The troubling feature of the political terrain as the Geneva talks near is the way the Soviets as well as the Americans have bid up the price of the Strategic Defense Initiative, President Reagan's plan for a nonnuclear defense against nuclear missiles in space.

At this point, after all, "Star Wars" is only a research program or, if you prefer, a fantasy. The question of whether it can ever feasibly perform the more ambitious tasks set for it has to be considered highly conjectural. In Moscow as well as Washington, nonetheis that it will work -- work in the sense of transforming the strategic scene and making defense a crucial factor, one perhaps even more important than deterrence.

We have known that's what Reagan thinks: Some years ago faith conquered whatever doubt may have been in his mind. This week some of us got an up-close look at what the Kremlin thinks. A Soviet general visiting in Washington came to the newspaper for breakfast. He thundered against SDI, sounding in his judgments just as certain as Ronald Reagan that it would ultimately come to be.

Curiously, the same readiness to concede the eventual success of SDI extends to some of the most pungent American critics of the way the administration is approaching Geneva. One of them, Arnold Horelick of Rand/UCLA, suggests in Foreign Affairs magazine that the prospect of "revolutionary breakthroughs" in defense poses the greatest threat to arms control; he terms "impossible" the Reagan idea of negotiating offense down and defense up. But that prospect also offers the best hope of breaking the stalemate, if SDI is put on the table.

A strange irony is at play here. Deterrence is time-tested, road-tested, warrantied, the works -- but still leaves many people scared and skeptical. Defense is new, remote, untested, far unlikelier -- but has quickly won an elite corps of believers, East and West.

Is it that people crave certainty, even an illusory or fearful certainty, to satisfy a sense that they must know what their fate is, regardless of its terrors? Is it that SDI confirms for us our sense of being a special place not subject to the familiar mortal perils and limits on human endeavor, and confirms for the Russians their sense of our intrinsic menace and superiority? Could the Russians know something about SDI's feasibility, or about their and our relative technological competence, that some of us Americans don't know?

No matter. The administration appears intent on preserving an opening for SDI. It is going to Geneva prepared to forgo any possibility to limit the strategic and intermediate-range nuclear weapons that have heretofore been the mutual Soviet-American concern, if the cost is yielding SDI.

The administration, of course,

does not see it exactly that way. It

counts on the Soviets' eventually

coming to a "rational" conclusion

that their national interest requires them to follow our example

and to get out of nuclear offense

and into nonnuclear defense. That

the Soviets insist they will beef up

their offense instead, and that

they are expected to spend the

next year or two battering SDI in

European and American opinion,

is taken by the administration as a

tactical program that Americans

must calmly wait out.

Does the administration, in declaring SDI not negotiable and in

mortgaging all of arms control and

much of the whole course of Soviet-American relations to SDI,

know what it is doing? For that

matter, does Moscow, in giving

voice to a tremendous alarm

about SDI, know what it is doing?

To a certain swath of Americans, nothing confers value on an arguable project so much as the spectacle of the Kremlin's hostile and perhaps disingenuous objection to it. The Soviet Union is fresh from a tremendous and costly misreading of Western opinion -- its failed effort to balk deployment of new American intermediate-range missiles in Europe, while its own deployments continued. Has it, in its campaign against SDI, launched into yet another frantic misreading of even greater potential cost?

In a democracy, where presidents are accountable to the people, defense against nuclear attack turns out -- once it goes critical in public opinion -- to be an extremely powerful idea -- morally and perhaps also politically irresistible. Our dilemma arises from the pressures on Reagan to move the idea toward reality, without knowing whether it has reality or whether the process of finding out may overwhelm the fragile U.S.-Soviet enterprise.