About 600 members of the world's oldest continuing Jewish community had gathered in an upstairs room carpeted with Persian rugs at the Central Synagogue for Sabbath services.

Yet amid the traditional greetings of shalom (peace), there was a heavy atmosphere of unease engendered by a recent spate of anti-Semitic leaflets, posters and rumors.

Tehran's Jews understandably are deeply apprehensive about what the uncertain political future holds for them in this overwhelmingly Moslem country.

Whatever their personal attitude toward Shah Mohammad Reza Pahlavi, those gathered at the synagogue were aware that the Pahlavi rule has guaranteed the 75,000 Iranian Jews both religious freedom and personal safety.

"We've had 50 years of security," said a 30-year-old engineer, sitting before a blue silk covered torah, "but we don't know what our fate will be if the shah is replaced by a strictly Islamic regime. So, many of us therefore are leaving -- or thinking of leaving."

Cantor David Shofet, 39, who studied Hebrew theology in Israel and in New York City, urged calm upon his congregation, all of whom were wearing hats or yarmulkes . The women sat apart from the men during the services.

"We've been here for 2,500 years," Shofet said after the service. "We are like other Iranians, and the people here have been good to us. But it's difficult to foresee the future because things are changing so fast.

"I don't think the Iranians would be against Jews as Jews," he added. "Under the Iranian law we are a protected minority."

Shofet's father, Yedidya, is the rabbi of the congregation and he, too, asked for cool reticence, declaring that at present there is no reason for Iranian Jews to panic.

Jews have been in Iran since before the destruction of the First Temple in Jerusalem nearly 2,500 years ago. Cyrus the Great, the first Persian monarch, freed the Jews from their Babylonian captivity in 539 B.C.

By the end of World War II, the Jewish community totaled about 200,000, but about half of them left Iran -- mainly for Israel -- at the time of that country's independence in 1949.

Today, 75,000 Jews remain in Iran, mostly concentrated in Tehran, but substantial communities also exist in Shiraz and Isfahan.

"They are of the Sephardic tradition, mainly Orthodox," an Israeli observer said. "But to me their services seem more like Reform Jewry."

In addition to the Central Synagogue, about 80 smaller ones are scattered in various parts of Tehran, according to Jews here. About a dozen Jewish schools, which almost all Jewish children attend, have also been established.

What worries the Jewish community are leaflets and all wallposters that carry warnings to Jews. One of these on a Tehran street said: "Death to Jews and Bahais," a large sect in Iran.

These messages in turn, provoked various kinds of rumors about more threats against Jews in Iran.

Other statements reportedly made by Moslem leaders in dicated that they are not antipathetic toward Jews themselves, but only Zionists. That is scant comort to the Jewish community, most of whose members are sympathetic to Zionism.

The Jews are also upset by statements attributed to Ayatollah Ruhollah Khomeini, the exiled Shiite Moslem leader, that a new government here would cease exporting oil to Israel and possibly break off diplomatic relations with Israel. Israel receives 60 percent of its oil supplies from Iran and has done about $100 million worth of business with Iran in recent years.

Israeli diplomats here express comcern about the situation but say there is no reason for panic, at least not yet. They estimate that 8,000 to 10,000 Jews have left Iran since the violence in the streets increased two months ago.

El Al, the Israeli national airline, has been flying five flights a week between Tehran and Tel Aviv, and many of the planes have departed fully loaded.

Most Iranian Jewish families have relatives living in Israel, yet Israeli officials say that only 600 Iranian Jews have formally sought permission to go to Israel. Instead, most of the departing Jews are heading for Europe and the United States, particularly Los Angeles, which has a large Iranian and Jewish community.

Iranian Jews have prospered here during the past 20 years. Most are middle-class merchants, lawyers, doctors and academics. The Tehran Association of Jewish Physicians, for instance, has 600 members.

Jewish merchants also have played a key role in the commercial life of the capital, involved in import and export businesses and in the trade of the bazaar, the business nerve center of Iran. Many are involved in the important carpet trade.