Israeli planes hit Lebanon again

Israeli planes launched their most extensive raids in Lebanon in a month Monday, hitting Syrian, Palestinian, and Lebanese-leftist targets in central Lebanon, security sources said.

The Beirut sources said the raids were concentrated in an area where the main Beirut-Damascus highway enters the Bekaa Valley. They said there had been casualties, but no details were given.

Security sources said the Israelis bombed Syrian positions near the town of Zahle in the Bekaa, Palestinian positions on the Damascus highway just inside the Bekaa, and Lebanese-leftist militia posts nearby.

The raids came after the Israeli high command issued a detailed statement accusing the Syrians and Palestinian guerrillas operating from behind Syrian lines of repeatedly violating a ceasefire in the Bekaa.

Meanwhile, Lebanese Army units edged into leftist-held parts of west Beirut after heavy clashes Sunday with militiamen resisting their advance in the first test of the government's effort to impose law and order on Muslim west Beirut. The regular troops stationed their armor along the ''green line'' dividing the city and took over the local headquarters of the pro-Palestinian ''Partisans of the Revolution'' group.

The White House Monday urged all parties in the Lebanon conflict to prevent a recurrence of the fierce fighting that broke out Sunday in Beirut, saying it had not ruled out sending in United States Marines again.

In a separate development, the seven-member Arab mission scheduled to visit the US for talks on the Arab-Israeli conflict will hold its first meeting in Tunis Sept. 21. Palestine Liberation Organization leader Yasser Arafat reportedly set the meeting date.

Also decided at Fez and disclosed Monday: moderate Arab leaders are to sound out Egyptian, ostracized by the Arab world for making peace with Israel in 1979, on its willingness to rejoin Arab ranks.