Leaks from the Pentagon combine with a series of official statements to demonstrate the extreme difficulty of developing a rational defense policy while living in the same world as the Russians. For the Soviet Union is maintaining a steady military buildup.

Sensible countermeasures in defense are not readily available to the United States. But because this country is taking many political steps that suggest a relaxed attitude toward security, some additional military efforts probably have to be made to warn the Russians they are playing a fool's game.

According to the defense posture statement presented to the Congress by Secretary Harold Brown last week, "Soviet defense spending has been gradually increasing . . . over the past 15 years." In particular, the Russians have strengthened conventional forces in Europe, developed a formidable navy and expanded their nuclear forces in a way that will eventually threaten this country's land-based strategic weapons.

The United States can obviously do some things to prevent the actuality - or, more likely, the impression - of a strategic imbalance in appropriations of about 2 per cent for the next five years.

He rightly gives high priority to improving the combat effectiveness of NATO forces with new tanks, new antitank weapons and a highly modern system of communications and control. The Mideast, and particularly the Persian Gulf area, is singled out as a region requiring more American attention.

But Brown and the Carter administration tend to take a dim view of some of the bigger items recommended earlier by the Ford administration. In the matter of advanced strategic weapons especially, the Carter administration has shown extraordinary self-restraint.

President Carter cancelled - without getting any Soviet concessions in return - the advanced supersonic bomber, or B-1, program. The allocation of funds for a new land-based, mobile missile, the MX, is stretched out in the current budget. Brown argues that there is already so much nuclear power available to the two superpowers that neither can acquire a decisive edge.

He pours cold water on the fashionable idea of limited nuclear war. In the posture statement he said: "Any use of nuclear weapons by the two super-powers against one another - whether tactical or strategic - would carry a high risk . . . of escalating the conflict to a full-scale thermonuclear exchange."

I find these arguments highly convincing. Indeed, I should confess to a feeling of something like reverence for Brown's defense judgments. But defense judgements need to be weighed against the political actions of the Carter administration, which - rightly or wrongly - strike many persons as indicating a lack of stomach for tough thinking on security issues.

The Panama Canal treaties are one example. The new arms-control treaty, especially when measured against the proposals originally advanced by the administration, is another. In the same mold are the withdrawal of troops from South Korea and the hostile attitude toward arms sales abroad.

Maybe all these steps are, as the president said of the Panama Canal treaties in his speech Wednesday night, "right." But the world tends to be more impressed by strategic consequences than moral motives, and strategically all these steps look like standing down. So the United States, it seems to me, needs to find defense measures that will let the Russians know this country needs to be taken seriously.

Buidling up the Navy strikes me as the obvious right step. In 1975 then-Secretary of Defense James Schlesinger expressed alarm when the fleet was at 600 ships. Now it has less than 500.

Leaks from an internal Pentago document - a first draft of the so-called Consolidated Guidance - suggest that Brown's analysts are dubious about a larger role for the Navy. They think it has the job of protecting the sea lanes, as in World War II, and of supporting American forces on shore, as in Vietnam. But they apparently do not see any special need for matching the growth of the Soviet fleet.

I cannot challenge these views. But translated into foreign policy they sound less than compelling. Everything that is known about the Carter White House, moreover, suggests poor coordination of defense and foreign policy. So I hope the Congress will press Brown to take another look at defense posture - and particularly at the naval estimates - with a view to convincing the Russians that the unrestrained military buildup is only taking them into deeper and deeper water.