A cloud no bigger than a man's hand is forming over Soviet-American relations. But it's Mikhail Gorbachev's hand. He has laid down the Soviet measure for the development of relations in the Bush period: "continuity" with the Reagan period. Already his officials have located a place where the new administration falls short - in defense secretary-designate John Tower's call for prompt modernization of short-range nuclear weapons in Europe. "One would hope," the Soviet Foreign Ministry said, "that these are just the hitches of the transition period. . . . "

But modernization is no passing transition hitch. It is central. The INF treaty is pulling American longer-range nukes out of Europe. NATO, seeing this coming, years ago determined to keep and to modernize the short-range missiles that constitute the first rung on the ladder of "flexible response." Without them, deterrence wobbles, Europeans grow more nervous and Americans start figuring it's better to bring the boys home.That is why NATO kept short-range missiles out of INF. That is why NATO has declined to submit issues of modernization to East-West discussion. That is why NATO strategy calls for keeping these weapons on hand until reductions in strategic, conventional and chemical forces make Europe safe enough to pull out that bottom nuclear rung.

The Kremlin knows it never had any commitment from Reagan to phase out these American weapons. The whole notion that "continuity" compels Bush to quash them is ridiculous. But the Kremlin knows too that the Germans, on whose territory all the short-range missiles would be situated and conceivably, in war, fired, have the nuclear jitters.

Gorbachev's overall diplomacy - his tank and troop cuts - has (beyond INF) a keen anti-nuclear edge. He's promised unilaterally to start reducing the Soviet Union's own tactical missile launchers in Europe. He includes (NATO excludes) the American carrier-based nuclear-capable aircraft among the conventional forces that NATO and the Warsaw Pact should negotiate down. He exploits Germany's misgivings to block modernization of the short-range nukes, in the first instance NATO's 88 Lance missile launchers.

Brent Scowcroft, the president's national security adviser, observes that Gorbachev is "making trouble" for the Western Alliance. John Tower, Bush's Pentagon choice, stayed on the same policy wavelength, but turned up the rhetorical heat when he warned an audience in Germany of Gorbachev's "charm offensive" and pronounced short-range missile modernization "essential."

The Bush administration wants to communicate its objectives, to be read correctly. Hence Scowcroft, the Kissinger hand, and Tower, the straight conservative speak out. But this new administration has yet to come to grips with key issues of tactics and strategy alike.

Tactically, some hard thinking must be done about how best to bring an uncertain Germany, with its plate already full of arguments and tensions with the United States, through an unavoidably turbulent modernization passage. It requires finding a tactful but effective way to address the Germans, cultivating the alliance and placing modernization within a larger strategic concept.

For 40 years the West's strategy has been containment. It's brought the West unprecedented peace and prosperity. Now another strategy must be devised; it will take many hands and some years. It must treat both the new possibilities and the new risks, and it must provide a reasonable context in which particular decisions - on weapons, on trade, on everything - can be set.

The strategic decision bearing on modernization, for instance, is whether the West still intends the United States to be a part of the changing European scene. If so, what is the nuclear role? This is no "transition hitch."