Secretary of State Cyrus R. Vance said yesterday he is not yet ready to reconvene the deadlocked Middle East talks -- an indication that the United States has not found a formula for resolving the problems impeding an Egyptian-Israeli peace treaty.

Vance was asked at a press conference about expectations for resuming the U.s/.-mediated talks here. He replied:

"We are now discussing the best way of getting the negotiations going again. What we want to be sure of is that in doing this, we do it by a process that will give the negotiations the best chance to be successful."

"Therefore," he added, "we are taking our time in exploring the best way to try and deal with some of the minor problems before we proceed to sit down together and try to thrash out the more difficult issues."

Sources familiar with the talks said his response was an admission of continuing inability to bridge the Egyptian-Istraeli differences that caused the peace negotiations to break down during Vance's Middle East shuttle mission last month.

Since then, both sides have expressed willingness to go back to the bargaining table and have said they will leave it up to Vance to decide the time and place. But, neither Israel nor Egypt has been willing to give ground over the issues that caused the impasse.

According to the sources, that left Vance facing a difficult choice: whether to leave the talks suspended for the time being, despite U.S. fears that this course will erode support for the treaty in both countries, or to restart the negotiations and risk their bogging down again.

His decision to hold off on formal talks was described by one source as "a sign that Vance feels he cannot afford another failure. He obviously does not want to get back into negotiations, at least at his level, until he's more certain that one side or the other will make the necessary concessions."

Although several points in the proposed treaty are under dispute, the biggest differences involve two key issues. One is Israel's insistence that the treaty state explicitly that it takes precedence over Egypt's mutual defense pacts with other Arab states that might come into conflict with the Israelis.

The other stems from Egypt's demand that the treaty be accompanied by a timetable for completing separate negotiations on establishing Palestinian autonomy in the Israeli-occupied West Bank and Gaza Strip. Israel, while saying it is willing to negotiate the autonomy question, has refused to accept a timetable or a target date for completing those talks.

Diring Vance's Middle East visit last month, the United States sided openly with the Egyptian arguments, particularly on the Palestinian linkage issue. That, U.S. officials say was because of Washington's belief that Egypt has to convince other Arab states, especially Saudi Arabia, that it is not abandoning larger Arab interests by making peace with Israel.

More recently, though, Washington has opted for conciliation and quiet diplomacy, seeking formulas tht might enable the two sides to steer around the disputed points. That, the sources said, has been done along the lines sketchd by Vance yesterday.

At present, they said, most contact is being made through the U.S. embassies in Cairo and Tel Aviv under the direction of Alfred L. Atherton Jr., Vance's special envoy for the Middle East. The aim, they added, is to seek legal formulas that will resolve some of the lesser issues and perhaps provide a springboard for tackling the major linkage problem.

If and when that effort proves successful, the sources continues, Vance then will reconvene the negotiations at the foreign-minister level here in Washingotn.

Although U.S. officials privately remain optimistic about a treaty eventually being achieved, they no longer are willing to speculate about how long it will take to wind up the talks that began on Oct. 12.

One clue to the administration's current thinking about the required time span was provided yesterday by President Carter as he received the credentials of the new Israeli ambassador, Ephraim Evron. Carter told the envoy he hoped that they would be observing the treaty "within a very short few weeks..."