It is well that US administration officials quickly sought to define the scope of President Reagan's remark on Soviet nuclear ''superiority'' last week. More clarification by the White House and scrutiny by Congress are needed. They could help to ensure an accurate estimate of US strength and to convey a wise perspective on it to the public. These are important for at least three reasons:
* To assure allies and adversaries alike that American policy is based on realism.
* To give the American people confidence that they are being informed of the state of their strategic defenses without exaggeration of either assets or shortcomings.
* To support productive congressional and administration choices -- instead of arbitrary cutbacks -- in the pending reductions of massive military budget growth.
Perceptions as well as hard facts enter into these matters. The basic information on US and Soviet strategic weapons would be no news to the military of either side. It is important that public pronouncements not lend themselves to distortion causing false fears or false comfort.
Thus the necessity for perspective when Mr. Reagan introduces in a nationally televised news conference the stark note that ''on balance the Soviet Union does have a definite margin of superiority.'' When aides explained that he was probably referring to certain heavy new Soviet missiles, they in effect raised the question that bears on all efforts at drawing overall comparisons on strategic nuclear arms. So did members of both parties in Congress and from former administrations who took issue with the assertion of Soviet superiority. It is the question of the mixture of advantages and disadvantages on each side. For example, the US has more nuclear warheads than the Soviets; the Soviets have more intercontinental ballistic missiles. There are many other differences -- qualitative as well as numerical -- often dictated by the strategists' choices on each side rather than by any falling behind or leaping ahead.
So far, most arms experts have seen a rough parity in the results since Moscow overcame America's former vast superiority. Some, going back to previous Republican administrations, have questioned the meaning of ''superiority'' when levels are so high on both sides. Some suggest that ''sufficiency'' -- sufficiency to deter attack -- should be the criterion. Considering the economic drain of arms in both the US and the USSR, sufficiency at lower levels should be inviting to both Moscow and Washington.
As for the present situation, a State Department official helped to provide the needed perspective when he noted that Mr. Reagan had not said the Soviet Union could mount a first strike without fear of retaliation. This fits with the finding -- worth quoting at length -- of an exhaustive independent study by the Carnegie Panel on US Security and the Future of Arms Control last year:
''It is clear that the United States can retain great confidence in its retaliatory capabilities against the Soviet Union throughout the 1980s. U.S. leaders have every reason to believe that their Soviet counterparts see this the same way. For the foreseeable future, at least 3,000 and probably as many as 5, 000 warheads on U.S. SLBMS (submarine-launched ballistic missiles) and bombers would survive any plausible Soviet first strike. . . .
''To the degree that deterrence of nuclear or conventional attacks on this nation and its allies hinges on the risk of precipitating such retaliation, Soviet leaders should be deterred from initiating a conflict and even from taking steps which could lead to a situation in which the probability of such a conflict became significant.''