In a statement that greatly increased the likelihood of a new Camp David summit, President Carter said yesterday he would consider the idea "favorably" if new ministerial-level talks fail to break the deadlock blocking an Egyptian-Israeli peace agreement.

At a news conference, Carter stressed his hope that the ministerial meeting, which is to begin Feb. 21 at Camp David under the leadership of Secretary of State Cyrus R. Vance, will make the breakthroughs necessary to complete the four-month-old negotiations.

But by conceding that he might have to meet again with Egyptian President Anwar Sadat and Israeli Prime Minister Menachem Begin. Carter appeared to be taking reluctant note of the fact that neither country has much faith in the ministerial meeting's chances for success.

Since the breakdown of negotiations in December, both the Egyptians and Israelis have made no secret of their belief that achieving a peace treaty will require another top-level meeting like the one arranged by Carter at Camp David last September.

However, the White House, aware of the catastrophic effects that the failure of a new summit would have on Carter's stature, had been reluctant to take that step. Instead, the administration's strategy has been to have Vance make one more try at cracking the impasse through talks with Egyptian Prime Minister Mustafa Khalil and Israeli Foreign Minister Moshe Dayan.

"I would say that the reality of having a Mideast peace settlement is one of my fondest hopes and dreams and my greatest commitment," Carter said. Noting that the effort has proven harder than expected, he added:

"I think an inevitable next step is to have the foreign ministers of Israel and Egypt come here to meet with Secretary Vance -- I might visit with them briefly -- in an attitude of mutual commitment and flexibility and in a maximum state of isolation...."

He continued: "If that hope is realized, there would be no need for any further summit conference... If that effort is not completely successful and the final peace treaty terms are not concluded, then if there is adequate evidence of flexibility and desire on the part of President Sadat and Prime Minister Begin, then I would certainly consider favorably having them here for a summit meeting."

Despite his careful qualifications, sources familiar with the Middle East negotiations seemed to agree that Egypt and Israel will interpret Carter's remarks as an invitation to consider the meeting with Vance as a preparatory conference for a new summit.

In both countries, the sources noted, there is a strong feeling that only Begin and Sadat have sufficient power and stature to work out their disagreements and that any negotiating effort that lacks their direct participation is doomed to fail.

They pointed out that previous meetings between Vance, Dayan and Khalil have been unsuccessful because the negotiators lacked sufficient authority and flexibility or because they made agreements that later were overruled by their governments.

The main unresolved issue in the talks is Israel's refusal to accept an Egyptian demand that the peace treaty be accompanied by a letter setting out a timetable and target completion date for separate talks on establishing Palestinian autonomy in the Israeli-occupied West Bank and Gaza Strip.

In addition, there are differences involving the draft treaty's provisions for reopening the text of the agreement to future revision and Egypt's reluctance to accept an article stating that the treaty takes precedence over its mutual defense pacts with other Arab states.

However, despite Egyptian and Israeli skepticism about the outlook for the upcoming ministerial meeting, U.S. sources said yesterday the administration is determined to make every effort toward ensuring its success.

The State Department spokesman, Hodding Carter, said planning for the Camp David session under Vance's aegis calls for several days of negotiating. followed by a break to enable the participants to report to their governments and then a return to the negotiating table.