Is Leonid I. Brezhnev, 72, sliding through dotage and on his way to glory? Is this lovable bear of a man, who not long ago took the diabolical Nixon joyriding through the woods of Camp David, now a doddering wreck? In a recent meeting with France's President Giscard d'Estating there were melancholy interludes when Brezhnev's mind wandered off and he became - let us notflinch from the truth - somewhat silly. Then there was that Kremlin reception at the end of which he apparently lost his bearings and almost exited through the wrong door, possibly a closet.

During May these questions lay especially heavy on the minds of all staunch disciples of the Marxist-Leninist Gospel, for early in the month came word of completion of the SALT II treaty. Now the old Bolshevik humanitarian must face the president of the United States for a summit. Is Papa Brezhnev up to it? The comrades need not worry. A Brezhnev defunct and embalmed is probably still a step ahead of his American president. Alas, Americans must face the facts: Brezhnev will be sitting across from a man who came to Washington with just six years experience in high public office. When Jimmy Carter for-sook the all-night gas stations of Plains, Ga., for his presidential inauguration, "Who's Who" still listed his occpation as a "farmer and warehouseman." Thus is Marxist historical inevitability to be aided and abetted by America's 1970s passion for amateurism.

And will Papa Brezhnev's prospering citizens be endangered by a treaty allowing Moscow unfettered use of the Backfire bomber, massive superiority in strategic payload, and vast opportunities to continue its vigorous strategic buildup? It is unlikely. Moreover, the treaty contains what amounts to a gentleman's agreement regarding verification, which must be exquisitely satisfying to the Soviets. Truth be known, living up to treaty agreements has never presented them with a problem; and if they can sell the Americans on their integrity now, well, it opens large possibilities for Soviet prospects in the future.

Still, if stipulations allowing unfettered use of the Backfire bomber, wide disparities in strategic payload, and that gentleman's agreement regarding verification are not enough to give Papa Brezhnev an easy time of it when he meets Jimmy, he can also take satisfaction that the treaty's protocol bans the Tomahawk cruise missile and the mobile basing of ICBMs - two programs essential to the Untied States if it is to remain a cloud on the Soviet horizon after 1981. Furthermore, Papa Brezhnev will be able to count on certain influential Americans' adherence to the occult to keep the U.S.S.R. strong and secure. Once the treaty is signed, these Americans will be invoking "the spirit of SALT" every time one of Washington's capitalist roaders urges even the strategic force modernization programs that the treaty now allows. Of course, the spirit of SALT is claptrap. But that will not prevent it from putting an idiot smile on the face of thousands of American policy-makers. Today there is a powerful urge among American strategic planners to believe in the plainly unbelievable. And what could be more unbelievable than that the Soviets would refrain from taking every advantage from Jimmy's amateurism?