What is believed to be the last body of the Americans killed in the Monday bombing of the U.S. Embassy here was pulled from the ruins this morning, shortly before Undersecretary of State Lawrence Eagleburger and a delegation from Washington arrived to escort the 17 dead home.

Rescue workers found the corpses of at least two Lebanese today and sighted what appeared to be the bodies of four others in the mail room off the front lobby of the embassy. But this evening demolition contractors and embassy staff were attempting to determine how they could be taken out without endangering the lives of rescue workers.

Sources here said today that marines had found parts of a heavy vehicle, possibly a pickup truck, which they believe carried the bomb, in the rubble.

Eagleburger, speaking briefly to reporters after he and the delegation from Washington inspected the ruins under heavy armed guard, said, "The assumption is, on the basis of the evidence so far, there was a van which drove into the embassy grounds and apparently drove up against the building and blew up."

Asked whether there would be an investigation to determine why the embassy was not protected by barricades, he said, "I am sure that we will seek for the lessons that can be learned from this experience."

But he added, "An American embassy is in a country to deal with the people of the country. It's not a fort. It's not a vault. We don't hide behind steel doors and peek out through peepholes. We have work to do and that happens to be dealing with the country in which we are assigned. Under those circumstances, it is a constant compromise between absolute security and being able to do a job."

Eagleburger discounted speculation that the attack was directed against a CIA analyst who was visiting here on business from Washington and killed in the blast, but he did not discuss who might have done it or why.

The undersecretary for political affairs met with Lebanese President Amin Gemayel to express the "horror and outrage at the cowards that perpetrated this act."

"I also emphasized to him," Eagleburger said, "at the behest" of President Reagan "that what's been done here will not in any way prevent the United States from carrying forward with its objective of a free Lebanon, a withdrawal of all foreign forces from the country--a country that is sovereign within its own territory."

The plane escorting the bodies back to the United States is to leave here early Saturday. It will be met on arrival at Andrews Air Force Base by President Reagan and other high-ranking officials.