Washington — Will they or won't they? After more than 10 days of rhetorical fencing and parrying between the United States and the Soviet Union, it's still unclear whether the superpowers will finally end the hiatus in arms negotations and meet in Vienna this fall to discuss space weaponry. But quiet diplomatic exchanges have intensified and indications are that the two sides are at least talking seriously.
''It depends more on the Russians,'' says a senior administration official, who does not wish to be identified. ''We said we would be there without preconditions. But they're sounding as if they want preconditions. So it boils down to whether they're willing to go without a lot of preconditions. I'm still hopeful we can work it out.''
State Department officials say preparations for a Vienna meeting in September are under way even though the mechanics and substance of such talks are still up in the air. The President has also issued a directive to the departments to continue working on issues raised in the aborted nuclear arms negotiations. The administration says it would raise the subject of strategic nuclear arms at Vienna but does not consider this a condition for the talks.
''We have a right to say what's on our mind, but we're not asking them to change their position,'' says the senior official. The Soviets object to any attempt to link space-weapon talks and nuclear arms negotiations.
Moscow's latest public move was a Tass statement Friday repeating the offer to hold space-weapon talks but appearing to ask for a mutual moratorium on testing of space weapons as a condition for such talks. Inasmuch as the US is preparing to conduct a test of an antisatellite weapon this fall, the administration would presumably be reluctant to accept such a moratorium.
''That would not be an attractive alternative for us because the Soviets have an (antisatellite weapon) system,'' the administration official says. ''It might be different if they were being more cooperative in other areas - in the nuclear arms talks, for instance.''
The Tass statement, however, is not regarded here as the Kremlin's reply to a message from President Reagan, which Soviet Ambassador Anatoly F. Dobrynin took back to Moscow. Washington observers are waiting for the contents of such a reply.
White House officials do not deny that, from a political standpoint, President Reagan benefits from the current bilateral diplomacy - whether or not talks actually open in September. They view the mere fact that the President is seen as willing to negotiate with the Soviets as advantageous at a time when he is intensifying his courtship of constituencies for the coming election.
Perhaps this is why the US appears willing to delay opening the talks if the Soviets want more time to prepare. ''The President is not motivated by the election,'' says the senior official. ''So if they want the talks to be two or three months from now, in November or December, that's fine by us.''
Administration officials say they have seen a lot of posturing in Moscow since June 29, when the Soviets called for talks to prevent ''the militarization of outer space.'' The alacrity with which President Reagan responded is thought to have surprised them. Although the Soviet leadership does not want to help Reagan's reelection chances, administration officials say, Moscow has consistently called for a ban on space weapons and must have calculated that the President might accept the call for talks.
Indeed, Mr. Reagan is under strong pressures from Congress and the European allies to move ahead on this issue. Even a milder Senate version of the 1984 defense-authorization bill requires space-weapon talks as a condition for testing the new antisatellite weapon against a space target. Congress takes up this issue in conference when it returns from recess.
Even if Washington and Moscow can strike an agreement to begin talks, few members of the arms control community think an actual agreement is soon achievable.
''Whether the US and the USSR are going in with good faith can only be determined when they start talking,'' says an analyst at the Arms Control Association. ''But the administration is redoubling its efforts in antisatellite weapons and it also has a $26 billion program to develop ballistic missile defenses. So the administration is committed to a militarization of outer space , and there's a dichotomy between its calls for space talks and its program. That does not bode well for ASAT negotiations.''
A major obstacle to arms agreements in the Reagan administration has been the sharp differences of view within the bureaucracy. The Defense Department has taken a hard-line approach to arms accords, while the State Department has sought a more moderate course. ''It's fairly obvious that people at Defense and the Pentagon have used the lack of talks not to do much work on arms issues,'' says one State Department official. ''So I hope the President's directive jacks them up.''