They were as polite a group of protesters as Washington has seen.

The members of the South Dakota legislature, only two short of their full strength of 105, wide western hats in hand, walked softly on Capitol Hill.

At an afternoon-long session in a Senate hearing room, where they were addressed by big names like Agriculture Secretary John R. Block, Federal Reserve Board Chairman Paul A. Volcker, Senate Majority Leader Robert J. Dole (R-Kan.) and Senate Budget Committee Chairman Pete V. Domenici (R-N.M.), they applauded after hearing each new version of the bad news they already knew. They even gave a standing ovation to Block, who bade them to be glad they would no longer be "wards of the state."

The last time rural America came to town, in 1979, it was different. The farmers rumbled in on tractors, parked on the Mall for days and clumped around town demanding that President Jimmy Carter give them 100 percent parity.

This time, they are pleading. And their message to the man in the White House -- against whom they said not a single harsh word -- was statesmanlike: They want him to balance the budget.

"They're not mad," said their leader, South Dakota's rambunctious Republican governor, William Janklow. "They're scared."

Owners of small and medium-size farms, beset by rising interest rates and falling prices, are an endangered species, and President Reagan is talking about making them "self-reliant" by cutting farm subsidies.

In South Dakota last year, 247 bankruptcies were declared. That's against 30 in 1981.

The high value of the dollar has all but forced them out of world markets. Farmers have created prodigies of productivity. Their efficiency is positively staggering, especially when compared with that of other sectors, notably defense contractors. But Reagan, for whom they voted in overwhelming numbers, is saying he's not about to bail them out. And Stockman says that they are getting what they deserved, although the farmers claim that only 10 percent of them are reaping ruin for land speculation during the good times.

White-haired Roger D. McKellips, the picture of the small town American banker -- he runs the bank in Alcester, S.D. -- says, "We are pretty discouraged. We have had droughts, hailstorms and crop failures, but we always saw light at the end of the tunnel. Now I don't see any increase in the price of our products."

The farmers, in their meek new mood, are trying to persuade the country that they are no longer a pampered minority and that the bell tolls for all in this moment of precarious national prosperity and gigantic deficits.

Says Steve Cutler of Wessington, a farmer/legislator, "We are willing to take a 5 percent cut to balance the budget as long as everybody else has to take that 5 percent cut."

Their immediate need is for emergency funds to cover the cost of spring planting. The Democrats say that the $650 million proposed by the administration is not enough. Dole told them that they should take the money and run. And Block, flashing a Howdy Doody grin, urged them to hurry home and start ploughing. In the long term, they will learn to love living without subsidies, he assured them.

They say that they can accept it all, as long as we are in it together, as long as defense and Social Security and other Reagan sacred cows get their lumps, too.

The governor told Block during the question period, which was remarkably tame in light of the anguish, "Our state will truly, truly support any politician of any party that will address the problem. We are willing to take cuts in every city town, district, location, township. But we are not willing to take more than our fair share."

The nation's governors, at their recent conference, tried to tell Reagan the same thing. They assured him that he can slash and chop at will, just as they do every year, being required by law to balance their budgets. Done fairly, it will cost him nothing.

The governors were impatient with his strategy of forcing the Democrats in Congress to make him take the knife in hand. Governors are uneasy amid the cosmic totals of the defense budget, but they understand Social Security, and they deplore his unwillingness to cut increases in the cost-of-living allowance. He told them that while he had not, strictly speaking, put the COLAs off-limits in the campaign, the Democrats would savage him if he gave way. He well remembered, he said, how in 1982 Rep. Claude Pepper (D-Fla.) ran around the country accusing him of wanting to put old people out in the snow.

The governors say they think that people are more willing to reduce the deficits than he is.

"In my first term," says Janklow, "I cut deaf people, blind people, poor children, judges, clerks and food stamps. But we treated everyone the same, and I was reelected by 79 percent. The farmers are here to say we will take our fair share of cuts to straighten out the mess we are in."