A U.S. Marine spokesman said today that "infiltrators" posing as rescue workers had been discovered around the wreckage of Sunday's bomb explosion that killed 225 marines.

Marines suspected these terrorist agents might have been working with others preparing for a second bomb attack against marines, according to the spokesman, Maj. Robert Jordan. He said "several" such persons were turned over Tuesday to Lebanese authorities, although it was unclear what happened to the suspects.

Marines were still concerned today about reports that three trucks laden with explosives have been orbiting their perimeter in preparation for an assault similar to Sunday morning's car bomb attack against the Marines' Battalion Landing Team headquarters adjacent to the cargo terminal at Beirut International Airport.

Salvage operations at the bombed-out site continued today. Marines also worked to improve defenses and attempted to account for all the dead and missing. A list of those surviving the explosion, which marines began working on Tuesday night, was completed today.

Grief hung heavily over the compound today as Marine officers added details about the Sunday attack and troops lined up to use free telephone lines, made available by AT&T, to call home and assure relatives that they were unharmed.

"The mood of the men, the marines and sailors ashore, is one of quiet fury," said Col. Timothy J. Geraghty, the Marine commander.

He said flatly that the bombing had been "well planned and well coordinated" by "outside forces." He declined to identify the culprits.

Adding details to earlier versions of the attack, Marine officers gave secondhand accounts of eyewitness survivors who said a yellow Mercedes truck had circled the civilian airport parking lot adjacent to the Marine compound before charging past Marine sentry posts and smashing a heavy metal gate.

Initially, the Marine sentries did not suspect foul play. The truck was similar to produce vehicles often in the area. But when it raced toward the compound, sentries who were later evacuated for treatment of injuries indicated to officers, they knew what was happening.

One Marine guard, however, had no ammunition magazine in his rifle, according to the accounts.

Capt. Wayne Briggs, 28, of Charleston, S.C., was one of those still stunned by the morbid irony of his survival. Only a week earlier he had been transferred from the building where the explosion occurred to fill the slot of an officer who had been killed by a sniper.

Asked how he felt after the blast, Briggs, responding in an emotional, wavering voice, said, "Very lucky. My cards hadn't been dealt yet."