Prime Minister Yitzhak Shamir today directly accused Syria of being responsible for the bomb attacks on the headquarters of the U.S. Marines and French paratroopers in Beirut Sunday.

Shamir made the accusation, the most direct leveled by any senior Israeli official since the bombings, during a private meeting with leaders of the Israel Bonds organization. His office later made public a partial text of the remarks.

"We know who was behind the criminal attacks in Beirut, in which hundreds of American and French soldiers, sent to Lebanon to keep the peace, paid with their lives," the prime minister said. "It was perpetrated by Syria and by terrorist elements acting under its aegis and enjoying an umbrella of Soviet protection."

Following the bombings, Israeli officials were quick to point to Syria as a likely culprit and argued that it would have been impossible to mount the precision, suicide attacks on the military headquarters without at least Syrian complicity. Shamir's accusation today appeared to go beyond these earlier assertions, although it could not be determined whether he based his statement on recent information gathered by Israeli intelligence agencies.

U.S. officials have said they have some indications of who was responsible for the attacks, but they have refused to discuss this publicly. Speculation has centered not only on the Syrians but also on radical Shiite Moslem factions aligned with Iran.

In his statement to the bond leaders, Shamir strongly supported President Reagan's vow to keep the Marines in Lebanon as long as necessary.

The subject of Israel's future role in Lebanon is expected to be high on the agenda when a U.S. diplomatic mission headed by Undersecretary of State Lawrence Eagleburger and Assistant Secretary of State Richard W. Murphy visits here next week. The visit reportedly was planned before the Beirut bombings, but events have given it new urgency.

Israeli officials are known to be wary of suggestions such as that voiced this week by former secretary of state Henry A. Kissinger that the policy of the United States and other participants in the Beirut multinational force be more closely coordinated with the Israelis, who occupy southern Lebanon with a military force roughly twice the size of the multinational force.