Israel has agreed to leave all of its civilian installations in southern Sinai intact when it evacuates the peninsula next April and return it to Egypt, Israeli Prime Minister Menachem Begin told his Cabinet today.

Reporting on his talks Thursday with Egyptian President Anwar Sadat in Sharm al-Sheikh, at the southern tip of the Sinai, Begin said his agreement was conditioned on the station of U.S. personnel in the proposed multinational peacekeeping force in the Israeli-developed town of Ophira, just south of Sharm al-Sheikh. Cabinet sources said Sadat had accepted the condition.

Begin is said to have told the Cabinet that the U.S. members of the peacekeeping force would assure Israel unrestricted shipping access through the Strait of Tiran, connecting the Gulf of Aqaba and the Red Sea. An Arab blockade of the strait touched off the 1967 Middle East war.

Sadat and Begin also reportedly agreed Thursday that half of the Sinai peacekeeping force will be U.S. personnel. The force, which is to patrol the Sinai as part of the Egyptian-Israeli peace treaty, is scheduled to be in place when Israel returns the final third of the Sinai Pennisula, which it seized in the 1967 war.

The civilian installations in Ophira include hotels, restaurants, a marina, stores and homes built by about 120 families. During a tour of Ophira Thursday, Sadat told Begin the settlers had "performed a most praise-worthy feat" in developing the town.

But the Egyptian leader also told Begin and a group of settlers that they must evacuate the town before the turnover and that Egypt will then consider their requests if any want to return for an Egyptian firm that will operate the resort area.

Sadat reportedly agreed to construct a new road from the Israeli town of Eilat, at the northern end of the Gulf of Aqaba, to the Etzion air base in the Sinai. It is to be converted into an Egyptian civil aviation facility and Israel has been assured access.