A political split widens between Muslims and Christians in Lebanon

Tension between Christian and Muslim political rivals in Lebanon is again heating up, accentuating flashpoints for future internal strife. Three developments over the past week have heightened apprehension about the already frail hopes for restoring peace and stability if foreign armies pull out.

* Political polarization.

On Tuesday, the Lebanese Parliament formally ratified the United States-designed accord with Israel on withdrawal of foreign forces. It was a move aimed at showing unity, but instead brought out the differences between rightist and leftist groups in the Arab world's only democracy.

Although the pact received the endorsement of 65 of the possible 91 votes after two days of heated debate, 19 members of Parliament did not even show up for the crucial session. Twelve - including a former prime minister - had openly declared they were boycotting the debate.

Another former prime minister abstained. (The post of prime minister in Lebanon has traditionally been delegated to a Sunni Muslim.)

Leftist, predominantly Muslim, opponents have become gradually more outspoken in their criticism of the controversial agreement with Israel negotiated by the Christian-dominated government of President Amin Gemayel.

They have argued that the Arab world would not support Lebanon if even a small Israeli military presence was permitted. It has not gone without notice that no major Arab state has yet backed the accord.

They also said the timing for ratification was bad, since the pact with Israel represents only one-half of the peace process. Their fears the move might trigger further Syrian wrath appear to be justified, for Syria's state-controlled press Wednesday called for attacks on the Israelis to be expanded to include Lebanese who endorsed the accord.

* Broken cease-fires.

The political polarization among factions was matched by a renewed round of fighting between Christian and Druze Muslim militias in the Shouf mountains overlooking Beirut. They followed the usual pattern of exchange of light weapons fire escalating to artillery and rocket duels. Both charged the other side was responsible.

Repeated cease-fires over the past six months after similar clashes, in which more than 200 have been killed, have all collapsed. Indeed, one Druze soldier recently interviewed said he hoped the Israelis, who occupy the Shouf mountains, would withdraw soon so there would be no restrictions on ''settling scores.''

* Druze claims of uneven balance of power.

Druze leader Walid Jumblatt, who is also Lebanon's leading leftist, disclosed last Friday that he had rejected all behind-the-scenes approaches to restore calm.

He said there would be no new ''understanding, not even in a thousand years, '' unless major changes were instituted by the government as part of a national entente. The various Muslim sects have long been demanding reforms that would even the balance of power, now dominated by the numerically weaker Christians.

Mr. Jumblatt's wide-ranging interview offered a third major setback to the government. He also announced he was not returning to Beirut and would instead set up headquarters in Syria, Jordan, and France.

Mr. Jumblatt recently helped to form a new movement to oppose the Gemayel regime, a group that includes a former president, a former prime minister, and several leading leftists. His announcement triggered new fears that the movement may attempt to establish an alternative government in Lebanon.

Mr. Jumblatt charged that Mr. Gemayel has protected Lebanon's Christians, including the technically illegal Christian ''Lebanese Forces'' militia, while persecuting Druze, Sunni, and Shiite Muslims.

He claimed that the government would not tolerate criticism of its policies and often arrested those who did. Diplomats confirm that hundreds of predominantly Muslim men have been detained by the government for as long as nine months.