Egypt today basked in the reflected glory of President Carter's brief morale-boosting meeting with President Anwar Sadat.

But in the light of past disappointments, officials expressed some doubts about Carter's willingness to make good his implicit commitment to press Israel for concessions, especially on the key issue of self-determination for the Palestinians.

Despite Sadat's insistence on the necessity of keeping up the momentum for peace - a view Carter shared in a carefully worded statement issued after the meeting in Aswan - Egyptian officals conceded they expected no sudden breakthrough.

Nor were Egyptians encouraged by reports that Israelis broke ground today for new settlements in the northern Sinai, just a day after Sadat said even the existing Israeli presence there could not be tolerated if there is to be a peace agreement. Past American complaints to Israel about new settlements in occupied Arab land have had no visible deterrent effect.

As a result of the failure of the Ismailia summit conference between Sadat and Israeli Prime Minister Menahem Begin, Egyptian officials appear reconciled to long-ardmous negotiations when direct talks resume at foreign minister level Jan. 15 in Jerusalem.

The key stumbling block involves Israeli reluctance to endorse Egyptian - and apparently American - requests for a declaration of principles that constitutes proof of Sadat's commitment to a comprehensive peace settlement acceptable to his Arab critics.

The most difficult aspect of the declaration touches on some form of self-determination for the Palestinians living in the Israeli-occupied West Bank of the Jordon and the Gaza Strip.

In Aswan yesterday Carter read a statement pledging American backing for the "legitimate rights" of the Palestinians in a way that would enable them "to participate in the determination of their own future."

Although State Department officials in Washington insisted there was no shift policy, American diplomats here said privately that the formulation came within a "hair's breadth" of recognizing the Palestinians' right to "self-determination."

Begin read the statement as encouraging an independent Palestinian state and he warned, "We are not going to stand for such mortal danger to Israel."

Carter's stated postitions on the Palestinian issue have ranged from favoring a Palestinion "entity," then a "homeland" and now his expression of dislike of an independent state and of any apparent role for the Palestine Liberation Organization.

It was a remark by Carter opposing creation of an independent Palestinian state that embarrassed Sadat and prompted the Aswan meeting.

Egyptian officials and editorialists both noted that Carter read his Aswan statement from a prepared text. The newspaper Al Ahram suggested that "perhaps President Carter's lightning visit Aswan resulted in no more" than repairing the damage caused by his earlier remarks in Washington.

All the government-controlled press published a long dispatch today claiming to reveal details of the 45-minute summit conference.

The dispatch said Secretary of State Cyrus R. Vance would stay in Jerusalem "until the declaration of principles of a comprehensive settlement is made." It added: 'This is expected to take three or four meetings. Should the need arise, Vance will shuttle between Cairo and Jerusalem to consult with Sadat over any problem that might crop up."

But both Egyptian and American officials privately said they doubted any such commitment was made in Aswan.

They recognized that Begin needs time to convince his own government coalition and partisans of the necessity of accpeting a declaration of principles for a comprehensive peace.

Egyptian officials expected the talks in Jerusalem to concentrate almost entirely on the Palestinian problem.

Sadat meanwhile has scheduled a full program of officials visits to keep his initiative in the limelight.

In a series of meetings with the relative handful of conservative Arab leaders who have publicly praised him, Sadat flies first to Khartoum Saturday for a one-day visit with Sudanese president Jaafar Nimeri. On Jan. 10 he is to play host to King Hussein of Jordan. So far Hussein has refrained from joining the Egyptian-Israeli talks despite Sadat's increasing tendency to favor linking Jordan with any future Palestinian state.

The shah of Iran, another conservative monarch who favors a Jordanian solution for the West Bank, is due here Jan. 15 and King Hassan of Morocco is expected to arrive three days later.

In other developments in the Middle East:

Lebanese Prime Minister Selim Hoss said his country will reject any peace settlements that leaves Palestinians on its self.

Algerian President Houari Boumediene, on a rare trip abroad, held talks in Saudi Arabia on a mission to rally the Arab to a hawkish policy on peace negiotations.