Defense Secretary Caspar W. Weinberger offered at a White House budget meeting yesterday to agree to a one-year "freeze" on military pay in 1986 as the Pentagon's contribution toward reducing the deficit but balked at other deep cuts in the defense buildup, administration sources said.

Weinberger, at a luncheon with President Reagan and his group of budget advisers, outlined a plan for defense savings that would allow the military to receive a scheduled 4 percent pay increase in January, then hold pay at existing levels for 1986, the sources said.

Weinberger's suggestion would affect 2.1 million Americans in uniform. Congress has rejected proposals for a military pay freeze in the past.

"We tried it once and it was dead the moment it got up there," a White House official said.

Administration sources said Weinberger continued to resist a proposal by Office of Management and Budget Director David A. Stockman to scale back the defense buildup over several years by restraining weapons procurement as well as personnel costs.

Reagan tentatively has approved a proposed 5 percent pay cut in 1986 for civilian government workers, who will get a 3.5 percent pay raise in January.

The 5 percent cut would cover civilians working at the Pentagon.

Administration sources said Weinberger's offer to freeze military pay for one year would save more than $4 billion in fiscal 1986, which begins next Oct. 1.

The White House goal for Pentagon savings is $8 billion. Officials said Weinberger's overall proposal fell short of that, but it was not known by how much.

"He's not too terribly far away," one official said.

Weinberger also counted savings from the planned civilian pay cut, about $1 billion next year, in his proposal, officials said. However, this saving already was included in the $34 billion in domestic budget cuts Reagan has approved.

Officials said Weinberger also "reestimated" the actual spending planned next year for the Pentagon. The White House had been using $286 billion. Weinberger was using a higher figure but agreed to come down to the White House estimate. Officials said this means Weinberger would have to find less savings than if he used his previous estimates.

Sources said the meeting yesterday, over baked chicken in the White House Cabinet Room, was contentious. Several Cabinet members pressed Weinberger to come up with a bigger "contribution" toward reducing deficits than he has so far, they said.

The White House has set a goal of reducing the budget deficit from more than $200 billion next fiscal year to less than $100 billion by 1988.

White House spokesman Larry Speakes said that no decisions were made in the meeting yesterday and that more sessions would be held soon.

Rep. William L. Dickinson (R-Ala.), ranking minority member of the House Armed Services Committee, met separately with Reagan and urged him to be "realistic" in his defense spending request, the sources said.

Treasury Secretary Donald T. Regan told a breakfast meeting of reporters yesterday that the military must accept its share of budget savings next year. If not, he said, "I don't think our cuts" in domestic spending "have a prayer in Congress."

Regan said that the president had achieved a bigger military buildup, after inflation, than he promised in his 1980 election campaign, and that big prospective deficits were a threat to the economy.

"From an economic point of view, the economy of the country, in my judgment, is almost as important as our defense against outside enemies, and with these huge deficits we could be in danger of losing our economy," the Treasury secretary said.

A "pause for a year" in the Pentagon buildup "is not asking too much," he added.