PLO leaders drafted a historic declaration Monday to be presented to the group's parliament-in-exile that implicitly recognizes Israel's right to exist.

Several conference sources said they expected up to 85 percent of the 450 members of the Palestine National Council to endorse the document.The council's political committee met behind closed doors to debate the wording of another part of the declaration, a commitment distancing the Palestine Liberation Organization from terrorism, conference sources said.

The sources, who are on the drafting committee, said they did not expect any differences over the draft but would not elaborate.

The declaration sets out a new political strategy by endorsing U.N. Security Council Resolution 242 - which recognizes Israel's right to exist - thus satisfying one of Washington's key conditions for dealing with the PLO. The resolution also calls for Israel's withdrawal from territories occupied in the 1967 Middle East war.

In Washington, President Reagan said Monday that if the council does accept Resolution 242, "that would be some progress." But he said there are other problems that remain to be solved before a breakthrough in the Arab stance toward Israel would be achieved. He did not elaborate.

On Tuesday, the council is expected to end its extraordinary four-day meeting with a declaration of independence for the West Bank and Gaza Strip, where Palestinians have been revolting for 11 months against Israel's 21-year occupation.

In a radio interview Monday, PLO chief Yasser Arafat called the council meeting a "turning point in the course of the Palestinian struggle that will also influence events and developments in the Arab world."

He praised the council for what he called its "democratic spirit" and criticized opponents of the latest Palestinian moves toward peace without mentioning any specific names or groups as "swimmers against the current of history." The Radio Monte Carlo interview was monitored in Nicosia, Cyprus. In closed-door committee meetings, there had been strong opposition to Resolution 242 from the PLO's Marxist-oriented groups, particularly George Habash's Popular Front for the Liberation of Palestine.

But Habash's faction, the second-largest of the eight groups comprising the PLO, agreed Sunday to go "with the rule of the majority," a spokesman said.

Arafat had hoped for a consensus on Resolution 242 to avert further splits within his guerrilla movement and in the national council, which first assembled in 1964.

Arafat is hoping political moderation coupled with increasing sympathy for the Palestinian cause brought on by the Palestinian uprising will eventually lead to an international peace conference on the Arab-Israeli conflict.

The conflict in the occupied territories has left at least 311 Palestinians and 11 Israelis dead since it began Dec. 8.