For more than two weeks now, one of the principal concerns among Soviet and foreign diplomatic observers here focused not so much on a threat of war as on chances for making a better peace.

Hopes and speculation that the two superpowers may find a way to break out of their present impasse were raised by the meeting between President Reagan and Soviet Foreign Minister Andrei Gromyko Sept. 28.

On Tuesday, President Konstantin Chernenko voiced his view on the subject in an unexpected and dramatic fashion by granting an interview to an American correspondent and delivering an intriguing and conciliatory message.

Chernenko's interview with The Washington Post was given added significance because it was the most authoritative Kremlin pronouncement on the subject of Soviet-American relations since the Reagan-Gromyko meeting.

Well-informed observers here said the tone and content of Chernenko's interview seemed to reflect the Soviet leadership's "basic positive assessment" of the Washington talks as well as guarded hopes that a shift in relations is possible.

The interview was also significant for what the Soviet leader did not say. By avoiding such divisive issues as the deployment in Western Europe of U.S.-made Pershing II and cruise missiles, Chernenko may have been seeking a conciliatory posture.

The Soviet leader, however, did not hide his disappointment over the absence of "practical steps" to match Reagan's conciliatory rhetoric. Nor did Chernenko obscure his distrust of Reagan.

Even so, Chernenko professed optimism that the two superpowers will move toward stability, if for no other reason than a respect for each other's nuclear might.

One of the most intriguing aspects of his interview was its timing. Coming before Sunday's foreign policy debate between Reagan and Walter F. Mondale, Chernenko's pronouncements and specific offers on arms control talks appear to have been designed to inject Moscow's views into the presidential contest.

Western observers here saw the move as placing additional pressures on Reagan to commit himself to some steps that would produce a modest accord to limit the pace of the arms race.

But Chernenko refused to be drawn into a discussion of the U.S. elections and he made it clear that he was prepared to deal with "any" American president.

The true nature of Moscow's motives in addressing the American people now is simply not known. Chernenko may have wanted not only to start a diplomatic initiative but also to stop rumors about his health.

His statements were notable for several reasons: Chernenko's words appeared designed to shift the tone of Soviet diplomacy from invective to measured conciliation. He expressed guarded optimism about the possibility for improved relations "irrespective" of who will be in the White House. He emphasized that the Soviet leadership was united. During the conversation, he made a point of saying that he was replying on behalf of the Soviet leadership. Although the points he selected for a possible compromise had been advanced earlier, Chernenko presented them as a package, indicating that resolution of any of them would lead to a meaningful dialogue.

Two key questions remain unanswered. To what extent were the Soviets encouraged by the Reagan-Gromyko meeting? Was Chernenko's interview designed to prod the President toward a rapprochement or was it merely a tactical ploy to exploit his difficulties before the debate and the election?

The Soviets are known to be hard bargainers unlikely to damage their long-term interests by trying to make short-term tactical gains. Tending to confirm this is Chernenko's stated readiness to deal with any U.S. president, including Reagan.

One has the impression here that the Soviet leadership continues to believe that Soviet and American interest should be leading the two superpowers into a more civilized relationship.