House and Senate conferees, seeking a compromise multibillion-dollar farm and food stamp bill acceptable to President Carter, agreed yesterday to increase ceilings on support payments to farmers.

Splitting the difference between Senate and House plans, the negotiators set a limit on support payments to grain and cotton growers at $40,000 for 1978, $45,000 for 1979 and $50,000 for 1980 and 1981

The limit is $20,000 per farmer.

Under the compromise, payments for disaster relief would not be counted against the ceiling. A separate ceiling of $52,500 in 1978 and $50,000 in 1979 would apply rie growers, but after that a single $50,000 limit would apply to all crops.

The conferees moved to comply with administration economy proposals by adopting a House plan for raising wool supports rather than a more costly Senarte plan.

They also adopted a Senate-sponsored amendment to extend an 80-per-cent-of-parity floor under milk prices for two years rather than four years, as proposed by the House.

The panel agreed to let most major portions of the bill extend for four years beginning in 1978 rather than five years, as proposed by the Senate.

The conferees will try to complete work on the bill before Congress begins its month-long recess Friday, but final passage is not expected until September.

At issue is a $10.5 billion to $1.15 billion House bill passed last week and a Senate version that calls for higher spending levels.

House Agriculture Committee Chairman Thomas S. Foley (D-Wash.) said that even if final House and Senate votes are delayed until September, completion of the conference agreement this week would allow the Agriculture Department to give wheat farmers tentative outlines on an acre-age-reduction program on 1978 crops.

Three straight years of 2 billion bushel-plus wheat crops have dropped wheat prices below production costs, and Agriculture Secretary Bob Bergland said he may activate the acreage-cutting plan under authority that would not be available for the 1978 corp until the pending farm bill passes.

Officials want to announce their plans - even if they are tentative - this month because growers will begin planting 1978 winter wheat late next month.

Foley said key issues facing the Senate and House farm leaders include proposed levels of supports for major crops beginning in 1978 and a House approved plan, strongly opposed by the administration, to boost the market price of sugar.

Foley said congressional leaders may offer a compromise on the sugar support issue.

The House set the corn support target at $2.10 a bushel in 1978 with increases in future years. The Senate bill, in contrast, would start supports at $2.28 a brushel in 1978, and the difference could cost an additional $1 billion a year.

Others issues to be resolved in conference committee involve extension of the $5.6 billion food stamp program.