Two Soviet Jewish activists freed from prison in a secretly negotiated U.S.-Soviet exchange arrived today in Israel to a rousing welcome.

Among those at the airport to greet Edward Kuznetsov and Mark Dymshits were five other recently released Soviet Jews who arrived in Israel yesterday. Dymshits and Kuznetsov flew here from New York, where they and three other dissidents were exchanged for two Soviet spies last Friday.

An Israeli freighter, meanwhile, became the first known vessel flying the Israeli flag to pass through the Suez Canal. The trip of the 4,500-ton Ashdod down the 101-mile waterway was hailed as a new indication of peaceful relations between Egypt and Israel.

In the Tel Aviv ceremony, Kuznetsov's brother-in-law, Wolf Zalmanson, welcomed the new arrivals in Hebrew, saying, "As a new immigrant and now an Israeli of one day's standing, I can testify to the beauty of the country of which we dreamed while in Soviet prison."

Prime Minister Menachem Begin, who came to the airport to welcome today's arrivals, thanked President Carter, senior U.S. officials and world Jewry for helping secure the release of the Jewish activists.

The seven who arrived yesterday and today were in a group of Jewish activists who tried to hijack a plane out of the Soviet Union in 1970. Three are still in Soviet prisons.

[Dissident Physicist Andrei Sakharov said in Moscow that he had appealed to Soviet President Leonid Brezhnev to free the last three, Reuter reported.]

Dymshits expressed hope that the struggle would continue so other Jewish political prisoners would be freed and Jews wishing to come to Israel would be allowed to leave the Soviet Union.

"We did not feel lonely while in prison, for we knew that world Jewry and many other friends were supporting us," Kuznetsov said.

The Ashdod's journey through the Suez Canal was a milestone in the normalization of relations under the Israeli-Egyptian treaty, which guarantees Israeli ships unhindered passage through the canal. The treaty went into effect last Wednesday with the exchange of ratified documents.

The Ashdod, following the custom of the Suez, flew Israeli and Egyptian colors as it began its northbound passage at Suez City, the southern entrance to the canal. It had come from the Israeli port of Eilat on the Gulf of Aqaba and was on its way-empty-to the Israeli port of Haifa on the Mediterranean.

About 100 jubilant Egyptians, including soldiers and civilians waiting to cross the canal to the Sinai Desert, waved and cheered in Arabic, "Salaam! Salaam!" or "Peace! Peace!" as the freighter steamed past. The 22-man crew shouted back, "Shalom! Shalom!" the Hebrew word for peace.

Although no ship flying the Israeli flag has been known to pass through the Egyptian-owned canal, Israeli shipping officials said several Israel* i-owned vessels whose ownership was hidden have passed through flying "convenience flags."

Reports from Tehran said, meanwhile, that Iran broke diplomatic relations with Egypt, the first nation to harbor the exiled shah, and sources predicted that Tehran would soon exchange ambassadors with Libya, an arch-foe of Cairo.

Egypt accused Iran of bowing to pressures from Arab states opposed to the Egyptian-Israeli treaty, expressed regret at its action, and said Cairo also would break relations with Tehran.

Iran's move made it the first non-Arab country to break ties with Egypt since the peace treaty was signed. The new Moslem leadership under Ayatollah Ruhollah Khomeini expelled Israeli diplomats in mid-February and turned over the Israeli Embassy in Tehran to the Palestine Liberation Organization. CAPTION: Picture, Prime Minister Menachem Begin greets Mark Dymshits, left, and Edward Kuznetsov, center, as the two recently freed Soviet Jewish dissidents arrive in Tel Aviv yesterday to an emotional welcome come ceremony from Israelis. AP