Egyptian President Anwar Sadat, after lengthy talks with President Carter, yesterday rejected Carter's suggestion that Israel be permitted to maintain defense lines beyond its sovereign borders in a Middle East peace agreement.

"We have discussed this," Sadat told a news conference on the final day of his Washington visit. "[But] sovereignty is indivisible, and we can't have two borders. There is always one border for any country."

While acknowledging differences with Carter on this and other issues, Sadat displayed optimism that a new Geneva conference on Arab-Israeli peace will be convened within 1977. Saying he and Carter have agreed "not to waste time," the Egyptian leader called for the United States to begin preparations for the substantive negotiations at Geneva.

Washington sources said Sadat has become concerned that an ill-prepared Geneva conference might break down quickly after being convened, deflating the hopes of moderate Arab leaders and their constituencies and thus encouraging new wars and internal upheavals. He said a U.S. task force headed by Secretary of State Cyrus R. Vance would be the best means to make preparations for Geneva, and hinted that such a group is already planned.

The first of a succession of Arab leaders scheduled to visit Carter, Sadat is considered to be among the most flexible. He is also the one most personally committed to a settlement, with his prestige and perhaps his continued rule riding on early progress towards peace.

Sadat's reactions to the new U.S. President and his ideas have been keenly awaited here and in the Middle East. Publicly he praised Carter yesterday as "a very dear friend" in whom he has "full confidence." Privately Sadat told Arab diplomats late Tuesday that while he worried about Carter before coming here, he emerged from the White House meetings very satisfied with personal rapport and confident that he did not bet wrong in his strategic shift from a Russian to an American connection.

As in private meetings with Carter and members of Congress, Sadat expressed concern to reporters about Soviet activities in Africa. He portrayed Egypt, which was formerly a Russian ally, as an anti-Communist bulwark on the fringe of Africa and declared that "the United States as a friend has a moral obligation to help me, not by sending American soldiers but by other means."

Sadat did not specify the "other means," but appeared to be speaking of the "defensive" military hardware, including F-5E warplanes and armored personnel carriers, that he discussed with U.S. officials here. The weapons issue "is still open" at the conclusion of his visit, he said.

American officials conceded that no gaps had been closed between Egypt and Israel on the substance of a Middle Eastern settlement during the Sadat-Carter conversations. But they expressed satisfaction with the tone and what they described as the detailed nature of the talks, and said Sadat would leave Washington with concepts and suggestions to ponder.

The Egyptian leader, in his press conference, urged again that the United States undertake a dialogue with Palestinian leaders, saying that "without the Palestinians we can't establish peace." While denying a report in the Middle East that he brought a written message to Carter from the Palestine Liberation Organization, Sadat pointed out that he met several times with PLO Chairman Yasser Arafat before coming to Washington.

The Carter administration has refused to recognize or negotiate with the PLO until that organization recognizes Israel's right to exist, in keeping with a written commitment given to Israel by then-Secretary of State Henry A. Kissinger in September, 1975.

The Cairo newspaper Al Ahram reported yesterday that Sadat has convinced Carter of the need of PLO participation in the Geneva negotiations and for the need for establishment of "a Palestinian state, United Press International reported. However, Sadat made no such claims in his press conference, although he restated his belief that the Palestinian question is "the core of the whole problem." Al Ahram also reported that Sadat invited Kissinger to make a return visit to Egypt as a private citizen during a meeting of the two men Tuesday.

On other elements of a possible Middle Eastern settlement, Sadat told reporters:

He and Carter discussed the possibility of "demilitarized zones on a reciprocal basis." This is in keeping with a long standing Egyptian position that any demilitarization apply both to Arab and Israeli sides.

"Everything will be normalized" between Israel and its Arab neighbors following a comprehensive settlement that is signed between them.

In response to a question from an Israeli journalist, Wolf Blitzer of the Jerusalem Post, Sadat said the Egyptian people are not yet ready for visits from the Israeli press because of the 29 years of bitterness and hatred, including four wars. "We must take it gradually. Whenever we end the state of belligerency in the peace agreement which is supposed to be signed in Geneva, I think all this will be very easy," Sadat said.

The Egyptian leader also asked that Egypt not be asked to trade with Israel by the written terms of a peace agreement. He drew laughter by conceding that Egypt is in "an economic mess" and said that Israel is "in a bad position like me."

Egypt has severe economic problems and, like Israel, is afflicted with large deficits because of heavy military spending.