The United States yesterday kept up pressure on the Palestine Liberation Organization to expel radical commander Mohammed Abul Abbas from its executive committee, threatening to veto Arab calls for another special session of the U.N. General Assembly in Geneva, a senior U.S. official said.

At the same time, the official said, the United States will give PLO chairman Yasser Arafat more time to denounce the Abul Abbas group's thwarted seaborne guerrilla attack on Israel last week before moving to break off a dialogue with the Palestinian umbrella organization.

The PLO executive committee meets today and administration officials said they would watch the outcome closely.

"Given that the dialogue with the PLO is clearly in jeopardy, we want to provide sufficient opportunity for Arafat and the other PLO leadership to do what we've asked them -- to disassociate from the attack, to condemn it and to take steps to take Abul Abbas off the executive" committee, the official, who asked not to be identified, told reporters.

State Department spokesman Margaret Tutwiler has described as "horrifying and outrageous" the attack last Wednesday, in which two groups traveling in speedboats -- apparently from a Libyan mother ship -- tried to land on crowded tourist beaches along the Mediterranean. Israeli defense forces killed four gunmen and captured 12 others.

Abul Abbas's group claimed responsibility, saying the attempted strike was aimed at avenging the mass murder of seven Palestinians by an Israeli gunman near Tel Aviv on May 20.

Tutwiler said yesterday U.S. Ambassador to Tunisia Robert Pelletreau has met three times this month with PLO officials to discuss the incident.

At a press conference last week, Arafat distanced himself from the attack, but stopped short of condemning it or disciplining Abul Abbas, who he said was elected by the Palestine National Council, the Palestinian parliament-in-exile.

One of Arafat's senior deputies, Khaled Hassan, executive committee member for Fatah, the largest PLO faction, criticized the raid for ignoring Israeli radar capabilities. He said Abul Abbas "did not consult or confer with the executive committee {on} whether it was acceptable to carry out a military operation. . . "

But an Israeli official said yesterday that Israel is certain the attack plan was developed "over many, many months" by Abul Abbas, who wanted a big operation that would draw international attention. The official said Israeli monitoring suggested the attack would come by sea, but he said there was no indication of the timing or what kind of ships would be involved.

The Israeli official said Israel is now weighing a response to the attempted raid that will not necessarily be a dramatic attack, so as not to provoke a regional response. But "someone has to pay a price for this," he said.

Staff writers Patrick E. Tyler and Al Kamen contributed to this report.