The Reagan administration opposes congressional calls for a U.S.-Soviet freeze on nuclear weapons, saying it would put the United States "into a position of military disadvantage and dangerous vulnerability."

Responding to bipartisan resolutions introduced Wednesday by 19 senators and 122 House members, Richard R. Burt, the State Department's director of politico-military affairs, opened yesterday's press briefing with a formal reply.

"While we understand the spirit that motivates the freeze effort, the administration cannot support the freeze itself," Burt said. "A number of compelling facts argue against a freeze."

Burt's words were intended to counter both the congressional resolutions--sponsored in the Senate by such figures as Edward M. Kennedy (D-Mass.) and Mark O. Hatfield (R-Ore.) and in the House by Jonathan B. Bingham (D-N.Y.), Edward J. Markey (D-Mass.) and Silvio O. Conte (R-Mass.)--and a nationwide disarmament movement.

The resolutions, intended to express the desire of Congress if adopted, call on the United States and the Soviet Union to seek a mutual and verifiable freeze on testing, production and further deployment of nuclear warheads and then negotiate major reductions on both sides.

In an initial reaction Wednesday, Secretary of State Alexander M. Haig Jr. called the idea "not only bad defense and security policy" but "bad arms control policy as well." In delivering the administration's formal and more considered response, Burt sought to be more conciliatory.

"The people who support the freeze share our desire to reduce the threat of nuclear war and to reduce existing nuclear stockpiles," he said. "Our disagreement is not one of strategy or objectives; it's really one of tactics. What's the most effective way to stop or curb the nuclear weapons competition?"

The Soviet Union, he asserted, has an overwhelming advantage over the West in Europe in intermediate-range missiles. Therefore, he contended, instituting a freeze of the kind proposed in Congress would block plans to deploy offsetting new-generation U.S. Pershing missiles in West European countries, halt President Reagan's program of modernizing the strategic-weapons arsenal and eliminate any incentives for the Soviets to bargain on the basis of the plan put forward by Reagan Nov. 18.

That plan calls for eliminating the Soviet SS20 missiles being deployed in Eastern Europe in exchange for canceling the North Atlantic Treaty Organization's scheduled placement of the Pershings in West European land bases, where they would be capable of striking the Soviet Union.

He said the freeze proposal is essentially the same idea that has been put forward by Soviet President Leonid I. Brezhnev. He added that it was only because of NATO unity in moving ahead with the Pershing deployment and the U.S. modernization program that the Soviets, after long heel-dragging, agreed to the intermediate-range missile reduction talks under way in Geneva.