If any doubt lingered that the engine of summit publicity is self-propelling, requiring fuel of the lowest octane, the curious affair of the Weinberger letter would dispel it.

The leaking of Defense Secretary Caspar Weinberger's letter to the president Saturday plunged the summit party aboard Air Force One into a dither. Yet all it reveals -- surprise! -- is that Caspar Weinberger remains skeptical of the tattered arms control system negotiated from 1969 on by presidents Nixon, Ford and Carter.

That is news of the earth-is-round variety. Weinberger and his top civilian adviser on arms control, Richard Perle, are known to be devoted foes of arms control -- at least in any form the Soviets might buy. They view anything short of radical paring of the Soviet offensive arsenal as a risky deal, inimical to U.S. security and to the stability of deterrence.

Weinberger also, like Reagan in private moments, believes the Russians are compulsive loophole-seekers and, like little boys at the marbles ring, will fudge if not watched closely.

These are the views Weinberger and Perle brought to the Pentagon in 1981. And Weinberger has done everything short of picketing the Oval Office with placards to persuade Reagan (who needs little persuading) of their truth. Despite the pious posturing of the Russians, who have joined the game of big-time news management in Geneva, Weinberger's views are not likely to be news to Mikhail Gorbachev.

So why the dither?

Weinberger's assessment of the Soviet tendency to deviousness may be untimely but it is, alas, all too accurate. For instance, the Russians, having agreed not to "undermine" SALT II, are nonetheless encoding some of the signals from their long-range missile tests in order to thwart U.S. electronic surveillance. That's a violation certainly of the spirit and perhaps of the letter of the draft treaty.

Even so, the Weinberger view of arms control and its flaws is far from exhausting all aspects of the issue.

It takes too little account in general of the politics of arms control, which, as the recent U.S. dustup with New Zealand shows, is nudging even solid friends toward nuclear unilateralism. Such is the redundancy of nuclear power on both sides (at least in the view of bystanders) that overdoing the cheating issue is, or may seem, evasive nit-picking.

Despite the successful deployment last year of a new generation of U.S. "Euromissiles" in Western Europe, unilateralist fever is latent. The Euromissile success could be misleading. It could not have been pulled off, except that the Soviets, as usual, tried to prevail by bluster and bluff. It has been the salvation of NATO policy that the Soviets are their own worst tacticians, a state of affairs that may not continue under the wilier Gorbachev.

From the 1945 days of the Baruch Plan forward, U.S. presidents have set, and been expected to set, the pace of risk in nuclear restraint and arms control. The esoteric technicalities in which Weinberger and his aides tend to absorb themselves -- again, as a matter of duty -- yield an excessively technocratic view of what is at heart a problem in diplomacy and high politics.

Summits, as essentially political exercises, are the diplomats' meat and drink. Thus State Department advice is probably more useful to Ronald Reagan at Geneva than that of the arms technicians.

That realization may explain Weinberger's worry, and even the untimely leaking of his warning letter. It certainly makes good copy. That it should be treated as momentous revelation, however, tells less about "the news" than our overblown conception of it.