Sol Linowitz, the former U.S. special envoy to the Middle East, said today that Egyptian and Israeli officials had changed their respective positions only slightly regarding Palestinian autonomy but that he was optimistic at the prospect of an agreement.

After meeting with Israeli Foreign Minister Yitzhak Shamir, Linowitz told reporters he had a message from Egyptian President Hosni Mubarak to deliver Thursday to Prime Minister Menachem Begin. He said it deals with "substantive" issues but would not elaborate.

Linowitz, who arrived here from Egypt, had been invited by President Anwar Sadat to tour archeological sites with his family. After Sadat's assassination, he said, Mubarak renewed the invitation for the "private" visit.

Israeli officials said there was "nothing operational" about Linowitz's visit. However, they said, the former special ambassador to the autonomy negotiations briefed Shamir about his experiences and his impressions of Egyptian positions on self-rule for the 1.2 million Palestinians of the occupied West Bank and Gaza Strip.

Meanwhile, Israeli officials told Reuter that Begin sent a letter to President Reagan Tuesday saying that recent statements by Egyptian Foreign Minister Kamal Hassan Ali, his deputy Butros Ghali and Egypt's semiofficial press contradict the Camp David accords.

These statements spoke of self-determination for the Palestinians and East Jerusalem, which Israel firmly opposes.

Linowitz, who said he would report to U.S. Secretary of State Alexander M. Haig Jr., said that he had found an "unequivocal" commitment in Mubarak to the Camp David peace process and that Shamir "believes in the importance of accelerating the pace and trying to reach an agreement."

He added, "I think there is some modification of positions. It's hard to judge how much at this juncture . . . . But in my judgment, there is enough progress so that there should be a more intensified effort to reach a solution."