Egyptian President Anwar Sadat, in the afterglow of his warm reception in Haifa, feels peace with Israel has reached a point of no return guaranteeing triumph over even the thorny issue of Palestinian autonomy, special U.S. envoy Robert Strauss said today.

"He has a certain and secure feeling about the inenvitability of success," Strauss said in describing the mood in which he found the Egyptian leader during their discussions here last night.

Sadat's outlook coincides with Strauss' assessment that it would be a mistake to impose difficult decisions such as the future of Jerusalem or Palestinian participation on Egypt and Israel at this stage of the autonomy talks. An attempt last month to draw West Bank Palestinians into the negotiations through an American-proposed U.N. resolution failed because of opposition from Sadat and Begin.

Strauss emphasized, however, that sometime around the first of next year the disagreements will have to be faced. Under the treaty, autonomy elections for the West Bank and Gaza Strip are to be set up by the end of May. "We're going to start pushing harder on these issues, a lot harder," he said.

Between now and then, Strauss said, he intends to become more closely involved, in the autonomy talks.So far, he has left most of the actual U.S. negotiations role to his principal deputy, Ambassador James Leonard.

There was no indication, however, that Strauss plans to participate in the next plenary negotiations sessions, scheduled for Sept. 25 at Alexandria, Egypt.

Strauss spent more than three hours today with Egyptian Prime Minister Mustafa Khalil, "talking hard," he said, on the whole range of contentious issues facing the negotiators.