Prime Minister Menachem Begin, returning from a three-day visit to Egypt and talks with President Anwar Sadat, said today he had reached agreement with Sadat on Israel's purchase of oil from Sinai Peninsula fields it will relinquish as a result of the peace treaty.

Begin said Israeli's Alma oil fields, which recently have been producing up to 15 percent of the nation's oil consumption, would be formally turned over to Egypt on Nov. 26. The next day, Israeli oil tankers would stand by to receive shipments at the "world market" price, he said.

Begin's remarks dispelled reports that negotiations on oil sales to Israel, which are included in the peace agreement but not with specifics, had broken down. Begin said oil experts from both countries will work out details of the transfer and pricing, but he gave no indication that Israel would receive preferred prices for what it buys from Egypt. Begin also said an Israeli delegation will go to Cairo soon to meet with Egyptian transportation officials to discuss a proposal to rebuild the Cairo-Israel railroad. The rail line, part of the old Cairo-Beirut line, has not been used for more than 30 years.

Begin said representatives of Canadian Pacific Railways had expressed and interest in reviving the rail link, and that he and Sadat had agreed that the proposal should be explored by both countries. Calling the idea "practical," Begin conceded that opening the rail line could be years away.

Much of the track of the line was ripped up by the Israeli Army for use in the construction of the Bar-Lev defense line along the Suez Canal at the time of the 1973 war.

In an unexpected development, Begin flew today from Alexandria, Egypt, to Jerusalem's airport instead of Ben-Gurion International Airport, thus becoming the first Israeli prime minister to land here from a flight abroad.

Begin greeted family members and government ministers at a red-carpet reception. The small airport is in East Jerusalem, annexed by Israel in 1967 and Begin has said he will hold more receptions there to demonstrate Israel's intention to keep East Jerusalem,

Begin's Israeli-made executive jet landed at the East Jerusalem airfield several hours ahead of a press plane that also carried four members of an Egyptian Jewish family who were reunited with their brother, Robert Dassa, who served 14 years in an Egyptian prison for his involvement in an unsuccessful espionage plan in 1954.

Begin asked Sadat during the talks for permission for the family to visit Israel, and special orders were immediately written for travel papers.