The new improved Vienna detente that Jimmy Carter and Leonid Brezhnev will seek this weekend may work wonders for the nuclear arms race and economic bridge-building. But it has little chance to lighten or brighten U.S.-Soviet conflict in Africa and the Middle East.

Indirectly and more soberly, Secretary of State Cyprus R. Vance addressed this general point yesterday, describing the summit at a press conference as a chance for the two nations "to move away from the peaks and valleys, the ups and downs we have seen to a more stable relationship."

The already negotiated strategic arms limitation treaty (SALT II) THAT CARTER AND BREZHNEV WILL SIGN IN VIENNA HAS CLEARLY BECOME THE "PEAK" OF THE U.S.-Soviet relationship. And the regional conflicts of Africa and the Middle East remain the dangerous "valleys" that directly pit U.S. and Soviet interests.

Carter can expect to get an earful on the Middle East - a Russian valley of humiliation at the moment - but he will face a lot a stonewalling by Brezhnev on the racial conflicts of southern Africa, where the Russians apparently see the forces of history building them an unassailable peak that does not need to be discussed.

And if recent Russian visitors to the Washington area are a guide, Brezhnev is likely to counsel Carter that more "downs" in the Third World are inevitable for both sides, which should try to accept regional defeats as historical developments rather than expecting the SALT success to moderate their outcomes.

Some senior administration officials hope that Soviet appreciation of the difficult test the SALT treaty faces in the Senate will lead Moscow to be especially cooperative in Africa and the Middle East over the next six months. While small tradeoffs can be expected, and enduring "linkage" of this kind is unlikely to emerge from Vienna.

"More Angolas for you, more Sadats for us are over the horizon. We have to live with it," a Russian visitor said recently, rejecting the notion that SALT would lead to a rigid code of conduct in situations like the West's defeat in Angola in 1976 and Egypt's defection from the Soviet Camp in 1972.

Specific Middle East topics that are likely to come up include American hopes that the Russians will not block United Nations peace-keeping troops from policing the Egyptian-Israeli peace treaty when the Security Council votes on that issue next month.

This could be balanced by Russian concern over the Idian Ocean, and the two topics may intertwine. Proposals for increasing the U.S. military presence in the Middle East through increased naval deployments into the Indian Ocean are under study in the administration, a move that the Russians would view as probably killing any chance for a renewal of the suspended Indian Ocean arms control talks.

In southern Africa, there are no obvious balancing factors. Carter's top priority is likely to be trying to get Russian cooperation in reducing the bloodshed in Zimbabwe-Rhodesia, a step some of his top advisers think can be achieved by a cut in Soviet arms deliveries to the Patriotic Front guerrilla forces. But the Russians seem to see the breakaway British colony as a place where the West only has assets to lose, not to trade.

The Russians have analyzed U.S. policy in southern Africa as indecisive and conflict-ridden, a sharp contrast to the deviousness and strength they impute to American policy in the Middle East.

Much of any Middle East conversation will be devoted to bitter complaints from Brezhnev about Carter's unilaterally arranging the Egypt-Israel treaty after signing a joint communique that pledged Soviet-U.S. cooperation on the Middle East in October 1977.

SALT - the only area in which the Russians feel progress has been made with the Carter administration - Has taken on an overwhelmingly symbolic importance in the Soviet-U.S. relationship. It is perhaps too important to the Russians to be put through the kind of ideological prism that still seems to dominate thinking on regional conflict.

This split-level forecast of Russian concerns emerges in part from public statements made by Soviet visitors and a joint communique released after a three-day conference last month in Williamsburg in which 17 Russians and 23 U.S. citizens discussed SALT, economic cooperation. Africa and the Middle East in four working groups.

Known as the Dartmouth Conference, the gathering has taken place 12 times since President Eisenhower suggested in 1958 that a continuing private dialogue could help ease the Cold War. The Russians were among their nation's top experts on the United States and were sponsored by Georgi Arbatov's Institute of U.S. and Canada Studies. The Americans were all private citizens.

The shape of this year's Dartmouth conference discussions strongly suggested that, going into the summit, the United States and the Soviet Union possess shared goals when it comes to slowing the nuclear arms race an in building economic bridges to each other.

Delegates reflected a consensus that a successful summit and approval of SALT II in the Senate would put U.S.-Soviet relations in the strategic and economic fields on a stable course during an otherwise volatile time of change in Soviet leadership.

But translating the relative harmony at the strategic and economic level down to a meaningful dialogue on moderating regional conflict still appears to be a distant goal in all levels of Soviet-U.S. talks.