With American warships maneuvering off the coasts of two Soviet client states, Nicaragua and Libya, the Reagan administration is demonstrating that its Soviet policy is an eclectic hybrid fitting no clear pattern of the past.

Two months ago Secretary of State George P. Shultz described that policy to the Senate Foreign Relations Committee, saying that the administration had embarked on a course going beyond either "containment" or "detente." Some saw new American militancy in his remarks; senior officials said instead that the new emphasis would be on "active and productive dialogue."

In fact, U.S. policy has gone in both directions. The United States is projecting its military power with exceptional assertiveness against Soviet-supported nations. At the same time, the administration is boasting of having achieved "encouraging progress" on several fronts in negotiations with the Soviets, though these gains have been largely on marginal or technical issues.

To critics this is a crazy-quilt pattern of strategic incoherence. But administration policy makers see it as an effective combination of firmness and flexibility. The double-track approach, senior officials say, enables the administration to project American strength, to hold a diplomatic door open to the Kremlin and, by no means least of all, to deflect charges that the administration is resisting compromise with the Soviet Union.

The Soviet Union, in private even more than in public, scoffs at American claims of diplomatic advances as highly exaggerated, inflated for domestic political purposes. Nevertheless, the Soviet leadership of Yuri V. Andropov, preoccupied with the badly sagging Soviet economy, has for its own self-interest been responsive to U.S. diplomatic probing, even while minimizing the results.

What has been obscured in the process is that the United States, not the Soviet Union, has made the largest shift of position. The Reagan administration began by saying that it would link all subjects on the American-Soviet front, from Afghanistan to Poland to arms control.

When the Reagan administration backed off that all-or-nothing approach, the Soviet Union shifted from its contention that negotiations with the administration were hopeless. But what impelled the Kremlin's switch, senior U.S. officials say, was not any softening of the U.S. line, but the sustained buildup of American military strength and a realization in Moscow that Reagan might well run for a second term and win.

"If Reagan announced tomorrow that he wasn't going to run," one senior U.S. diplomat said recently, "we could all relax on preparing briefing papers on Soviet issues."

Soviet sources concede in private that the prospect of a second Reagan term has affected Soviet diplomatic planning. But they stress that none of the central issues dividing the two superpowers is near a solution.

That is the single point on which the two sides agree. Before the United States launched its current naval maneuvers, one senior U.S. official likened the recent gains made in American-Soviet diplomacy to "a delicate flower." At this stage, he said, "it wouldn't take much to knock all of this into a cocked hat because it has no roots, it has no depth yet."

The Reagan administration is gambling that its displays of force in Central America and in the Mediterranean will not disrupt these aspects of U.S.-Soviet relations.

Brief encounters in these regions have been treated on both sides as passing incidents. Extended military maneuvers in zones where American-Soviet interests are in conflict, however, do raise the prospect of incidents that could entangle the two superpowers.

In operations off Libya's coast, where American naval units are maneuvering, or in Chad, where American-supported forces are fighting Libyan-supported rebels, U.S. officials regard the risk of a clash with Soviet interests as quite low.

The Soviet Union, U.S. officials said, is always wary of tying itself to the ventures of Libya's Col. Muammar Qaddafi, except after the danger of involvement has passed.

The all-but-open challenge to Soviet interests by U.S. warships astride Soviet supply lines to Nicaragua, however, is more than a minor stain on Soviet prestige.

In explaining its actions, the United States has gone considerably beyond its first rationale of simple "training maneuvers" to declare, in the words of Shultz, that a corollary purpose is "to underline the deterrent capability of the United States . . . to everybody, our friends and our adversaries alike."

Even dressed up in diplomatic circumlocutions, that is a bold explanation for a checkmating move on the superpower board, especially when it is coupled with the implicit threat of imposing a sea blockade around Nicaragua. The Soviet reaction so far has been relatively passive, limited to denunciations of the American naval operations as "sea piracy" and "manifest blackmail."

Administration officials calculate that Moscow will not go beyond verbal attack on the American operations, and they cite numerous inhibitions on the Kremlin to sustain that judgment.

The Soviet Union has avoided any pledge that would commit it to Nicaragua's defense in event of a shooting encounter with other nations. When a senior Soviet official reiterated Moscow's pledge of support for Nicaragua in Managua last week, he specified "political," not military, support. Furthermore, the Soviet Union is at a great disadvantage, geographically and militarily, for mounting any challenge there to American power.

Even so, the Reagan administration's increasing military assertiveness is bound to be taunting to the Andropov leadership.

The United States is now openly or covertly supporting anti-communist forces in Nicaragua, El Salvador, Afghanistan, Cambodia and elsewhere. There is no way Moscow can accept this as tolerable symmetry, equatable with Soviet support for pro-communist warfare in those areas. For the Soviet Union, "liberation warfare" runs only in one direction.

Will the Kremlin leaders nevertheless conclude, as the Reagan administration is doing, that all the limitations operating on them foreclose countermoves? Seemingly absorbed in its own turnover in power, the Soviet Union displays no signs of interest in such ventures, although the Reagan administration prefers to attribute that to its own toughness, not to Soviet forbearance.

From the administration's perspective, it has demonstrated the ability to pursue "a policy of strength" toward the Soviet Union--more than match it in fierce rhetoric, such as Reagan's "evil empire" speech, and still conduct serious diplomatic business with the Kremlin.

Shultz, meeting with Senate and House leaders just before the congressional recess, described his recent extended discussions with Soviet Ambassador Anatoliy F. Dobrynin and other American-Soviet talks, as evidence that relations between the two nations are now on a productive course.

Reagan similarly told a press group, "we're trying to indicate that we don't have to be nose-to-nose" with the Kremlin. He cited the recent long-term grain agreement with the Soviet Union as the latest example of effective negotiations.

These have ranged from the Soviet agreement to permit the emigration of Pentacostalists sheltered in the U.S. Embassy in Moscow through the removal of some technical barriers in arms-control negotiations to ending the long stalemate in the Madrid conference on European security and cooperation.

These gains do not touch the key issues, however. Shultz told one interviewer, "The thing that has plagued U.S.-Soviet relations over the years--namely, the Soviet behavior in particular geographic areas like Afghanistan or Poland or Kampuchea Cambodia or Central America, southern Africa or wherever--there seems to be no change in the rather aggressive pattern, very aggressive pattern, that they have employed."

The Soviet Union, in turn, has its own fixation: to forestall the deployment of American Pershing II missiles and cruise missiles in western Europe that is scheduled to begin in December. Negotiations on this issue are in recess in Geneva, along with parallel talks on limiting intercontinental missiles.

With the uncertainties ahead in Central America, this gap in the negotiating sequence makes the usual diplomatic hiatus of August a time for speculation about the state of U.S.-Soviet relations when Shultz and Soviet Foreign Minister Andrei A. Gromyko are next scheduled to meet: twice in close succession, in Madrid in early September to sign the accord on European security and cooperation and later in the month at the United Nations.

If official American projections are borne out, the United States and the Soviet Union will then be facing the old, formidable obstacles rather than a new magnitude of tension. But that assumes they can ride out any polarizing incidents in regions where neither of them has control of all events.