After a month of the daring innovations and startling firsts of President Anwar Sadat's personal peace campaign, an unmistakable air of letdown settled over Egypt today.

But the Egyptian leader, apparently eager to retain a degree of momentum following the Ismailia summit, held out the hope that he and Israeli Prime Minister Menahem Begin may settle the outstanding issues within two to three months.

As has been his custom in recent weeks, Sadat granted a spate of interviews to foreign journalists. Speaking by telephone with Barbara Walters of ABC News, Sadat asserted that "if we continue to deal like this, in no time we shall be reaching peace.

"Premier Begin yesterday said about three months. I may say two," Sadat said.

When Walters asked him if that meant that he thought that "in two months you will settle the problem," Sadat replied, "I hope so, Barbara."

The Egyptian leader also lashed out bitterly at his Arab critics. In a radio and television talk, he indirectly criticized Syrian President Hafez Assad for joining the "rejectionist front" of radical Arabs opposed to Sadat's initiative.

Sadat asserted that "98 per cent of the Syrian people and the majority of the Syrian armed forces approve my initiative." And he termed as the "worst enemies" of the Palestinian cause those Palestinian groups, including the Palestine Liberation Organization, which took part in the Tripoli, Libya, summit meeting of the "rejectionist" bloc.

There were no signs here today of any backlash against Sadat for the failure of the Ismailia meeting to produce the dramatic breakthrough to peace that this country expected.

Egyptian officials and editorial writers strove to put the weekend events in the best possible light.But there was a definite lull in the cycle of soaring hopes and gloomy fears that have churned the emotions of the Egyptians since Sadat's historic journey to Jerusalem.

Sadat is occupied this week with visiting West German Chancellor Helmut Schmidt. Officials on Sadat's staff said that after Schmidt's official three-day visit, the two leaders are expected to take a brief vacation together in Aswan, in upper Egypt, and afterward Sadat will go to the Sudan. Sadat has passed the negotiating baton to the bilateral ministerial committees on political and military affairs that will begin work in mid January.

In the meantime, Egypt is planning a new public relations campaign to seek international support for Sadat's insistence on a separate Palentinian state on the West Bank of the Jordan. It is difficult to see what more Sadat could do to influence world opinion after a month of almost daily newspaper and television interviews, but it has been announced that Egypt will send "messages and if necessary specials envoys" to other heads of state especially Arab rulers and Western Leaders who have good relations with Israel.

Some observers here think that if the impression spreads that the summit was a failure - a debatable point - it could bring some Arab fence sitters down on the side away from Sadat and give new ammunition to the rejectionists. One objective of the messages Sadat is to send is to prevent the spread of such views.

Egypt is also preparing its own detailed proposals about the future of the West Bank and the Palestinians. In the weekend summit, Sadat rejected the proposal for "self-rule" brought by Begin, but diplomatic sources said the Egyptians were not prepared with specific counterproposals.

Egyptians interviewed today said they felt Sadat had not gotten nearly enough Israeli concessions for the risks he took in going to Jerusalem, and that they expected more from the Ismailia meeting. Several questioned the failure to issue a joint declaration of views that had been promised.

This is a logical consequence of the over-optimistic buildup given to the meeting by the Cairo press, with official encouragement.

Realistic diplomats had warned that a comprehensive settlement probably could not be reached in a few hours of discussions, but hopes for just such a development were high.

The reports from Israel that well-known figures such as Foreign Minister Moshe Dayan were urging a reassessment of Israel's policy on the West Bank led many Egyptians to expect that a quick change was coming.

"The Egyptian Press was at fault," a well-educated pensioner said. "They made it seem that everything was all right and we were on the way to paradise. Now the people are disappointed."

If the press raised hopes too high, some of the blame must be shared by officials of the Foreign Ministry, the Information Ministry and Sadat's staff.

Throughout much of last week they were putting out the word that important and perhaps decisive results were expected from the Ismailia talks. What appears to have happened is that both Egypt and Israel underestimated the other's determination to hold out on points that seem to them vital.

The prevailing view in the government was summed up by an official on Sadat's staff.

"It would be wrong to dwell on the negative aspects," he said. "BUt the fact is the Israelis haven't made the hard choices. We thought they had. They should realize that Sadat could have gone on running this country for many years as the hero of the October war, with the same old slogans. But he didn't. He took the risks because he wants peace, and it's time for world opinion to make Israel understand that."

The Cairo Press said this morning that the real lesson of Ismailia was that Sadat had proved to Israel and to his Arab critics that he would not in fact sell out the Palestinians to get a separate peace with Israel.

"It was neither expected nor was it logical that the Ismailia meeting would achieve the desired peace in one leap . . . Genuine Peace is a hard process requiring courageous and intensive efforts, and the peace which Egypt wants is not based on a separate peace with Israel," said the mass circulation Al Gomhouria. The fact that Sadat and Begin reached points of agreement as well as disagreement, the paper said, is "in itself an important step on the road to peace."

The editor of the most influential paper, Al Ahram. Aly Hamdy Gamal, cited what he said were the achievements of the conference.

In less than one day, he said, Sadat and Begin reached the point that Israel proclaims its respect for Egypt's rightful borders, the two negotiated directly on the real issues, and they agreed that all issues are negotiable. This should show the Arab rejectionists, he said, that Sadat is really making progress.

"The difference over the Palestinian cause is only natural and expected," he said. "No one could have expected Israel would acknowledge a Palestinian state so readily and quickly. The question needs time, patience and an objective outlook."