Former president Jimmy Carter will attend Egyptian President Anwar Sadat's funeral in Cairo Saturday whether he is a member of the official U.S. delegation or not.

That's the word White House deputy chief-of-staff Michael Deaver got last night at the Moroccan Embassy, where the new U.S. ambassador-designate to Morocco, Joseph Verner Reed Jr., and his wife Mimi were the guests of honor.

Deaver was also told by a former senior official in the Carter administration that President Reagan would be well advised to lead the American delegation and avoid making the mistake Carter did when he decided against attending the funeral of Yugoslavia's Marshal Josip Broz Tito last year.

Deaver said no decision had been made yet about who will represent the United States but that a meeting is scheduled for today. Another White House aide said the delegation would include "very high-level" Americans.

When Deaver voiced concern for President Reagan's safety, the former Carter aide assured him that the White House's security officers could handle that. The aide said Reagan's presence at the services would reassure Egypt of U.S. support at a time when such public display is essential.

The assassination of Sadat dominated the conversation at last night's dinner, given by Moroccan Ambassador Ali Bengelloun and his wife, Jackie. Bengelloun, in his toast, called it a "tragic day" and described how Morocco's King Hassan II had telephoned Egyptian Vice President Hosni Mubarak to offer condolences, despite strained relations between the two countries.

Former CIA director and ambassador to Iran Richard Helms, though, saw yesterday's tragedy as perhaps "an opportunity for other Arab countries -- the moderate ones who are not cheering his death like Jordan, Morocco, Algeria and Saudi Arabia -- to identify now with other Moslems in this moment of grief.

"They do tend to turn together at those times, and this may be an opportunity for Egypt to end its isolation," he said.

Helms said he did not think it was a "great surprise" that Sadat was assassinated. "After all, there was the possibility he would be assassinated ever since he became president of Egypt. And anyone who had as many enemies as he did faced that danger."

But what surprised Helms and others at the dinner was that Sadat had not been better protected by Egyptian security forces and that he was not wearing a bulletproof vest.

"I don't quite understand that, because certainly Egypt's security officials were aware that many people wanted to kill him," Helms said.

When a senior White House official said Sadat had been shot in the head, someone else threw up his hands and said that a bulletproof vest wouldn't have helped under those circumstances.

Ambassador-at-large Vernon A. Walters said Sadat knew how to choose men and "he chose his vice president well. I hope he will give Egypt and the rest of the area the stability it needs so much. If you have a strong man in Egypt succeeding Sadat, there's a good chance that the peace process can go forward."

On AWACS, Senate Foreign Relations Committee chairman Charles Percy (R-Ill.) said he told President Reagan yesterday that Sadat had felt strongly about the radar planes' sale being in the best interests of not only Saudi Arabia but also of Israel and the United States as mediator in the Middle East.

"He told our committee that if we had not sold jet aircraft to Egypt when we did, there never would have been a Camp David," said Percy.

For his part, Ambassador-designate Reed grew reminiscent in his after-dinner remarks about a visit to Cairo a few years ago when the shah of Iran was looking for a place to stay.

But Reed, a vice president of Chase Manhattan Bank and a key adviser to David Rockefeller, told the 50 formally clad dinner guests that what he was saying was off the record. This, despite a newspaper report sent out by his office in a predinner publicity package saying that he played an important role in getting Sadat to give refuge to the shah.

The guest list was a cross section of past and present official Washington and included Zbigniew Brzezinski; Richard Nixon's chief of staff, L. Nicholas Ruwe; Reagan aides Joseph Canzeri, Peter McCoy, Phyllis Kaminsky and Helene von Damm; Bendix executive Nancy Reynolds; Tunisian Ambassador Ali Hedda; Smithsonian Institution Secretary S. Dillon Ripley; Sen. Russell B. Long (D-La.), and two former ambassadors to Morocco, Angier Biddle Duke and Robert Anderson.