Moscow — Once again, a senior Soviet official has said that Moscow will not negotiate on space-based weapons this fall - unless the United States first agrees to a moratorium on the testing and deployment of such armaments.
The latest bearer of that message was Alexander Bessmertnykh, head of the US section of the Soviet Ministry of Foreign Affairs.
The public appearance of Mr. Bess-mertnykh was, in itself, somewhat unusual. He is among the phalanx of powerful Soviet officials that prefers to exercise its considerable influence behind the scenes.
His press conference here is the most recent development in a rather extraordinary campaign by the Soviet Union to convince the world that Washington - and not Moscow - is to blame for the deadlock over the negotiations.
In this country, the effort has ranged from Moscow, where Bessmertnykh became the third Foreign Ministry official to appear before reporters in recent weeks, to the Soviet Crimea, where vacationing Foreign Minister Andrei Gromyko told visiting former US Sen. George McGovern that prospects for a fall meeting between the superpowers were not encouraging - and that the US was to blame.
Further, in what appears to be an orchestrated campaign, Soviet officials in other parts of the globe have also chastized the Reagan administration for allegedly placing stumbling blocks on the road to negotiations. At the United Nations and at disarmament talks in Geneva, Soviet delegates have charged that Washington is bent on turning outer space into yet another arena for military confrontation.
The aggressiveness of the Soviet campaign - and its highly public execution - has seemed both to puzzle and irritate the Reagan administration and, most important, to catch it off guard.
Just this week, for example, US State Department spokesman Alan Romberg said the US wanted further exchanges on the negotiations to be through private diplomatic channels.
The Soviet answer, apparently, was to call yet another briefing to denounce American attitudes toward the proposed talks.
Thus, American diplomats - with tape recorders in hand - were in the audience to hear what Bessmertnykh had to say. However, they dutifully fended off questions from reporters before the briefing, listened in straight-faced silence , and afterwards made no comment as they left.
During the 45-minute discourse, they heard the intense, bespectacled Bessmertnykh charge that ''Washington in effect has no intention at all to proceed to such negotiations.''
Here in the Soviet Union, it is rare to hear such pronouncements come directly from the officials who help to shape Kremlin policy rather than merely propagandize it.
Judging from the Kremlin's latest statements, it appears that prospects for the proposed talks will rise or fall depending on whether Washington accepts the Kremlin's narrower definition of what they are supposed to accomplish.
It was Moscow that first proposed the talks June 29, suggesting that both countries should agree on a statement convening them. The proferred venue was Vienna, the time September.
Explicit in the Soviet proposal, officials here say, was ''a mutual moratorium on the testing and deployment of space armaments.''
The White House, however, says it wants the talks to include not only space-based weapons, but also ground-based nuclear arms. But the Soviets, having already walked out on two different sets of negotiations on ground-based weapons last fall, are having none of that.
And officials here charge that negotiations without a prior moratorium is tantamount to ''legitimizing'' the testing and deployment of weapons while the talks proceed.
The Reagan administration, however, argues that such a moratorium would certainly set back US research into a space-based missile defense system. The Soviets, they say, have nothing to lose from such a move because they have already built an antisatellite weapon capable of destroying the Pentagon's communications satellites.
It is on such points that moves toward negotiations have run aground.
White House and State Department spokesmen indicate that attempts are being made to work these problems out through diplomatic channels. To this, the Soviets appear to be saying ''nyet.''
Bessmertnykh was at pains to dismiss the idea of behind-the-scenes progress on the talks. The question of preventing the spread of the arms race into space, he said, ''is too important to turn it into a political game and to indulge in ploys.''