Israel and Egypt today completed their third round of negotiations on autonomy for the West Bank and Gaza Strip Palestinians without agreeing on an agenda or a declaration of principles.

As both sides appeared to be marking time in anticipation of next month's summit meeting in Alexandria between Israeli Prime Minister Menachem Begin and Egyptian President Anwar Sadat, the negotiators announced a leisurely schedule of bargaining sessions that left little likelihood of substantive progress this summer.

The next session after the meeting July 5 in Alexandria will be held Aug. 5 in this Mediterranean resort town, followed by a meeting on Aug. 20 in Alexandria.

In the meantime, technical committees will meet periodically, but the tone of today's statements by the heads of delegations suggested that both sides were leaning on Sadat and Begin to give some impetus to the talks.

The Egyptians, in particular, showed no signs of anxiety over the place of the talks, giving rise to speculation among some Israelis that there would be no sign of urgency until Israel withdraws its forces and civilian outposts from the Sinai peninsula in the first phase of implementation of the peace treaty.

Israeli negotiators said the bargaining teams came close to agreeing on an agenda and probably could have released one by extending today's session. However, the sources said, neither side was dismayed at putting the decision off until the next round of talks.

In a bland, seven-paragraph joint statement, the delegations said Egypt had introduced "objectives on the process and the future work," while Israel suggested "practical ways and means to advance the negotiations."

Egyptian Prime Minister Mustafa Khalil said he was hopeful that the participation of U.S. envoy Robert Strauss, who will head the American delegation at coming sessions, would provide some momentum to the talks.

"From experience, we know that the negotiations succeed when the United States is a full partner," Khalil said.