeing Democrat would admit there's abuse in this, but he would also point out that investor-owned utilities get tax subsidies that Reagan is not changing. Nobody is pointing out that rural electric co-ops are involved in at least 58 joint projects with private utilities," Doyle said. But then, this is the Agriculture Committee."