House and Senate negotiators reached partial agreement yesterday on a way out of the maze involving farmer income support that has thwarted their efforts to finish work on a new farm bill.

But settlement of the dispute cleared away only one of a series of problems blocking a final agreement as the conferees worked indecisively until midnight.

The impasse played a major part in the decision by congressional leaders to delay until next week their holiday adjournment, in hope of a farm bill settlement by then.

Although it failed to meet administration demands for austerity, the tentative agreement by Agriculture Committee conferees, if adopted, could lead to a three-year freeze on income subsidies paid to wheat and corn farmers.

Senate Majority Leader Robert J. Dole (R-Kan.) said the complex formula on deficiency payments, as the subsidies are called, "can be viewed as a two-year freeze or a three-year freeze."

Rep. Thomas S. Foley (D-Wash.), one of the principal negotiators on the bill's grain section, said, "Each one can tell it as they see it."

Senate conferees voted, 6 to 2, to accept the offer proposed by Foley, on condition that still-undetermined reduction requirements on corn and wheat acreage satisfy both sides.

Those reduction provisions involve the amount of land that farmers would be required to idle to qualify for federal farm-program benefits. Part of the debate centered on how much authority the secretary of agriculture should be given to order reduced plantings.

Robert L. Thompson, an assistant agriculture secretary, told conferees that the administration objects to mandated acreage reductions because it intends to eliminate them as soon as possible and send more U.S. grain into world markets.

Democrats, led by Rep. Berkley W. Bedell (Iowa) and Sen. John Melcher (Mont.), said they do not believe that the administration will retire adequate amounts of crop land to avoid massive corn and wheat surpluses.

"Many of us do not trust the secretary enough," Bedell said. "He could wreck any program we come up with . . . We'd be out of our minds if we don't mandate acreage reductions with trigger levels.

"Some of us are concerned that the secretary could wreck our program by making the acreage reduction too big. And if it is not big enough, we won't get our surpluses under control," he said.

Acreage reductions envisioned in Foley's original compromise were 20 percent for wheat and 15 percent for corn, which would have removed tens of millions of acres from production. The plan also provided for further reductions if deemed necessary by the secretary.

The compromise called for mandatory reductions whenever corn surpluses reached 1.5 billion bushels and wheat surpluses 1 billion bushels.

On income supports, the Foley offer called for holding payments at current levels for the next two years, then dropping them gradually until 1990, when they would be no more than 10 percent smaller. The costs could be more than $10 billion beyond what the administration has said it would accept.

That approach also watered down provisions for a wheat farmers' referendum on a mandatory production-control program, championed by Sen. Edward Zorinsky (D-Neb.), and a plan by Sen. David L. Boren (D-Okla.) to target income supports to medium-sized family farms.

Referendum and targeting advocates complained but to little avail. "We cannot just palm off Sen. Boren's tiering," Melcher said. "To drop it would cause problems for this bill on the Senate floor."

The conferees also battled, mostly with administration representatives, on details of a $2 billion export-subsidy program to stimulate overseas sales.

The administration objected because the open-ended program would have allowed subsidization of grain sales to the Soviet Union, one of U.S. farmers' biggest cash customers, and because the program would be mandatory.

But Bedell, Zorinsky and others argued that an existing $2 billion program, approved by the White House last spring under congressional pressure, had failed to produce results because Agriculture Department officials were not enthused about it.

Daniel G. Amstutz, an undersecretary of agriculture, told the conferees that only $46 million has been spent since May. He said another $275 million is obligated for future sales.