Moscow — The Soviet Union is sending conflicting signals on its attitude to the proposed space weapons talks in September. The indications here in Moscow are that the ruling Politburo has still not decided whether the Soviets will attend.
The message coming from senior officials in the Soviet capital is still predominantly negative. Foreign Office spokesman Vladimir B. Lomeiko declared flatly last Friday that as far as Moscow was concerned, the United States had ''turned down'' its proposal for negotiations on a space weapons ban to get under way in Vienna.
Mr. Lomeiko stressed that the only response acceptable to the Soviets would be one that agreed that the talks concentrate solely on space arms and committed both sides to a moratorium on space weapons tests.
Senior diplomats at the Soviet Embassy in Washington have been striking an entirely different pose. In background briefings for Western newsmen they have said casually that Soviet negotiators will be at the talks - regardless of whether the US accepts the Soviet conditions.
The Soviet diplomats add ''confidentially'' that Kremlin leaders believe President Reagan will win the November election and are aiming to squeeze concessions out of him while the time is opportune.
So who is speaking for the Kremlin - the smooth-talking Soviet Embassy staff in Washington or the rough-edged Lomeiko in Moscow?
Probably both. For it has become increasingly clear in Moscow that the Soviet leadership had two entirely different motives for suggesting the space talks. And that these divided motives are possibly the result of a conflict between factions in the Politburo.
Whatever the reasons, the differing comments on the proposed talks suggest that the Kremlin has still not made up its mind what to do. And Moscow seems likely to leave a final decision to the last minute. For its final choice will be influenced by a wide range of changing factors, above all President Reagan's position in the opinion polls and its own assessment of how much can be extracted from the US leader in two months of talks before the November election.
The different motives behind the Soviets' original June 29 proposal for the talks were based on conflicting political and military interests.
On the political front, the Kremlin tacticians evidently saw a chance to trip up Mr. Reagan shortly before the election and expose him as a fraud on East-West arms issues. This was based on the assumption that Washington would turn down the call for talks, as the President had repeatedly said he had little interest in discussing space arms at this point.
Soviet officials admit privately that Moscow was caught off guard by the United States' prompt acceptance, and that the Kremlin fumbled its response for several days while members of the leadership wrestled with the problem of how to react.
The initial Soviet reply, which dismissed the American ''yes'' as unacceptable and appeared to pull back from the whole idea of talks, drew so much scorn in the West that the leadership was finally forced to issue a more carefully worded answer a week after its original proposal. It reaffirmed its commitment to the negotiations but insisted that the US must pledge not to raise the issue of nuclear weapons and must concur with the moratorium on weapons tests.
The awkwardness of the Soviet reaction was a reflection of a slow-moving bureaucratic leadership rather than a sign that Moscow had been caught out with no fall-back position.
The Soviet Union rarely, if ever, makes proposals without thinking out all the possible long-term consequences. And the second, military, motive behind the call for talks was a genuine desire to get down to negotiations on the subject as soon as possible.
The Moscow leadership is seriously worried about the US technological lead in arms development. A vice-president of the Soviet Academy of Sciences, Yevgeny Velikhov, admitted in a radio interview last May that the Soviet Union could not keep up with the creation of a ''star wars'' defense system as proposed by Mr. Reagan.
The Soviet chief of staff, Marshal Nikolai Ogarkov, has also hinted at concern among military leaders about the speed of technical arms research in the West and Moscow's failure to keep pace. Many Western military analysts attached to embassies in Moscow believe it is above all the military lobby which has been pushing for the space arms talks to begin.
Their immediate concern is to prevent the US going ahead with plans to test a new antisatellite weapon in November - hence the suggestion for talks in September plus the moratorium on all testing programs. The Soviet Union already has an antisatellite rocket but it is much more primitive than the missile the Americans are working on. It needs to go into orbit and get aligned with its target, giving the other side enough time to destroy it.
Washington has indicated it may drop its wish to push the issue of nuclear missiles at the Vienna talks. But so far it has made no comment on whether it would accept the moratorium on testing during the talks. The guess of most Western analysts is that Washington will not accept the moratorium, arguing that it has the right to develop an answer to an existing Soviet system. This would give the Soviet Union the excuse it needs to torpedo the talks, if that is what it wants to do.
Since Mr. Lomeiko is a lot closer to the Kremlin than the staff of the Soviet Embassy in Washington, that seems to be the way the wind is blowing at present. But the Soviet diplomats may yet prove to have the better foresight.
The Soviet Union has made no effort to conceal its wish to be rid of Mr. Reagan, a president it loathes more than any since Harry Truman. Judging by comments from Soviet officials and the state-run press, that political goal still takes overriding priority.
The Kremlin knows that sitting down to talks with the US will give Mr. Reagan a major political boost before the election. If it considers such a move could prove to be of crucial importance in ensuring his victory, then it will find a reason to scupper the negotiations and try to shift the blame onto the White House.
But if Soviet analysts decide at the beginning of September that Mr. Reagan is virtually guaranteed victory no matter what Moscow does, the Kremlin will change tack and do its best to exploit a brief but useful advantage.
Soviet negotiators can then be expected to turn up in Vienna regardless of American acceptance of their preconditions. They will then press for rapid progress toward a space arms ban, knowing that the US administration will be eager to demonstrate its ability to negotiate with the Russians and wary of seeing the talks break down or fail too close to election day.
''There is a fine balance of interests in the Soviet approach and it is too early to see which way they will jump,'' comments one West European arms control analyst at a Moscow embassy. ''Right now it looks as if they will not attend the talks, but that picture could change very quickly in the coming weeks.''