Neither government incentives nor the urgings of the militant American Agricultural movement are expected to stop U.S. farmers from planting large crops in the next few weeks.

Government estimates released yesterday predict a small decline of 10 million acres from last year's total 350 million acres for all crops. But farmers are expected to raise more soybeans, rice and hay. As things now stand, there will be only 2 1/2 million fewer acres of corn - a smaller cutback than the government would like.

Only wheat acreage is likely to be curtailed sharply, a development that the government had hoped for because of the large surpluses of the grain.

Department of Agriculture economist Howard Hjort said that the estimates of the growing plans of farmers do not change earlier government projections of a 6 percent to 8 percent annual increase in retail food prices.

These figures were released yesterday just as militant farmers who are in Washington to demonstrate for more government help issued new threats to curtail food productions.

Many of the farmers bitterly denounced Congress and President Carter for the overwhelming defeat of an emergency farm bill Wednesday.

Demonstrators belonging to the American Agricultural Movement had lobbied here for months, saying their costs exceed their incmes.

In Springfield, Colo., spokesman Herb Brown said yesterday: "If people want to get food, they had better start planning vegetable gardens now. It's just a hard blow for the farmers. The country doesn't think it needs us. So why shoul we produce cheap food?"

Gregg Suhler, one of the group's founders, said in Colorado that the movement would "never give up . . . we will be back again and again and again. We say to the Congress and to the president; Watch out, this is only the beginning."

On Wednesday, marchers grouped outside the White House fence, some of them shouting, "Mr. Carter, don't call yourself a farmer anymore."

Many of the farmers said they would work for the defeat of congressmen who voted against the emergency farm bill.

However, Department of Agriculture economist Howard Hjort said yesterday that "at least in the Corn Belt there is no indication of widespread participation in the American Agricultural Movement or a desire to reduce (planted) acreage beyond what the (administration) program calls for."

A government plan announced March 29 would seek to idle 10 million acres of feed grain land and 11 million acres of wheat fields, (Corn is the country's major feed grain.)

According to the survey of farmers on which yesterday's estimates were based, growers plan to reduce their plantings of the wheat used in bread by 10.2 million acres, just under what the government feels is necessary to prevent bigger surpluses and a collapse of wheat prices. However, the farmers plan to increase their growing of durum wheat used for macaroni and spaghetti.

Midwest farmers appparently are much reluctant to cut back on plans to plant corn, however. Corn prices have been rising steadily, and soil moisture is now excellent - a situation that bodies well for high yields per acre.

The administration program announced March 29 would send corn farmers voluntarily idled land a government check equal to 20 cents a bushel for their usual production on the unused land.

Hjort said it is possible that the prospect of these payments will entice more farmers to idle land as the spring planting season draws near.

The legislation defeated Wednesday would have sharply increased support prices for Wheat, feedgrains and cotton. Opponents of the measure in both parties charged that it would be strongly inflationary.