SECRETARY VANCE says he's disappointed that the Russians accepted neither of the two strategic arms proposals he brought to Moscow - the Vladivostok missile levels minus cruise missiles and Backfire bombers, or substantial reductions - and so are we. But we are not desolate to the point of thinking that the United States should either sweeten its offer to make it more appealing to the Russians, or batten down the hatches for the resumption of the cold war.

The negotiating position presented by Mr. Vance gave Moscow the chance to limit the new cruise-missile technology in which the United States is far advanced, in return for the missile reductions in which Americans have a special interest. That offer is no less sound for the Kremlin's inability to accept it quickly. On the contrary, the position is complex and far-reaching and demanded of the Russians a measure of political flexibility that few, if any, knowledgeable Americans expected them to demonstrate on the spot. That they are interested in a better regulated relationship with Washington is evident from their agreement to set up 10 working parties on as many separate issues (arms sales, Indian Ocean, etc.). But the SALT issue obviously posed tougher problems. Their failure even to offer counter-proposals, other than to repeat their old offer to ratify a version of the Vladivostock agreement, which no longer commands a consensus in Washington, shows just how immobilized they are.

Why did Moscow react as it did? Doubtless we'll all learn more in the days to come. It is conceivable, for instance, that the Russians gagged on the human rights policy, which President Carter has made a part of his overall approach to the Kremlin. It is possible the Russians may be so bent on achieving strategic superiority that they could not hage failed to reject any American proposals aimed, as Mr. Carter's were, at stabilizing at lower cost and risk a strategic balance.

Tentatively we would guess, however, that the Kremlin is coming into the grip of a succession crisis that has rendered it unable to take any but the smallest consensus decisions. That much is suggested by reports on the failing health of Leonis Brezhnev. There is much that outsiders don't know about Kremlin politics. One thing they do know is that without strong leadership the Kremlin hunkers down. If Mr. Brezhnev is ailing physically, then unquestionably he is also ailing politically, and his leadership colleagues are focused not on policy but on politics. If that is so, then that is all the more reason for Washington to hunker down as well.

To judge by Mr. Carter's remarks yesterday, he is prepareed to do just that. He made it clear to Moscow that the United States prefers to serve its own legitimate security interests by pursuing mutually advantageous measures of arms control, and that he will consider taking independent steps to build major new weapons system only if the Kremlin leadership, old or new, shows as time goes on that it rejects the American commitment to serious arms control.