If the Soviet Union can be said to have a preference as to who will lead its superpower adversary through 1984, then Jimmy Carter is their man.

There are many reasons for this, but the fundamental one is that Carter supports ratification of the SALT II treaty and Ronald Reagan does not. From the Kremlin's viewpoint, that agreement, stalled by the president after the Soviet invasion of Afghanistan, stands as one still point in the gyrating world of bilateral relations.If it should collapse, it likely would take with it the complex negotiating structure built up over the last decade.

President Leonid Brezhnev made the Kremlin's view of the importance of the SALT process clear earlier last week in a speech at a banquet honoring Ethiopian leader Mengistu Haile Mariam.

"We are satisfied by the fact that Soviet-American talks on curbing the nuclear arms race in Europe have begun at last in Geneva," declared the 73-year-old Communist Party chief. "The Soviet Union will contribute to their success. Much depends on the position of the American side, the more so that the results of the talks in the last analysis are linked with ratification of the SALT II treaty, which is still blocked by the United States."

Reagan's call for an all-out arms race with the Soviet Union, scrapping the treaty and seeking new talks immediately on a SALT III treaty is the kind of program that deeply disturbs the Kremlin. There is little doubt here that the Soviets mean it when they say they will make any sacrifice necessary not to allow U.S. military superiority. But the cost to their much smaller economy, already showing stagnation in part because so much of it is reserved for military projects, would be enormous.

Thus the Soviets have reacted with bitter alarm to Reagan's platform. For example, Vitali Kobysh, a senior Central Committee foreign affairs aide who also has been covering the campaign for the influential Literary Gazette, wrote last week that early in his campaign, "Reagan left no space in his speeches for the words 'peace concern,' and did not feel uneasy about saying his arrival in the White House would mean an abrupt growth of arms and the use of the arms race as one of the U.S. political instruments, and promising that one of his first steps will be the liquidation of the SALT II treaty."

Still, neither Brezhnev nor any other leader or their top Kremlin aides has expressed publicly any comparative opinion about Carter or Reagan. The most any official has so far said was Brezhnev's reported comment to U.S. industrialist Armand Hamner several weeks ago that the Soviet leader has "warm feelings" toward the president from their 1979 Vienna summit when SALT was signed. Under the tight-lipped style of the Brezhnev leadership, this probably could be taken as an endorsement. But the Soviets do not want to damage future relations with their most powerful opponent by having inadvertently rooted for the wrong man, so comment in the tightly controlled state media has been evenhanded in this fashion: a pox on both their houses.

This attitude reflects the strain in Soviet-American relations. It is uniquely a Soviet trait to take no blame for the worsened international climate, but to heap abuse on the United States and China for forcing the Soviets to invade Afghanistan, for forging a Far East military alliance aimed at threatening the Soviet homeland, for increasing danger of the Persian Gulf war by either fomenting the hostilities or threatening to intervene with naval forces in the Indian Ocean.

Bitterly assailing both candidates as advocates of "unbridled militarism," the press has sought to enhance the Soviet position relative to Washington by pointing out that U.S. voters are unhappy with their choice Komsomolskaya Pravda, the Young Communist League's paper, said last June that 55 percent of the American electorate like neither Carter nor Reagan, and the Tass press agency two weeks ago raised that to "the overwhelming majority" of Americans.

The government paper Izvestia asserted in a recent commentary that whoever wins the election, "the US. will increase military spending, expand its military muscles and, it must be assumed, flex them every now and again in different parts of the world. The conduct of both bears witness to this."

If the Kremlin favors Carter, however, it is nevertheless not clear-cut. The Soviets are hedging their bets, for they believe, as Izvestia recently wrote, Carter "carries out in practice what Reagan promises in theory."