Farmers were once a powerful bloc in this country. Presidential politics was often farm politics, and The Nation magazine was moved to write in April 1953 that "farmers in the upper Midwest wheat country will decide whether Congress stays Republican or goes Democratic in 1954."

But farmers no longer command the instant response in Washington that they did in that heyday of farm power.

This week, however, the Senate and House Agriculture Committees finally approved several pieces of legislation to help farmers repay loans and add to their incomes. The proposals would go part of the way to meeting the grievances of the American Agriculture Movement, which says farm prices no longer cover farm costs and escalating farm debt.

Yet the tactics, and words, of the movement suggest a rising level of desperation in trying to get its message across to the urban majority that now controls in Congress.

Yesterday, several thousand movement members marched from the White House to the Capitol with 73 goats, 12 roosters, a couple of guinea hens and a Missouri mule to compel the attention of the lawmakers. Several goats slipped past the Capitol Police dogs brought up as reinforcements, and got as far as the anteroom of Sen. Ernest F. Hollings (D-S.C.).

But the discouragement of th demonstrators was summed up by Danny Dumey, a farmer from Oran, Mo. "Everybody where we come from survives on agriculture, but here we can't make them understand what we're talking about," he said.

Not all on Capitol Hill were unsympathetic to the display of farm rebellion.

"In the steel industry they play a round of golf at Burning Tree [country club], hit up a senator or two and what they want gets done," said a congressional aide. "The farmers who come here are a little naive. But when this many people speak they can't be all wrong."

Statistics tell part of the story why the movement so far has failed to swing Congress behind its demands for full parity for farmers.

In 1933, there were 6.6 million farms and more than one fourth of the population lived on them. The New Deal committed the government to intervenion in the agricultural economy to support food producers.

The objective was to prevent a recurrence of the wheat price collapse of the Depression years. Farmers held substantial power in Congress until well into the 1950s. But as their numbers declined, and the Supreme Court ordered a legislative reapportionment that reduced the influence of rural areas, the farm bloc's influence diminished.

Today, there are 2.7 million operating farms, inhabited by less than 4 percent of the population, according to the Department of Agriculture. And nearly half of the owners of those farms report that they derive their principal income outside their farming activities. In 1974, according to the Census Bureau, there were 530,000 farmers growing wheat, 983,000 growing corn and 539,000 raising hogs.

At the same time, the increasing specialization in American farming reduced the power of traditional farm organizations such as the American Farm Bureau Federation and the National Farmers Union.

General, diversified farmers were replaced by farmers growing particular crops, or raising livestock. The interests of these specialists often diverged. Corn producers favor high grain prices, but livestock raisers and poultrymen prefer low prices of the grain for feed, which makes up a substantial part of their overall costs.

"Farmers are atomized now - they can't organize themselves to make a significant impact, the way the coal miners can," said an official of the Department of Agriculture.

Since the early 1960s, farm lobbying has tended to form around narrow groups with interests in special commodities, such as peanuts, rice, tobacco and dairy products.

"There has been a realignment of the political forces in agriculture - into regional groups and specialists," says Prof. Phillip M. Raup of the Department of Agriculture and Applied Economics at the University of Minnesota.

In economic terms, however, farmers still account for a large bloc of national wealth. Last year, they sold more than $100 billion worth of goods out of a gross national product of $1.7 trillion. Farm production also generated more jobs and value in the processing, transportation and retailing end of the food economy.

Economiara say there is no question that certain segments - but not all - of this farm economy are now deeply troubled. Dairymen, hog raisers, and to some extent cattlemen are in fairly good condition, officials say.

Nevertheless, farm debt has risen rapidly compared with net earnings since 1974. Hardest hit are corn and wheat growers who bought high priced marginal farmland several years ago. But other groups, such as potato farmers in Maine and Idaho, are also suffering.

Potato farmers say they are adversely affected by Canadian imports.

According to Raup, land is overvalued in some parts of the country, especially in crop growning areas. Either land values will have to decline - causing additional squeezes on farmers who bought it when prices were inflated - or farm prices will have to increase soon, he said.

"Some farmers paid too much for grain land," he said. "They made a bad business decision, and how they want the rest of the country to bail them out."