House Republican leaders came away from a two-hour meeting yesterday with Defense Secretary Caspar W. Weinberger warning that they support cuts in President Reagan's military buildup, possibly including curtailment of some weapons systems.

It was the second day in a row that key GOP figures in Congress have suggested that weapons may have to be cut or canceled as part of the Pentagon's contribution to a deficit reduction package. A similar suggestion was made Wednesday by Assistant Senate Majority Majority Leader Alan K. Simpson (R-Wyo.).

Weinberger, while acquiescing in some budget cuts, has zealously guarded weapon systems. The meeting with the lawmakers was closed, but Michael I. Burch, the chief Defense Department spokesman, said that Weinberger had planned to tell the Republican legislators that "any talk" of a defense budget freeze or cuts "could have an impact on the willingness of the Soviets to negotiate seriously" on arms control.

"The budget contains the smallest defense expenditure that the president can recommend while still living up to his constitutional authority as commander-in-chief," Burch said Weinberger had planned to say.

But in comments after the session, House Minority Leader Robert H. Michel (R-Ill.) indicated the Pentagon may face critical losses in Congress, such as defeat for the MX missile, unless a compromise is reached on defense spending.

Republicans will propose spending cuts "if we find that strictly adhering to a Weinberger line will cause us in the end to lose several very important votes," Michel said in answer to a question about the MX missile, which faces what could be a life-or-death vote early this spring.

"I've got enough of a reading to sense there is a view on our [the Republican] side that we can make some reductions from [Weinberger's] request," Michel added. Weinberger has agreed to what congressional leaders regard as modest cuts in the administration's planned spending for defense over the next three years.

Including the cutbacks, this would leave a military spending increase for the next fiscal year of 5.7 percent after accounting for inflation, Weinberger said yesterday. Some congressional sources have computed the increase to be larger.

Earlier this week, Michel suggested a bipartisan trade-off under which Democrats would support the MX in exchange for trimming the increase to 4 percent after inflation.

But Senate Republicans are considering more drastic steps, including a one-year, across-the-board freeze under which the Defense Department would get no more new spending authority than it has this year.

Counting the freeze on spending authority, actual defense outlays for next year are expected to rise by about $20 billion, largely because the cost of previously approved weapons is spread over several years.

This has prompted serious talk among Republicans of canceling weapons programs for the first time since Reagan began his military buildup four years ago. Simpson spoke Wednesday of breaking procurement contracts if necessary to bring down costs.

While Rep. Michel did not go that far, he reminded Weinberger that the administration is pushing for curtailment or elimination of many domestic programs and added:

"You have enumerated any number of weapons systems, none of which that I know of have been put on hold or canceled. That's the decision we've got to make on domestic programs. You've got to give the House members absolute assurance that each one of the systems are necessary for the country's defense. I'm inclined to believe there's room here for some maybe to be shaved."

Michel said he mentioned his proposed trade-off of defense cuts for the MX missile during the meeting with Weinberger but got no response. It was in this context, Michel said, that he put the secretary on notice that House Republicans would not toe the "Weinberger line" on spending if it meant risking losses on other key issues.

In brief comments to reporters after the session, Weinberger defended his proposed budget, saying it was "almost $24 billion" lower than administration estimates a year ago and noting that domestic spending has increased in the meantime.

He described the meeting as having cleared up some earlier "misunderstandings." Previously "not everybody realized the extent of the reductions that defense has already made," he said.

Meanwhile, Simpson suggested a review of congressional pay, pension and other perquisites as part of the Senate Republican drive to reduce deficits, which includes a possible one-year freeze in Social Security benefits.

"If there's a grotesque pension plan in America, it's right here in the United States Congress," Simpson said.

In comments to reporters after a consultation session with representatives of conservative groups, Senate Majority Leader Robert J. Dole (R-Kan.) indicated the Senate may consider retaining the current 16-cents a pack tax on cigarettes, which is scheduled to fall to 8 cents on Oct. 1. But he declined to say whether he favored such a move, which was suggested as a possible deficit-reducing move on Wednesday by Finance Committee Chairman Bob Packwood (R-Ore.).

Dole generally has resisted suggestions of tax increases. But others, including Packwood, have indicated tax increases are possible if the spending cut drive fails.