President Reagan's freshly reaffirmed ''strategy for peace'' depends on how the new Soviet leadership responds to his concept of arms buildup as a spur to arms reduction.
If only Moscow could muster the courage to do what would earn it the gratitude of all future generations: simply accept the US arms-cut proposals in the certainty that each side would retain enough nuclear overkill to deter attack by the other indefinitely. Such a bold rejoinder would require the US to forgo new missiles in Europe and permit the controversial MX to go undeveloped.
The Kremlin missed a previous opportunity to earn the world's gratitude when it rejected out of hand the ineptly presented but forward-looking arms reduction proposals of the Carter administration in 1977.
But now the Soviets are reported to have proposed similar reductions themselves in the START negotiations. They could go further, especially in an atmosphere of mutual superpower respect. Mr. Reagan sounded a welcome conciliatory note by praising their START position as a ''serious'' one.
The question is how serious the Russians will take Mr. Reagan to be. There may be some hope for mutual understanding in Soviet leader Andropov's speech almost at the same time as Mr. Reagan's. He, too, proclaimed a willingness to negotiate while keeping up his nation's military might.
Insofar as the two leaders share a strategic outlook beyond their rhetoric, they ought to be able to get together on at least the confidence-building measures proposed by Mr. Reagan. These include exchange of data on nuclear forces, improvement of the hotline for emergency communications, and advance notice of military exercises and missile launch tests. Such steps could help forestall conflict based on misunderstanding.
Mr. Reagan also asks to be taken seriously on his proposal for the $26 billion MX weapons system to be deployed in Wyoming. He argues that it is needed as an incentive for the Russians to negotiate away other arms.
Whether it would be such an incentive is one of the issues for Congress in renewing the debate on MX and now its ''dense pack'' deployment. At the moment there remain so many questions - will it work? will it require a new ABM (antiballistic missile) system? will it violate the SALT accords? - that the MX is not a credible option in the eyes of many military experts in and out of Congress. Will it be any more credible to the military experts in the Soviet Union?
Mr. Reagan seems to be floating MX as a bargaining chip. But the MX, with its image of first-strike capability, is too potentially destabilizing to be pursued unless it is determined to have an essential military use. Recall that the cruise missile was originally treated as a SALT bargaining chip to be discarded for concessions from Moscow. Now cruise missiles, with their handy ability to be carried even on fishing boats, loom as dangerous threats to military stability.
The Reagan speech contained figures and graphics to clarify the military situation for an American audience. Here again the question was how seriously the Soviet leaders would take him. They would surely note that he stressed only those measurements, such as money and missiles, in which he could show Soviet quantities higher than American.
President Reagan rightly deplored the fear of the unknown among his fellow citizens. But he failed to take the opportunity to alleviate fear by noting some of the unmatched military means that ensure his country's security even while it modernizes what needs modernizing. He omitted the perspective of showing US superiority in number of warheads, for example, or quality of submarines.
Whatever the Kremlin thinks, it should be aware of the democratic system that is now taking up Mr. Reagan's proposals - and that, no less than he, is determined to maintain peace and strength even as it winnows the ways to do so.