MOSCOW, AUG. 20 -- U.S. Sen. Daniel Patrick Moynihan (D-N.Y.), heading a four-member Senate delegation here, said today U.S. restrictions on Soviet trade will be lifted only when all Soviet Jews who want to leave the country have been given permission to emigrate.

Until the Soviet Union recognizes the "normalcy" of emigration, the issue will remain "a barrier to acceptance of this as an open society," the New York Democrat said at a delegation press conference for Soviet and foreign journalists.

Although the number of emigrants allowed to leave the Soviet Union has taken a sharp upward turn this year, Moynihan said that the numbers are still small compared to levels reached in 1979, when a wave of emigration by Soviet Jews peaked at 51,000.

In 1974, the U.S. Congress tied the lowering of tariffs on Soviet imports by the United States to a relaxation of Soviet emigration policy. Moynihan today said a repeal of the 1974 Jackson-Vanik Amendment was possible "when it is established by the community involved that those who wish to leave have left."

According to Israeli figures, the number of Soviet Jews who wish to emigrate is 400,000, but Jewish activists in Moscow put the number closer to 40,000. Moynihan told reporters today that the true number will become apparent when all restrictions on emigration are lifted by Moscow.

Soviet officials this week said that a total of 15,000 people have been given exit visas in the first seven months of this year, although not all have left yet. So far, western relief agencies have reported the arrival of 3,900 Jews in the West this year, almost four times the number who left in all of 1986. The numbers of other emigrants -- including Germans and Armenians -- have also been on the rise.

Moynihan said Soviet officials indicated that Moscow had reviewed its attitude toward emigration, which had slowed almost to a halt last year. "They say the issue is resolved as a matter of policy," he said. "We would have to see it as a matter of practice."

At the press conference today, Sen. Paul Sarbanes (D-Md.), said another test of Soviet commitment to more open emigration was the dozen remaining cases of Soviet citizens married to Americans and denied exit visas to live with their families in the United States.

"There is a necessity to translate statements into practical reality," he said. "Apparently, this is encountering difficulty."

The group, also including Sens. Terry Sanford (D-N.C.) and Mitch McConnell (R-Ky.), has met with a range of Soviet officials, including Moscow City Communist Party chief Boris Yeltsin, an alternate member of the Politburo.

According to the New York Democrat, some Soviets had expressed "manifest concern" that the United States would seek to block the reform process begun by Soviet leader Mikhail Gorbachev. "We gave them firm assurance that that in no way should be deemed an American interest, still less is it an American policy," Moynihan said.

Members of the delegation said they were leaving Moscow impressed by the new "openness" apparent in their dialogues with Soviet officials.

The senators said they were leaving cautiously optimistic about the prospects for a summit between Gorbachev and President Reagan, which now depends on progress at the negotations in Geneva on a treaty eliminating medium- and short-range nuclear missiles. The main obstacle, they said, remains a resolution of the status of U.S.-held nuclear warheads on 72 Pershing IA missiles in West Germany.

In recent statements, Soviet spokesmen have cited U.S. refusal to move on the issue of the Pershing IAs as the reason for a stalemate in Geneva. Without progress in Geneva, the planned meeting in September between Secretary of State George P. Shultz and Soviet Foreign Minister Eduard Shevardnadze may not be "expedient," said Viktor Karpov, head of the Foreign Ministry's Disarmament Department, in an interview with the Soviet news agency Tass.

At a press briefing today, Soviet Foreign Ministry spokesman Gennadi Gerasimov said the American attitude "causes some doubt on what we will have, come September." At present, he said, "everything is standing still except the calendar."