Israeli warplanes bombed northern Lebanon today, attacking Palestinian sites on the outskirts of Tripoli and ending a precarious 11-day cease-fire arranged by the United Nations.

The jet fighters attacked in the Nahar Bared area, a stronghold of George Habash's Popular Front for the Liberation of Palestine about 40 miles north of Beirut.

Israeli military officials said the target areas were used for organizing and training terrorist squads and that intelligence had disclosed plans to launch attacks in Israel from the bases.

A Palestine Liberation Organization spokesman in Beirut said the warplanes hit the Nahar Bared refugee camp, killing three persons and wounding several others. About 20,000 Palestinians and Lebanese live in the center.

It was the same area Israeli gunboats bombarded April 22 following the Palestinian terrorist attack on the northern Israeli town of Nahariya in which four civilians died. Lebansese provincial authorities placed the death toll in those retaliatory strikes at about 60.

Today's attack appeared to end a tenuous cease-fire worked out by the U.N. peacekeeping force in Lebanon on April 26 following the heaviest fighting since Israel's invasion of southern Lebanon 13 months ago.

Since the cease-fire, Israel restricted its sorties to supersonic flights over Palestinian areas, which prompted Syria to send its Mig21 fighters over Beirut. There were no clashes.

A U.N. spokesman herern Lebanon area where fighting prompted the agreement., and that, technically, the air strike may not be covered by the agreement because it occurred far from the southern Lebanon area where fighting promoted the agreement.

However, anticipating the pattern in which Israeli attacks in Lebanon are followed by Palestinian shelling of civilian settlements in northern Galilee, northern Israel was placed on alert following today's raid.

An Israeli military spokesman denied that the air strike represented a breech of the agreement, and said it was in keeping with Israel's policy to "hit any time and any place" to preempt terrorist attacks inside Israel.

"First of all, we didn't sign any cease-fire with the terrorist, and whatever agreement there was concerned the south" of Lebanon, the spokesman said.

Because Israel has refused to deal directly with the Palestinian organizations, U.N. officials negotiated the cease-fire by approaching Israel and the Palestinian leadership separately. That arrangement, Israeli military officials stressed today, was not intended to except Palestinian organizations from strikes launched in anticipation of terrorist actions.

The Army disclosed no details of the purported terrorist plans.

Palestinian forces crossed south of the Litani River last night and attacked Israel-backed Lebanese Christian militia strongholds at Marjayoun, Israeli officials said today.

They said the force was driven back by a Christian militia mechanized patrol, and that the Palestinians and Christians exchanged artillery fire for several hours afterward.

Meanwhile, Israel's Cabinet, responding to Egyptian suggestion of an Islamic summit on the future of Jerusalem, today issued a statement reiterating that the "eternal capital" will never be divided.

"The government of Israel declares and reiterates that Jerusalem is the eternal, united and indivisible capital of the state of Israel. Unlike the period of Jordanian occupation, there has existed in Jerusalem ever since June 8, 1967, total freedom of access for Jews, Christians and Moslems to their respective holy places. That shall always be," the Cabinet declared. Israel captured East Jerusalem from Jordan during the 1967 six day war. CAPTION: Map no caption, By Dave Cook-The Washington Post