If writing a new farm bill in 1985 was something like self-flagellation for Congress, then 1986 is taking shape as a masochist's delight.

Farm-state lawmakers have introduced a sheaf of bills, euphemistically called "technical amendments," in an effort to reverse policy decisions or to correct problems they unwittingly created in their rush to get a bill last year.

But enacting "H.R. Mea Culpa," as one House Agriculture Committee staffer called the bills, may turn out to be as difficult as was writing the farm bill itself.

The Agriculture Department, preparing to implement new farm support programs on the assumption that Congress meant what it said in the farm bill, strongly opposes the proposed changes and is warning of a presidential veto if Congress persists.

During a campaign year in which continued Republican control of the Senate is at stake, controversy over alterations to the farm bill promises to escalate into full-scale political warfare. There is political hay to be made here.

Dain Friend of Illinois, president of the National Corn Growers Association, accused members of the administration of "not following the intent of Congress and living up to their commitment to implement the 1985 farm bill . . . . the Congress must keep the administration's feet to the fire."

Republican Sens. Pete Wilson of California, James A. McClure and Steve Symms of Idaho and William S. Cohen of Maine jumped on the same critical bandwagon. Wilson said that USDA interpretation of a certain farm bill provision "defies any logical justification."

The costliest change under discussion would reverse a last-minute decision made by House and Senate Agriculture conferees in December. Under pressure from Senate Majority Leader Robert J. Dole (R-Kan.), they agreed to language that cut at least $1 billion from the farm bill and brought it closer to administration budget demands.

The language altered the way the USDA would calculate a farmer's crop yields, which in turn influence how much subsidy the grower receives. The new, more restrictive formula could result in cutting farmers' subsidies by as much as $1.4 billion over the next three years, according to some estimates.

But now, on a backdrop of protests from farmers, the House Agriculture Committee is moving a bill that would require USDA to freeze farmers' yield calculations for corn, wheat, cotton and rice subsidy payments at no less than their 1985 levels.

"The proposed change would be more fair to farmers," said an agriculture lobbyist. "They're trying to make it look like they were caught unawares, but nobody up there on the Hill can claim he didn't know what he was doing when the original language was approved."

William C. Bailey, a USDA official, told the committee last week that the administration was "especially opposed" to this change because the controversial provision "was one of the required cost-saving provisions agreed upon in order to make the bill acceptable to the administration. Such an increase in government outlays is unacceptable to the administration."

Bailey added, "We believe it is inappropriate at this time to reopen commodity provisions of the farm bill for changes . . . . [The proposals] are believed to fall outside of the scope of technical corrections."

That notwithstanding, the House and Senate are moving ahead with these other proposed changes:

*A ban on planting unsubsidized crops such as dry beans and potatoes on land taken out of production to reduce surpluses of subsidized crops such as corn, wheat, rice and cotton. Growers specializing in unsubsidized crops fear new competition from the subsidized farmers could glut their markets and ruin prices. Various House and Senate members support the ban.

*An increase in the assessment each dairy farmer pays to help finance the dairy support program to offset a 40 cents per hundredweight cut ordered by the Gramm-Rudman-Hollings budget reduction law. Rep. James M. Jeffords (R-Vt.) is chief sponsor of this change.

All three amendments are expected to breeze through the House committee this week and move on to final passage in the Senate, where support is strong.

Earlier this month both chambers completed action on "technical corrections" to the farm bill in the way a farm's acreage bases are calculated and the eligibility of individual farmers determined for subsidy programs.