The Carter administration has reached a compromise with the Soviet Union on major points of a new pact to limit nuclear weapons that will come under critical scrutiny in a Senate hearing this week, while negotiations proceed in Geneva.

"We have started to thrash out with the Soviets the framework of a new agreement," chief U.S. arms negotiator Paul C. Warnke said in Geneva yesterday.

Some details of the new pact were reported in yesterday's edition of The New York Times and other elements and interpretations were provided yesterday by sources in the administration and Congress.

The basic trade-off in the potential accord, officials say, will allow the United States to deploy without penalty 120 bombers armed with the newest American weapon, air-launched cruise missles. The Soviet Union, in turn, will escape the 50 per cent reduction which the United State sought in the deployment of the largest Soviet land-based intercontinental missile, known as the SS-18.

Numerous complex compromises are contained in the proposed accord, which is still months away from completion and remains officially secret. It would replace the 1972 U.S.-Soviet limitations on intercontinental missiles and bombers which technically expired on Oct. 3.

Nevertheless, sharp controversy already has broken out over "leaked" versions of the new terms, with supporters hailing them as "a damned good deal" and "a fair balance," while critics are assailing the terms as "inadequate," "unbalanced," and "a great disappointment.

Secretary of State Cyrus R. Vance on Friday will make the first trial run for the accord as it was worked out in recent negotiations here with Soviet Foreign Minister Andrei A. Gromyko, with President Carter making the major U.S. decisions. Vance will appear in closed session before the Senate Armed Services Arms Control Subcommittee headed by Sen. Henry M. Jackson (D-Wash.), with Senate leaders also present.

What has emerged from U.S.-Soviet bargaining, officials concede, is not the "radical departure" in arms control that the Carter administration set out last March in Moscow, and which the Soviet Union scorned.

Instead of the "drastic reductions" that Carter sought in the weapons ceilings set by President Ford and Soviet leader Leonid I. Brezhnev at Vladivostok in 1974, only a modest cutback in those limitations is now projected.

The outcome, officials contend, should not be measured against what was envisioned, but against advances over the 1974 terms.

At Aladivostok, the two nations set a ceiling of 2,400 on each side's strategic missiles and bombers, with a sub-ceiling of 1,320 on all weapons with multiple warheads. They have now agreed to cut the overall ceiling up to 10 per cent, or to a range of 2,160 to 2,250 delivery systems. This type of cutback has been in earlier proposals for talks (SALT) accord.

The more significant variation is the intricate compromise worked out on counting bombers equipped with multiple cruise missiles, which are similar to low-flying pilotless aircraft. Initially, the United States insisted that cruise missiles were totally unlimited by the Vladivostok agreement; the Soviet Union insisted that each bomber armed with cruise missiles should count against the 1,320 limit for all delivery systems with multiple warheads.

Under the compromise, the 1,320 ceiling would be retain for all types of weapons with multiple warheads. But there would be another sublimit of 1,200 on intercontinental missiles with multiple warheads, excluding bombers.

This means, officials said, that between the 1,200 and 1,320 ceiling the United States would be abloe to deploy 120 air-launced cruise missiles without counting them against the 1,320 limitation on combined land launched and sea-launched missiles, and bombers with air-launched missiles.

That numerical device would accommodate American interests, although the U.S. Air Force originally wanted to deploy about 240 B52 bombers with cruise missiles, to offset the loss of the B-1 bomber program canceled by the President.

Another numerical device partially accommodates competing Soviet and American interests in the totals of launchers with multiple warheads.

The major U.S. concession to the Russians drops the President's insistence on cutting in half the numbers of the largest Soviet missiles, the SS-18s. They would have been reduced from 308 to 150 under the original Carter plan. In the new deal, the Soviet figure would remain at 308.

As a measure of compensation to the United States, agreement was reached for a sub-limit of 800 to 850 in the total number of Soviet landbased missiles with multiple warheads.

Administration officials claim that this will significantly curb the numbers of Soviet missiles that can threaten the American land-based missile force, at least partially making up for the lack of reductions in SS-18 numbers.

The Defense Department, some civilian officials claim, expressed a preference for limiting all Soviet land-based missile with multiple warheads, in part to curb the Soviet SS-19, regarded as a greater danger to the U.S. missile force.