President Reagan reaffirmed his support for the Senate's version of balanced-budget legislation in a meeting yesterday with Republican congressional leaders, Senate Majority Leader Robert J. Dole (R-Kan.) said.

Despite reports of misgivings among White House officials about its impact on defense spending, Dole said of Reagan: "He likes the Senate bill . . . he wants the Senate bill."

Defense Secretary Caspar W. Weinberger zeroed in on the across-the-board reductions mandated by the balanced-budget legislation yesterday, calling it "a dangerous proposition" that would deny him flexibility in making spending cuts where they would hurt national defense the least.

"In designing and implementing the most effective defense possible within fiscal constraints," Weinberger said in a speech at Brigham Young University and released at the Defense Department, "we must make judgments about the relative priority and effectiveness of various systems."

Under the proposed legislation, he said, the Pentagon would have to cut various accounts such as procurement by a fixed amount, delaying production of some weapons that might be kept on schedule if defense managers had more flexibility.

Weinberger's latest blast against this feature of the anti-deficit legislation represents a stepped-up Pentagon campaign against the measure.

The Joint Chiefs of Staff have been studying the impact of the legislation on the Reagan military budget. If the measure resulted in negative growth of the defense budget, it would be a "travesty," Marine Corps Commandant P.X. Kelley said during a luncheon at The Washington Post last week, reflecting the growing concern of military leaders about modernization programs.

Also, at the White House meeting, Reagan raised the issue of his Nov. 19-20 Geneva summit meeting with Soviet leader Mikhail Gorbachev in arguing against a budget compromise tilted toward a House version of the legislation, Dole said.

"It could be a problem for Geneva, as the president sees it. He doesn't want to go over there having the House put the handcuffs on defense," Dole said.

A showdown on the budget legislation is expected by next week's deadline for passage of a debt-ceiling extension that would fall shortly before Reagan's scheduled departure for Geneva.

The bills set fixed annual deficit ceilings to require a balanced budget by the end of the decade, requiring the president to cut most programs, including defense, to achieve the targets if Congress fails to do so. A fiscal 1986 deficit now expected to top $190 billion would be cut to $180 billion under the Senate plan and to $161 billion under the House plan. The House plan would achieve balance in fiscal 1990; the Senate plan in fiscal 1991.

Although the House version would require bigger cuts this year than the Senate version, Senate leaders say a cut of about $10 billion is likely even under their version, with a substantial portion of the reduction coming from defense.

This triggered criticism by Weinberger and Secretary of State George P. Shultz and has given rise more recently to misgivings on the part of White House officials, including chief of staff Donald T. Regan.

The outlook for the conference, scheduled to meet Tuesday, is unclear.

A high-ranking Senate Republican aide said yesterday it will be exceedingly difficult if not impossible to get a compromise acceptable both to the White House and to the Democratic-controlled House.

In that case, Congress will face the choice of passing a debt-ceiling extension without the balanced-budget provisions, which it has been reluctant to do, or risking the possibility of an unprecedented financial default by the government if it truly runs out of borrowing power. Previously, the Treasury Department has come up with emergency financing schemes to get around debt-ceiling crises, but it has indicated it has run out of such alternatives this time.

To reach agreement by the deadline, House Ways and Means Committee Chairman Dan Rostenkowski (D-Ill.) said yesterday he will propose Tuesday that a "miniconference," composed of far fewer members than the 66-member conference committee, take over the job of reaching the compromise.

"We'll set people in a room and produce a bill by Thursday," Rostenkowski said.

Rostenkowi's suggestion parallels a proposal earlier in the week by Senate Finance Committee Chairman Bob Packwood (R-Ore.) that the issue be resolved by a small group of House and Senate leaders and a top-ranking representative of the White House.