In the spread-out grainlands of his South Dakota congressional district, Rep. Tom Daschle, a 34-year-old second-term Democrat, wants to be known least of all as an alarmist. But what he hears among the Dakotan farmers when he visits their kitchens for lunch or spends the night in their homes during this congressional recess is pushing him in that direction.

The alarm is that a depression has come. It has hit his own state, where 66 percent of farmers' residual income goes for interest. And it pervades every part of agricultural America, where farm income has declined 39 percent in the past two years.

Get it clear, Daschle tells his urban colleagues in Congress when he returns to the Capitol from weekend visits to his district and finds their minds unfocused on rural America: "Agriculture is in a depression. Not a recession or a temporary downswing, but a downright bona fide depression. We have not seen a situation similar to this since 1933."

Similarities to the desperation of a half-century ago could fill a silo with statistics:

* In 1932, farm parity sank to 58 percent. Nine years ago it reached 91 percent, but now it is back to the depression level of 58 percent.

* In 1929, net farm income (in 1967 dollars) was $12 billion. The 1982 projected net farm income is $11 billion.

* The number of farmers forced off the land in the '30s was measured in the tens of thousands. In 1982, the weekly exodus is over 1,000. Farmland is declining in value for the first time in nearly 30 years.

Daschle has the politician's swift way with citing figures like these. What he doesn't have--to his credit--is the sort of political detachment by which some congressmen can become coolly aloof to the problems back home.

In his office the other afternoon, Daschle spoke of his district and the effects of the new depression on its communities. He told of farm families leaving for the cities and "small towns withering away." In May and June, when he made the rounds giving graduation addresses, "teachers would tell me that this was the last commencement their school would have, because schools are closing. In one small town, a school could accredit its senior class by having at least 14 graduates. It went out and got seven foreign students and paid for their tuition--in order to be sure the class was accredited."

Daschle said that it isn't only his district that is depressed. Throughout rural America, banks are closing, grain elevators going under, railroads deteriorating and farm machinery dealerships declaring bankruptcy. In the homes, the emotional tension of working harder and harder only to fall further and further behind is creating rises in the rates of alcoholism and child abuse. "The ramifications of what's going on right now in rural America," Daschle believes, "can't be overstated."

Among farm state congressmen, Daschle has emerged as a leader of the small independent farmer. He has organized the Congressional Farm Crisis Group, a 32-member commmittee seeking to bring relief to farmers in ways that the Reagan administration won't. In May, the bipartisan group introduced the Farm Crisis Act. The bill, whose eight provisions included such basics as loan guarantees and increased payments for taking land out of production (reduced supplies would stimulate prices) was supported in both the heartland and the Congressional Budget Office.

The Wichita Eagle-Beacon hailed the bill as "a reasonable, money-saving alternative to the farm program now in place" and the CBO estimated that over a four-year span the legislation would be about $900 million less costly than the Reagan administration's farm policies. Unexpectedly, the bill was defeated in the House Agriculture Committee, on a 21-to-21 vote. Pressure from the Reagan administration, a comforter of conglomerate farmers, reached such an intensity that three cosponsors of the bill voted against it.

To small farmers, the legislative defeat was another piece of silt washed away from what little is left of hope. How many more losses can farmers take? Not many, Daschle believes. He knows, too, as do the farmers, that the depression of 1982 has an added severity over the one of the 1930s. As the National Farmers Union has pointed out, inflation 50 years ago was about 2 percent, and interest rates 4 percent.