JERUSALEM (AP) _ The presidents of the West German and East German parliaments said today they had won Israeli assurances that the Jewish state will support German unity.

The understanding appeared to include a promise that a united Germany will back Israel in its conflict with the Palestinians and use its considerable influence to tone down growing European Community criticism of Israel.

Israeli Prime Minister Yitzhak Shamir ''gave us an unconditional yes to reunification,'' Rita Suessmuth of West Germany told reporters at the end of a three-day visit with her East Germany counterpart, Sabine Bergmann-Pohl.

Shamir spokesman Avi Pazner said the prime minister ''does not oppose reunification.''

Shamir also told the visitors he expected a united Germany ''to influence other members of the European Community to adopt a more understanding attitude toward Israel,'' Pazner said.

The two presidents indicated they were ready to meet the expectations. Throughout their trip to Israel, they reiterated the importance of Israel's right to exist in secure borders but did not mention Palestinian demands for self-determination. They had no meetings with Palestinians.

Ms. Suessmuth today also referred to a new European Community declaration accusing Israel of violating human rights of Palestinians in the occupied West Bank and Gaza Strip and denouncing Jewish settlements in those areas.

''Calls for protection of human rights make no sense if we don't deal first with Israel's right to exist,'' Ms. Suessmuth said.

The Foreign Ministry today rejected the European Community leaders' criticism as ''unbalanced.''

Also today, an Israeli immigration official said a slowdown in immigration of Soviet Jews this month might reflect a change in Soviet policy that had been threatened by President Mikhail S. Gorbachev.

Boaz Shviger, a spokesman for the quasi-governmental Jewish Agency, which assists in settling immigrants, said the rate of immigrant arrivals stopped growing in June.

''At this point I wouldn't say it is (Soviet) policy,'' he said in a telephone interview. ''It is still too early to decide. However, I would be careful not to rule it out either.''

A Jewish Agency official who requested anonymity said immigrants traveling through Vienna this month had complained that unofficial Soviet government orders were delaying exit visas.

In a news conference in the United States on June 3, Gorbachev said the Soviet Union ''is being bombarded by a lot of criticism'' from Arab states over some of the Soviet immigrants settling in the occupied West Bank.

Gorbachev added that if Israel does not reconsider its policy, ''We must give further thought to it, in terms with what we can do with issuing permits for exit.''

Prime Minister Yitzhak Shamir has tried to reassure the Soviet Union by saying that Israel does not direct immigrants to the territories. On the other hand, he said Israel cannot block them from moving where they want.

''Everybody in a democratic country has a right to settle wherever he wishes,'' Shamir told Israel radio on Tuesday.

Arab states and local Palestinians say they fear settling Soviet immigrants on war-won land could force out Palestinians and undermine their efforts to gain an independent state. The territories, home to 1.7 million Palestinians, were captured by Israel from Jordan and Egypt in the 1967 Middle East war.

Ida Ben Shitrit, spokeswoman for the government's Absorption Ministry, said 8,405 Soviet Jews arrived in Israel during the first 26 days of June. At that rate, June's total will be about 9,700, down nearly 600 from May.

Before June, immigration figures showed persistent growth, hitting a record 11,028 in April. May's lower figure of 10,293 was a result of problems with transit flights from Europe, the officials said.

Meanwhile, the Israeli army today began to deploy more troops along major roads in the occupied lands to try to reduce Palestinian stoning attacks on military patrols and on the cars of Jewish settlers.