Druse warlord Walid Jumblatt resigned his post as minister-without-portfolio on Friday, dealing a blow to the half-Muslim, half-Christian government formed to steer Lebanon out of civil war.

The sudden resignation means the 30-seat Cabinet now lacks two of the three major militia leaders Prime Minister Omar Karami had sought to attract to the national reconciliation government he formed on Dec. 24.Christian chieftain Samir Geagea, who heads the Lebanese Forces, a rightist militia, has refused to take up his post as minister-without-portfolio.

Christian leaders have charged that the new government tilts overwhelmingly toward Syria, the main power broker in Lebanon with 40,000 troops deployed there under a 1976 peacekeeping mandate from the Arab League.

Nabih Berri, leader of the mainstream Shiite Muslim Amal militia, was also named minister-without-portfolio in the government.

The government, formed under an Arab League-brokered peace plan, is to disband the various militias and try to spread state authority over the whole of war-shattered Lebanon.

It received an overwhelming vote of confidence in parliament on Wednesday to end the nearly 16-year civil war, which has claimed more than 150,000 lives.

The government also plans to achieve equality between Muslims and Christians in parliament by filling vacancies and increasing the number of seats from 99 seats to 108. The present parliament was elected to a four-year term in 1972; because of the civil war there have not been elections since.

Jumblatt, 43, announced his resignation at the inauguration of a public library in the town of Baaqlin in his Chouf Mountains power base southeast of Beirut.

"I announce my resignation from the government . . . For personal reasons I shall stay away from the political arena for the time being," Jumblatt said, without elaborating.

He also said he would "resist moves" by the government to appoint a parliamentary replacement for his late father, who was gunned down by unidentified assailants in March 1977. "Kamal Jumblatt's seat cannot be filled by appointment," the younger Jumblatt warned.

Geagea also said he opposed the government's appointment of new parliament members. "We shall resist, at any cost . . . Representatives of the people should be elected, not appointed," Geagea said in a TV interview on Thursday.

He said he would continue to refuse to serve in the new government. "I wonder who is going to reconcile with whom? We're not going to take part in this government, and I'm sure the leaders of other major militias are not satisfied with this government," Geagea said.

In addition to Geagea, Phalangist leader George Saadeh, also a Maronite Christian, has refused to take up his post as minister of telecommunications in Karami's government.