Efforts to settle, a festering Moslem rebellion against this country's authoritarian Christian government have suffered a drastic setback because of a Moslem murder of 122 Philippine Army soldiers on nearby Pata Island and a military retaliation to avenge their deaths.

The latest chapter in the bloody conflict has stalemated the efforts of President Ferdinand Marcos' government to end the Libyan-backed secession. According to the president, the conflict has claimed more than 60,000 lives since it broke out in 1972 and has tied down a third of the Philippine Army.

The incidents last month, Moslem leaders here predict, will only intensify their agitation for self-rule. Moslems make up 6 percent of the 48 million predominantly Christian Filipinos. They are the country's largest minority and complain that the Christian majority has long discriminated against their areas.

Independent observers agree that development efforts have failed to transcend cultural suspicions between Moslems and Christians, which have festered through centuries of neglect in the Spanish and American colonial eras. As a result, the southern Philippines remains economically depressed and has the lowest literacy rate in the country.

Marcos' attempts to bring in the Islamic Conference as mediator foundered when Libya's pan-Islamic leader, Col. Muammar Qaddafi, forged with Marcos the 1976 Tripoli agreement. This was to provide limited autonomy for the 13 Moslem provinces in Mindanao Island. But the Middle East-based Moro National Liberation Front, which is spearheading the rebellion with an estimated 22,000 guerrillas, rejected two toothless regional autonomous governments that Marcos set up in 1979 and a cease-fire collapsed.

Moslems and the military are blaming each other for events that led to the Feb. 4 massacre. But the fact that the massacre occurred is not contested. According to the Defense Ministry, a lieutenant colonel lured into a trap and held at gunpoint by the rebels ordered his men to unload their guns. The soldiers were then mowed down and some were beheaded or mutilated before their corpses were burned in what probably was the most bloody incident in the Mindanao secession effort, according to the ministry.

In the Army's strong retaliation, the rebels have so far lost 49 men, including their leader, Cmdr. Meas Unad, according to official count. Ground forces launched large-scale search missions and the Air Force bombarded Pata, the small coral island southwest of Mindanao where the massacre occurred, in the far-flung Sulu Archipelago 95 miles southwest of here.

The bombing ceased early this month and ground fighting also is winding down, according to the Southern Command, the military arm in Mindanao.

But the fighting on Pata Island, by all accounts, already could turn out to have been as destructive as earlier rounds on other islands, particularly to civilians. Nearly 7,000 civilians, half Pata's population, were caught in the crossfire and have been evacuated to safe centers on the island. Against a background of food shortages, the first cases of malaria and stomach ailments have been reported by officials of the regional autonomous government.

The full death toll from bombing and strafing by the Air Force could not be determined. The government keeps a tight lid on all information from the area. But the Southern Command chief, Brig. Gen. Delfin Castro, was quoted as saying it is inevitable that many civilians get killed in an operation of Pata's scale.

The island has been blockaded and all boats and fishing vessels were either destroyed or seized, Southern Command officials said.

A ranking leader of the Tausugs, the warlike Moslem tribe of the Sulu group, who recently visited the Pata evacuees said: "There was fear and anger in their eyes. The indiscriminate shooting has hardened the feelings of the Tausugs."

"It has made it difficult for us to persuade the people to vote yes in the April 7 plebiscite," he continued, referring to a referendum in which Marcos seeks to amend the constitution so he can run for president again next June.

This leader, who asked not to be identified, said he considered the retaliation operations unwise because within days of the massacre, the estimated 300 rebels on Pata had escaped in five speedboats in the direction of the Malaysian state of Sabah, where the rebels often normally seek sanctuary.

Another Moslem leader, Sharif Zain Jali, a teacher of Islamic law, has gone to mosques in Zamboanga City to agitate the Moslems to "sharpen their bolos," according to a top government official referring to local curved knives.

In an interview, the Cairo-educated Jali declared: "We are no longer safe. I Told everybody in the mosques to be prepared to defend themselves. I told them not to surrender their arms."

Another Sulu leaders, Kalbi Tupay, a former rebel commander and now a member of parliament urged the president to pull troops out of Pata because, he said, their presence is provocative.

Part of the issue now is a feeling by many Moslems that government-appointed Moslem leaders have chosen not to probe too deeply into grievances.

The autonomous government of western Mindanao, for example, sent a fact-finding team to Pata who weeks ago to investigate charges of military abuses as the reasons for the anger leading to the massacre. The leader of the team and speaker of the local assembly, Nur Ututalum, on his return vehemently denied the allegations, saying the evacuees told him there were no abuses by soldiers before the massacre.

Jali, who claimed many of his relatives in Pata have been killed, said bitterly: "They couldn't tell the truth because of the Army."