President Carter's plan to sell Egypt 50 F5E fighter-bombers almost went down in flames because Egyptian President Anwar Sadat demanded so many sweeteners, administrative officials said yesterday.

Sadat, sources said, kept telling American officials that since the F5E was not as sophisticated a plane as the F15 fighter that the United States is selling to Israel and Saudi Arabia, he should receive some extras, such as better ground equipment to maintain the planes and more sophisticated gadgetry inside the cockpits.

"He wanted everything, including stereo," said one U.S. official facetiously.

Sadat's list of extras pushed the Carter administration's original advertised price of $400 million for the 50 planes up to around $700 million, more than Egypt's banker on deal, Saudi Arabia, was willing to pay.

The Egyptians and the Saudis were still haggling as Defense Secretary Harold Brown headed for the Middle East last week, for what he hoped would be a display of determination and unity by the United States and anti-communist nations in that part of the world.

After much pressure from U.S. officials, Egypt and Saudi Arabia agreed on a shorter list of extras, resulting in an agreed-upon compromise price of about $550 million for the 50 F5s and associated equipment. "Brown put the seal on the deal," said one official yesterday, during the defense secretary's recent talks in Saudi Arabia and Egypt.

Pilots do not consider the F5 any match for the F15, partly because the F15's radar is so much more powerful that it could see and shoot missiles at an F5 before the smaller plane knew it was under attack. The Carter administration has announced no plans to sell Egypt the F15.

Israel already has the F15, and Saudi Arabia is scheduled to start receiving the first of 60 F15s in 1981.