Secretary of State Cyrus Vance tonight concluded his talks with President Anwar Sadat on ways to resolve the issues blocking an Egyptian-Israeli peace treaty and prepared to go to Israel with what U.S. officials called "new ideas" to discuss with Prime Minister Menachem Begin.

"I'd say it was a positive and helpful set of meetings," Vance said of the three sessions he has had with Sadat since Sunday. "We made good progress."

He refused to discuss the substance of his talks with Sadat, but U.S. sources made clear that the two had settled on ideas, that Egypt finds acceptable for dealing with the two key problems that have deadlocked the U.S. mediated peace negotiations for a month.

Now, Vance faces the second phase of his Middle East mission-trying these ideas out on the Begin government when he goes to Israel Wednesday. That the negotiating process is still far from finished was underscored by Sadat, who said at the conclusion of tonight's meeting that the expects Vance to return here after talks with the Israelis.

Reporters asked Sadat when that would be. The Egyptian leader shrugged, pointed at Vance and said: "He has to decide that."

U.S. officials in Vance's party underscored once again that President Carter considers it very important to reach agreement on the treaty by Sunday-the Dec. 17 deadline specified at the Camp David summit meeting for concluding the negotations.

But the officials also said they had no way of predicting how long Vance will be in Israel and whether the drive for completion will involve him in a Cairo-Jerusalem shuttle stretching beyond Sunday.

(In his press conference Tuesday in Washington, President Carter said: "I consider the deadline date to be quite important. If the Egyptains and the Israelis cannot keep a commitment on a three-month conclusion of the peace treaty when they themselves are the only two nations involved... then I think it will be very difficult for them to expect the terms of the treaty they are negotiating to be carried out with assurance." Carter also said he considered the differences between the two sides to be minor.)

Earlier today. Vance completed a round trip between the two capitals, returning here after an overnight trip to Jerusalem for the funeral of former Israeli prime minister Golda Meir.

Although he talked briefly there with Foreign Minister Moshe Dayan and Defense Minister Ezer Weizman, the serious bargaining on the Israeli side of the dispute will not start until he sits down tomorrow for the first of his meetings with Begin.

One of the two big issues to be thrashed out involves Sadat's insistence that the treaty be accompanied by a letter setting out a timetable for separate negotiations on establishing Palestinian autonomy in the Israeli-occupied West Bank and Gaza Strip areas. So far, Begin's government, while agreeing to negotiate on Palestinian self-rule, has refused to accept a timetable.

The other principal problem concerns Egypt's desire to change an article in the text of a draft treaty already accepted by Israel. The disputed article states that the document takes prcedence over the two countries' other treaty obligations-a condition that would appear to prevent Egypt from assisting other Arab states that might come into conflict with Israel.

In the discussions here, Vance is known to have presented Sadat with some U.S. ideas for getting around these two problems, and sources close to the negotiations hinted tonight that the proposals tentatively agreed to by Sadat follow the contours of the American suggestions.

Essentially, the U.S. strategy was to convince Sadat that he should not seek to change the text of the treaty draft accepted by Israel. Instead, the United States has argued that Egypt's concerns can be covered adequately by mutually agreed upon exchanges of letters and interpretative notes accompanying the treaty.

Under U.S. proposals, the timetable for negotiating Palestinian autonomy would be covered by such a side letter. To make the idea acceptable to the Israelis, Vance reportedly has argued to Sadat that the timetable should be labeled as a target that the two sides hope to meet rather than a fixed deadline that must be accomplished within the specified time limits.

In regard to the article about the treaty's precedence, the United States is known to feel that the language in the draft treaty protects Egypt's positon from a legal point of view and that Sadat's concern is really political-namely his fear of being accused of abandoning the interests of the Arab world to make a separate peace with Israel.

On this point too, Vance is believed to have convinced Sadat to give up on changing the language of the article and settle instead for another side letter eleborating and clarifying Egypt's legal obligations toward its other treaty arrangements.

What was unknown tonight was the precise nature of what these proposed side letters will say on the two issues and whether the ideas accepted by Sadat also will also be acceptable to the Israelis.