On the eve of an important round of U.S. Soviet negotiations on limiting strategic arms, the Carter administration's senior adviser on Soviet affairs said yesterday that relations between the superpowers may have stopped deteriorating and could be headed up again.

Marshall D. Shulman, special State Department adviser on Soviet affairs, told a House subcommittee that the United States has recently been taking "measured steps" to take account of several favorable moves by Moscow in recent weeks, and he suggested that additional Soviet movement in politically sensitive areas will bring additional U.S. responses.

The strategic arms limitation talks (SALT), which deal with the nuclear balance of power at the heart of the relationship, are scheduled for another round at a high political level today in New York. A U.S. delegation headed by Secretary of State Cyrus R. Vance is to meet a Soviet delegation headed by Foreign Minister Andrei A. Gromyko to hear Moscow's answers to the latest Washington proposals.

Shulman said yesterday that a SALT II agreement is "perhaps 95 percent" complete, and that there has recently been some narrowing of differences on the few outstanding issues remaining. "It is possible that agreement could be reached in the near future," he said.

Senior U.S. officials have expressed the belief that President Carter's success in winning Egyptian-Israel agreements at Camp David has improved the prospects for early conclusion of a SALT treaty, largely because Carter's enhanced popularity and reputation for diplomatic competence make Senate approval of a treaty more likely. But officials have also said that much depends on Russian willingness to make concessions on the final outstanding issues.

In his testimony to the House International Relations subcommittee on Europe and the Middle East. Shulman dated the downturn in U.S.-Soviet relations from late 1975, when the Russians intervened in Angola, and said that additional African operations, growing Soviet strategic and conventional military power and police crackdowns at home contributed to the deterioration.

With "fingers crossed." Shulman said the downturn might have bottomed out in midsummer. "During the August holidays, a lull in the chain of actions and reactions gave both sides an opportunity to reflect on the consequences of the momentum that had been building up in the downward spiral," he said.

Shulman said a number of recent Soviet steps suggest that Moscow wishes to reverse the tide. He cited:

Terminating court action against Hal Piper of The Baltimore Sum and Craig Whitney of The New York Times, who were charged with slander "as part of an effort to limit western reporting on Soviet dissidents." Shulman said that, as a result, possible U.S. retaliatory action against Soviet news correpondents here has been dropped.

Ending the travail of Jay Crawford, the International Harvester Co. representative in Moscow who was allowed to leave the country "after a transparently contrived trial" for currency violations. Shulman told reporters that, as a result, the United States has begun to ease retaliatory restrictions which had been imposed on visas for Soviets seeking to make business deals here.

Reducing "the inhumane severity" of some recent human rights sentences, and allowing a continued high rate of Jewish emigration - about 23,000 a year, the highest since 1973. Shulman said the emigration rise may be "a signal" that the Soviets wish to see an easing of trade restrictions imposed by Congress tied to the emigration issue.

Soviet acquiescence in a more constructive role by Angola in its relations with Zaire and Namibia, and "certain limitations" observed in Ethiopia. Shulman told reporters that the latter included Soviet restraint in Eritrea and apparent Soviet influence on Ethiopia's decision not to invade Somalia and to limit the bloodshed in the Ogaden region.

Shulman saw some signs that the Soviets have used their influence to counsel caution among Arabs in the Middle East, though he also said he believes the Russians have not decided what to do in the present circumstances. He said their major complaint about the Camp David decisions is that they are excluded from any role in the region.

Rep. Lee Hamilton (D-Ind.), the subcommittee chairman, pointed out that the United States and Soviet Union agreed formally last Oct. 1 that negotiating within the framework of the Geneva conference is "the only right and effective way" to solve the Arab-Israeli dispute. Asked if the United States did not totally reject that approach at Camp David. Shulman said that Washington does not believe the Russians fulfilled their part of the Oct. 1 bargain, and a Geneva cconference remains an ultimate U.S. goal.