Palestinian guerrillas in southern Lebanon fired artillery shells into the Israeli-supported Christian enclave along the border today, Israeli military sources said. It was the fourth day that the cease-fire called last Friday had been broken, but no damage or casualties were reported.

Military sources said the shellings were cursory compared with guerrila barrages on Friday and Saturday.

The Israeli Army command said that neither Israeli artillery units nor those of Christian militia commander Maj. Saad Haddad fired in response to today's shelling.

The shellings followed an announcement in Beirut by the Palestine Liberation Organization that all PLO factions, including the radical Popular Front for the Liberation of Palestine-General Command, would honor the cease-fire. Christain militias reportedly have fired one artillery around toward the source of one of the attacks, about 3:45 a.m. yesterday.

Israeli officials said that despite the minor infractions, the cease-fire is generally holding and that the PLO appears to be making an attempt to discipline the popular front.

Deputy Defense Minister Mordechai Zippori, during a tour of northern Israel, said today that if Palestinian guerrilla attacks continue, however, Israel will be forced to retaliate by means that may be more severe than previous reprisals.

"Let us say, for us it is a chance to demonstrate to a free and democratic world who are the people responsible for this shooting that is going around. . . . Now, everyone around the world knows exactly from which side the fire is coming," Zippori said.

He added, "For us, it is important because we have some political limitations to our decisions how to react and how to deal with this situation. After this thing has been demonstrated, and if the fire will not be stopped very soon, and it doesn't matter if it is on Haddad's people or on our people in Israel, we shall deal with it and find solutions."

Meanwhile, the Knesset (parliament) today formally approved by an overwhelming majority the agreement reached by Israel, the United States and Egypt for the creation of a multinational peacekeeping force to be deployed in the Sinai Peninsula when Israel withdraws from the last third of the occupied territory next April.

The only political parties to oppose the agreement with the Communist-dominated Democratic Front for Peace and Equality and the Tehyia (renaissance) Party, with three members, which opposed the Camp David peace treaty.

Wire services reported the following from Beirut:

Israeli Air Force planes flew reconnaisance missions over southern Lebanon, Beirut and the northern port of Tripoli today. The planes drew antiaircraft fire from Palestinaina gunners over Tripoli and when they buzzed the Palestinian refugee camp of Sabra on Beirut's outskirts, an area that was one of the targets of the Israeli raids July 17 that killed 300 people.

Syria' state-run Damascus Radio accused Israel of violating the Lebanese cease-fire agreement with the flights and warned it will attempt to shoot down future flights.

The Popular Front for the Liberation of Palestine-General Command, the PLO faction that initially rejected the truce, denied Israeli reports that its guerrillas fired shells into the Christian enclave in southern Lebanon.

Meanwhile, about 200 Palestinians and Lebanese demonstrated in front of the American Embassy in Beirut to protest U.S. support of Israel. The 20-minute, peaceful protest was organized by the Democratic Front for the Liberation of Palestine, a PLO faction.