Pope John Paul II used strong and direct language at a mass here today to reaffirm his commitment to strict morality and church doctrines.

He chose to make the firm statement on birth control, priestly celibacy and the sanctity of marriage in a city known as the cradle of Christianity in the Philippines.

It was here that explorer Ferdinand Magellan first landed in 1521 and planted the cross firmly on the ground. Four centuries later, most of the 48 million Filipinos are Catholics.

On the first stop in his three-day swing around rural Philippines, the pope insisted on the celibacy of priests, the sanctity of marriage and spoke out against divorce, artificial birth control and sexual permissiveness.

He told his audience of hundreds of thousands of Filipinos gathered at sunset in unused Lahug Airport that marriage is indissoluble and that the church condemns any attempt to destroy a marriage through divorce or polygamy.

The 60-year-old pontiff said he wanted to reaffirm "as clearly and as strongly as possible what the church of Christ teaches in this respect, and to reiterate vigorously her condemnation of artificial contraception and abortion."

The Philippines has an extensive family planning program that has reduced population growth over the last decade from more than 3 percent to 2.2. percent. The Catholic church in the Philippines has spoken out against birth control, and the family planning program still encounters strong resistance in the countryside.

John Paul also emphasized the value of celibacy and urged priests to be diligent in their pastoral tasks in an address to priests and nuns of the central Philippines upon his arrival.

While the pope supported a conservative position on church dogma, he has expressed liberal views on matters of social justice and human rights since arriving in Manila two days ago.

Today a group of student detainees took the occasion of the pope's visit to Cebu to go on a hunger strike.

The 17 striking students, who were among 21 arrested in May of last year as suspected subversives, wrote a letter to Pope John Paul saying their appeal to President Ferdinand Marcos had been ignored.

The prisoners banged on the bars of their cells in the prison near where the pope was saying mass and authorities put up sand bags to prevent the noise from disrupting the ceremony.

There was no indication that the pope was aware of the protest, but it did distract the crowd trooping to the mass.

More than a million Cebuanos greeted the pope enthusiastically, lining the 11-mile route from the airport where his plane landed to the site of the mass. Many had pitched tents to sleep overnight at the old Lahug Airport where the mass was celebrated.

Organizers of the pope's tour were suprised when First Lady Imelda Marcos turned up with an entourage including Cristina Ford, ex-wife of auto magnate Henry Ford and some European aristocrats.

Church officials had been hoping she would not appear at too many papal functions, fearing that her presence would detract from the pastoral nature of the pope's visit.

The pope leaves Friday for Mindanao where he is to meet with Moslem leaders. The Moslem minority in the south has been waging a secessionist war for eight years following centuries of neglect in a predominantly Christian country.