An article yesterday incorrectoly said that under the War Powers Act U.S. forces must be removed from hostile situations within 120 days unless there is a declaration of war or congressional approval. The correct time limit is 60 days after a formal notification to Congress, with a 30-day extension permitted under presidential certification.

President Reagan said yesterday that he has approved conditionally the dispatch of American military forces to help evacuate trapped Palestinian guerrillas from Beirut and assist the Lebanese government in establishing order there.

The president's statement to a group of state and local officials in Los Angeles followed the leak to the Israeli press in Israel of the plan, which was approved secretly by Reagan Friday night. After the unexpected revelation early yesterday, senior White House and State Department officials began calling members of Congress to give them the news.

Lawmakers were told that France is expected to join 800 to 1,000 U.S. Marines in an evacuation and peace-keeping force, and that the Palestine Liberation Organization fighters probably will go to Iraq, Syria and Algeria.

While U.S. Navy craft probably will be involved, Pentagon sources said that major transport of the Palestinians is likely to be via chartered ships under the flag of the International Red Cross, with the U.S. fleet providing ferrying and escort services.

The initial congressional reaction was mixed. Some lawmakers endorsed the outlines of the administration-described plan, but others spoke of the dangers of U.S. casualties and of a prolonged involvement in Lebanon.

House Foreign Affairs Committee Chairman Clement J. Zablocki (D-Wis.), who expressed "serious reservations," said he will convene his committee at the earliest possible moment for a detailed administration briefing.

Reagan was reported late yesterday to be telephoning some key members of Congress to smooth the way for the proposal.

Deputy press secretary Larry Speakes said the White House intends to comply to the fullest extent with the provisions of the War Powers Act, which requires a formal report to Congress within 48 hours when U.S. forces are introduced into a hostile environment. Under the law, the forces must be withdrawn within 120 days in the absence of a declaration of war or special congressional approval.

Speakes said any U.S. military involvement would be limited to a "comparatively brief" duration, which an official estimated to be no more than 30 days.

U.S. forces will become involved, Speakes added, only if there are assurances of their safety and if all parties agree to their participation as part of a package deal to end the PLO military role in and around Beirut.

A senior administration official said, in addition, that there were four explicit conditions to the president's approval: that there be a formal request from Lebanon, that another country participate, that the role be limited by geography and that there be a time limit.

A State Department official expressed the belief that France would provide a force roughly equal to that of the United States. But this could not be confirmed last night.

"The specific mission of such an international peace-keeping force, if agreed to, would be to assist Lebanese armed forces in the orderly and safe departure from Beirut of armed PLO personnel and to assist in the transition of authority to the Lebanese government in Beirut," Speakes said.

He quoted Reagan: "If a brief, limited involvement of U.S. personnel is what it takes, I believe we must do it."

U.S. special envoy Philip C. Habib, who in negotiations between the PLO and the Lebanese government is seeking to arrange a PLO withdrawal, recommended the American military role. According to Reagan, Habib reported the view of the Lebanese government last weekend that a multinational "temporary peace-keeping" force in Beirut "might be essential" to success in the negotiations.

Washington Post staff writer Herbert H. Denton quoted a White House official in Los Angeles as saying that U.S. participation was "a bargaining chip" requested by Habib and that Reagan had approved it conditionally if it would mean breaking an impasse.

Washington sources said intense discussion among policy makers of a possible role for U.S. forces in resolving the Beirut situation went back at least to the middle of last week. After Reagan approved the plan at 9 p.m. Friday, detailed planning was done all day in Washington Saturday under supervision of the National Security Council.

Israeli Prime Minister Menachem Begin was informed of the proposal late Saturday by U.S. Ambassador to Israel Samuel Lewis in a meeting timed to precede Sunday morning's important meeting of the Israeli cabinet, according to official sources.

In his remarks yesterday to officials of 13 western states, Reagan emphasized the continuing delicate nature of the negotiations. Despite the U.S. agreement to participate in the peace-keeping role, officials cautioned that it is far from certain that a negotiated settlement can be concluded and implemented to the satisfaction of Israel, Lebanon and the PLO.

The deployment to Beirut would introduce U.S. forces into a hostile situation in the Middle East for the first time in the Reagan adminstration, and would be one of the few times U.S. forces have been so deployed since the Vietnam war.

Defense sources said U.S. commanders in the Mediterranean had been notified last weekend of the possibility that American forces might have a Beirut role. A helicopter carrier and four other amphibious ships carrying about 1,800 men of the Marine Amphibious Ready Group have been moved to a standby position near Lebanon's coast, sources said.

Three of the ships were dispatched on short notice Sunday from the Italian port of Taranto to join other U.S. ships in the eastern Mediterranean, according to the sources. The U.S. task force in the area includes two aircraft carriers, the Forrestal and the Independence.

Among congressional leaders, a note of caution was sounded by Senate Majority Leader Howard H. Baker Jr. (R-Tenn.), who said he wanted detailed discussions with administration officials before making a judgment. "I have previously expressed my opposition to the use of American troops in Lebanon, and I've expressed that directly to the president," Baker said.

Sen. Charles H. Percy (R-Ill.), chairman of the Senate Foreign Relations Committee, said the plan "would be considered if this is the only way" to get the PLO out of Beirut and avoid further bloodshed. He made safeguards about the nature and duration of a U.S. involvement conditions of his approval, but these were similar to the assurances the White House announced.

Senate Minority Leader Robert C. Byrd (D-W.Va.) and the Democratic whip, Alan Cranston (D-Calif.), also cautiously supported the plan.

Sen. Charles McC. Mathias Jr. (R-Md.) warned that various potential dangers should be weighed carefully by the administration and Congress before a commitment is made.

He also said the United States should use the opportunity to seek new understandings with Israel about restraints on the future use of U.S.-supplied weapons and greater Israeli flexibility on negotiations to give autonomy to the Palestinians in Israeli-occupied territories.