It is all but certain now that Soviet and American diplomatic delegations will meet in Vienna in September to discuss the possibility of preventing ''the militarization of outer space'' and related matters.
There is an interim haggle over agenda. The Soviets want to limit the negotiations to ''outer space.'' The Americans want to bring in strategic and intermediate weapons. This problem will probably be overcome, because both sides are under pressure to do precisely what is proposed - to meet and talk about restraining the arms race.
The Soviet proposal and the American response are to be seen and weighed in three contexts - in American politics, in international propaganda, and in serious talks about weapons.
The Soviets did President Reagan a political good turn by proposing the talks. It gets him off the hook of the charge, which the Democrats were intending to use against him, that he is responsible for a dangerous degeneration in East-West relations. The dialogue between Moscow and Washington is resumed. And the sequence of events will let Mr. Reagan claim, with some substance, that his policy of building weapons before negotiating has paid off.
The essential fact in the sequence is that on June 10 an American antimissile missile knocked down a target in space at a height of ''over a hundred miles'' above Earth. The Pentagon said the exact height is a ''secret.''
On the next day Soviet President Konstantin Chernenko informally proposed talks to ban antisatellite weapons. On June 14 President Reagan said he had not ''slammed the door on negotiations.'' On June 17 he made a speech to the Conference on US-Soviet Exchange in which he listed a number of talks now going on between the two countries and other subjects he said he was ready to discuss. It was by far the most conciliatory speech he ever aimed at the Soviet Union.
In effect, Mr. Chernenko sounded out Mr. Reagan on June 11. He got an informal signal of acceptance first on June 14 and then another in more detail on June 27. The formal Soviet proposal naming the time, September, and place, Vienna, was dated June 29 and made public in Moscow on that day, along with the official American reply.
Why did the Soviets make a move that would obviously help Mr. Reagan in his reelection campaign? September is the ideal time for Reagan to play the role of peacemaker. Perhaps the Soviets moved partly because they now assume Reagan will probably win reelection, hence there is nothing to be gained for them by holding back.
Perhaps the American election factor looms less in their minds than among Americans, but the successful test of the antimissile missile on June 10 looms large. It was a startling reminder to them of American technology and of how fast it is moving ahead.
That test was a warning to them, and to all, that unless something is done very soon to demilitarize outer space, the American military will move into it. It will be harder to get the military out after it is in.
The next question is whether we can expect anything to come of the talks. The answer is that nothing can come of them before election day. Formal negotiations on weapons take months, and can even take years. But there is more reason than usual to be hopeful about these particular talks.
The Soviets, clearly, want something. They want the Americans to call off ''Star Wars.'' That means that Washington has something to give which they want, just as they have something to give which Washington wants. Washington wants above all a decline in the number of superheavy Soviet ICBMs aimed at America's Minuteman missiles.
Here is the making of a possible trade - neutralization of outer space in return for a reduction in Soviet superheavy missiles.
Meanwhile the Soviets have improved their international propaganda position by proposing the conference. They had been getting a bad press in Europe for their recent surliness and intransigence.