Israeli Foreign Minister Moshe Dayan said yesterday the purpose of next week's Middle East peace negotiations in Washington will be to reach a separate treaty with Egypt, and that the outcome is not dependent on Progress on the West Bank and Gaza Strip autonomy issue.

"We are going to negotiate a peace treaty between Egypt and Israel, and that is the main issue," Dayan said upon leaving here for New York, where he will address the U.N. General Assembly on Monday. He will meet today with secretary of State Cyrus Vance and return to Washington for the peace talks scheduled for Thursday.

There has been some apprehension here that the Egyptian delegation might attempt to link the Sinai Peninsula issue with the future of the West Bank and Gaza, thereby jeopardizing the conclusion of a separate peace treaty within three months, as called for in the Camp David summit agreements.

Dayan, in an airport news conference, sought to dispel that notion, saying there are "two mains elements" to be discussed in Washington: the "nature of peace" between Israel and Egypt, meaning the normalization of relations, and the details of the military agreements the Camp David summit, including the withdrawal of Israeli forces from the Sinai.

A Foreign Ministry spokesman later repeated Israel's understanding of the "bilateral" nature of the Washington talks, saying. "It is his (Dayan's) understanding there is no connection between the progress of the bilateral talks with Egypt and progress on negotiations over (the West Bank) and Gaza strip."

Some senior government officials have been quoted as saying the Israeli delegation is prepared to take up the West Bank autonomy issue in Washington, because they assume the Egyptians will for ask parallel talks on the Sinai and West Bank issues.

Israeli correspondents in Cario report that they are being told by Egyptian officials that there is a linkage between the two issues, and that Egypt hopes that even if Jordan does not join the peace process, Israel will take some unilateral steps to implement Palestinian autonomy.

Acting Foreign Minister Boutros Ghai was quoted in Maariv, the afternoon newspaper, as saying, "Egypt believes in the necessity to have a minimum co-ordination between the agreement on the Sinai and the steps in the West Bank."

However, U.S. officials have said that the Washington talks will focus only on the Sinai, and that talks on establishing autonomy in the other occupied territories will begin only when Palestinians come forward to participate the discussions.

Dayan said a difference of interpretation still exists between Israel and the United States over how long Prime Minister Menachem Begin agreed to freeze settlements on the West Bank.

Begin regards the commitment as lasting more than the three months allocated to talks on an Israeli-Egyptian treaty, while President Carter maintains that the pledge was for up to five years set aside for West Bank-Gaza negotiations.

Dayan said the crisis in Lebanon, where the Syrian troops are battling Israeli-supported Christian militias, should not jeopardize the peace talks.

In response to a question, he said, "I don't really think it should effect in any way the negotiations, and we haven't received any indication from Egypt that what is happening in Lebanon has to go too with the negotiations."

He complained, however, that Syria was acting in a "very negative" fashion, and suggested that its motive may be to disrupt the Camp David agreements and conquer Lebanon at the same time.

There was a growing sense of urgency in Israel's Cabinet last night over the Lebanon situation. Begin was said to be receiving reports on the Beirut fighting every two hours, and Israel was reported to have warned Syria through U.S. diplomatic channels that it would not stand by idly while the Christian inilitias are devastated.