President Reagan will announce next week that he will go ahead without waiting for Congress and put in place his plan to give farmers surplus grain if they agree not to plant part of their crops this year.

Reagan, agriculture sources said yesterday, will tell the American Farm Bureau Federation convention in Dallas on Tuesday that the payment-in-kind (PIK) program to help pump up the depressed farm economy will be set up without the authorizing legislation the administration sought in vain from Congress last month.

The president's appearance before the friendly, conservative Farm Bureau comes at a time when many farmers, desperate over low prices and bleak prospects for this year, are increasingly militant and demanding help from Washington.

Violence broke out twice this week in the Farm Belt over the economic situation. Farmers were tear-gassed at a Springfield, Colo., foreclosure sale on Tuesday, and in London, Ohio, yesterday, a farm protest leader facing foreclosure scuffled with a Production Credit Association official.

In another development yesterday, Agriculture Secretary John R. Block scheduled a Dallas news conference to follow Reagan's speech, presumably to outline the acreage-reduction program that is intended to prop up the sagging farm economy.

Block last month proposed payments in kind, a sharp departure from the administration's free-market philosophy, as a last-ditch effort for dealing with the huge surpluses that depressed prices, pushed net farm income in 1982 to its lowest point since 1933 and sent federal support program costs soaring. As much as half of a farmer's acreage could be retired from production this year with the payment-in-kind plan.

Participants would get surplus federal grains, rice and cotton instead of cash, which they could sell or use to feed livestock. PIK would supplement an existing acreage-reduction program, for which cash payments are made.

The House quickly gave Block the legal clearances he sought in December, but his proposal stalled when objecting senators raised questions about some specifics. PIK finally was stymied when Sen. John Melcher (D-Mont.) refused to allow the legislation to be debated at the end of the session.

Since then, Block has had Department of Agriculture attorneys studying ways the program could go ahead without the two main authorities he had sought from Congress. One would waive a limit of $50,000 on payments to individual farmers; the other would allow the USDA to dispose of surpluses at less than cost if necessary.

Meanwhile, USDA commodity and financial specialists have worked overtime this week and are on orders to continue through this weekend to draw up final details of the PIK program in time for Reagan's speech to farmers.

Block and congressional farm leaders have insisted that PIK must be ready by mid-month at the latest to accommodate farmers who are now making planting and financing plans for 1983 crops. Planting of some crops will begin within a month in south Texas.

Administration sources yesterday insisted that Reagan's speech Tuesday will contain no surprises, but there was speculation that the president might touch on other issues of major interest to the 6,000 delegates to the Farm Bureau convention.

The Farm Bureau and Block, for example, have lobbied the White House intensely for approval of Commodity Futures Trading Commission legislation passed by Congress last month with protection for agriculture from any future presidential trade embargoes.

The administration had opposed steadfastly "contract-sanctity" provisions, pushed by Republican farm state senators, but Reagan has not indicated whether he will sign or veto the bill. He has until the end of next week to decide.

Block and farm groups also have pushed the White House to reopen negotiations with the Soviet Union on a long-term grain sales agreement as another step in bolstering U.S. farm export income, which declined last year for the first time in a decade.

Reagan agreed last year to extend the grain agreement for 12 more months, but refused to go further without clear signs that the Polish martial-law situation had eased and that the Soviets would reduce pressures on the Warsaw government.