Everyone knows Soviet-American relations are terrible, but some bubbles of possible change are rising from the depths where the big political decisions are made.

The first is the uncharacteristic statement made by Ronald Reagan this week that, "knock on wood," on his watch the Soviet Union has done none of the territorial, physical expanding of years past -- "So maybe we do have an understanding of each other." He added that his secretary of state had just held a "serious and wide-ranging" three-hour discussion with the Soviet foreign minister, and planned to see him again Monday -- "So we're not standing off and ignoring each other."

I am eager to accept Reagan's suggestion, unproven and unprovable as it is, that he has communicated where his predecessor did not that he is not to be trifled with. But it is hard to believe that he really thinks 20 months without a fresh aggression qualifies Moscow for a ribbon for good conduct or mutual understanding. Nor has anything been reported out of the Shultz-Gromyko talks in New York to indicate that progress on outstanding issues, as distinguished from a businesslike review, is going on.

The last thing we need from Reagan, however, is another lecture on the iniquities of communism and the unsuitability of the Kremlin as a negotiating partner. We need him to climb down off his crusader's horse and show evidence that he is prepared to do business if there is business to be done. What he said this week may be nothing more than mood music for the Gromyko-Shultz talks. It's the right song.

The second "bubble" of change is the debate that Moscow is holding, or advertising, about whether in its view Reagan is a hard-liner beyond redemption who must be checked and waited out, or whether there is still a chance of reviving the momentum of d,etente in his time.

Recent accounts of this debate in the American press tell of the familiar Soviet pattern of blaming the other fellow for stalemate and trolling for sympathy on the American side. But no responsible American should want to exclude the possibility that the debate may have some reality: some in the Kremlin just may feel it is foolish to let Soviet-American relations slide while, for instance, Reagan's rearmament surges ahead.

More than wishful thinking is involved here, I think. In the first negotiation that Reagan opened with the Soviets, the talks on intermediate nuclear forces in Europe, Moscow is stonewalling, waiting until 1983 to see if the allies will actually start deploying the new American missiles they have promised to deploy in the absence of an agreement.

But in the center ring, the START talks on intercontinental weapons, the Soviets have put forth a proposal that, while falling short of American terms, moves toward them in a way that has agreeably surprised some officials and earned the Soviets some respect for the internal crunching they went through to move beyond their SALT II position. One can detect within the administration a tension -- the hard line vs. the very hard line -- over how to evaluate and respond to the Soviet gambit.

For several years, the Washington policy establishment -- although not all parts of it equally -- has been in the grip of a theory holding that the Kremlin is too tied up in its succession struggle to move off a policy dime. The implication of this theory is that the United States should not extend itself to negotiate because Moscow is in no position to deal. Rather, the United States should keep on the pressure -- something this administration is already inclined to do on the basis of its reigning ideology and its view that economic vulnerability is close to bringing Moscow to its knees.

There is something to the theory of succession stickiness, but not all that much. In volatile political situations where there is a premium on flexibility and quick response (Middle East), the theory may make more sense than in slow-moving, cumulative situations requiring the careful balancing of weighty domestic interest groups (SALT/START).

In brief, it is foolish to make American policy hostage to any single, necessarily arbitrary theory of Soviet politics. Why not, instead, try to pry out the Kremlin's best START offer and see if it matches our interests?

Reagan said this week of the Arab and Israeli responses to his Mideast peace proposal that each side started by "staking out its position so as to be in a better position when it comes time to negotiate." Could it be that the Soviet Union and the United States, too, in the nuclear talks, started by staking out a position? Has it come time to negotiate?