Soviet President Leonid Brezhnev, moving to increase pressure on Ronald Reagan from US anti-nuclear advocates, has called for early strategic-arms talks and a partial ''freeze'' on strategic weapons.
The freeze suggestion came with a significant loophole -- allowing at least limited ''modernization'' of existing forces -- but bore enough resemblance to various proposals raised inside the United States to worry some Western diplomats here. They argued that the proposal would perpetuate a Soviet edge in strategic delivery vehicles and ease pressure on the Kremlin during eventual negotiations.
In additional, since US officials have already rejected any freeze prior to implementation of rearmament plans, the diplomats said Moscow would win political points from the expected American rejection of the Brezhnev proposal.
The Soviet President rejected the strategic-arms-control blueprint offered May 9 by Mr. Reagan as ''absolutely one-sided'' but stopped short of saying the Kremlin would delay resuming talks until the Americans came up with something more acceptable.
The Brezhnev remarks, in a keynote address May 18 to a congress of the Communist Party's youth wing, followed a statement from a senior Soviet official to the Monitor that Moscow would negotiate ''even on the platform Reagan has suggested.''
The official said Soviet counterproposals were being prepared. He did not say whether Moscow would be ready to resume strategic-arms talks next month, as Mr. Reagan had suggested. Nor did Mr. Brezhnev in his May 18 speech.
President Brezhnev's remarks were taken by diplomats here as part of intensified superpower sparring in the run-up to resumption of negotiations.
His aim seemed to be to retake the public initiative on arms control in the wake of President Reagan's May 9 proposals and to encourage domestic uneasiness with Mr. Reagan's arms policy.
President Reagan proposed a phased strategic-arms reduction, beginning with a one-third cut in warheads and providing that no more than half of the remaining total be based on land. His clear aim is to get at Moscow's force of land-based ''heavy'' missiles, which US officials fear could destroy the American force in a first strike. The Soviets' strategic force consists mostly of land-based missiles, while the Americans' is biased toward submarine launchers.
Mr. Brezhnev did not address the specifics of the Reagan proposal, such as its emphasis on warheads rather than strategic delivery vehicles. Nor did the Soviet President present a detailed platform of his own for strategic talks.
Instead, he coupled a general rejection of the Reagan package as part of a bid for US ''superiority'' with Soviet guidelines avowedly aimed at ensuring ''that the talks should begin immediately in the right key.''
Mr. Brezhnev said: ''The American position is absolutely one-sided . . . because the United States would like, in general, to exclude from the talks the strategic arms it is now most intensively developing.'' This was seen as a reference principally to the ground-hugging cruise missile and to potential deployment of the new B-1 bomber and MX missile.
The Soviet President suggested three principles for resumed talks: that they not become ''a cover'' for US rearmament, that the Americans hold to the ''equality and equal security'' that Moscow says exist at present, and that ''everything positive'' achieved in earlier talks be preserved. The last point was a clear reference to the 1979 SALT II accord, which the US Congress has not ratified. The Soviets advocate ratification but do not insist on it as a prerequisite for new talks.
Mr. Brezhnev said Moscow wanted to begin talks ''without delay and without any strings attached.''
He then raised the proposal of a ''freeze'' that ''would facilitate . . . headway'' in negotiations and start concurrently with them.
Unlike the freeze proposal of US Sens. Edward M. Kennedy and Mark Hatfield, Mr. Brezhnev's suggestion did not explicitly cover both production and deployment. That is, it said ''strategic armaments'' would be ''frozen quantitatively,'' but did not specify the basis for computing current levels.
On qualitative strategic arms capabilities, the proposal stopped short of suggesting a total freeze, although it implied this could be agreed on eventually.