President Corazon Aquino is trying to make peace with Moslem insurgents in the Philippines' southern islands but is hitting a familiar and serious snag -- how to sort out who actually speaks for their highly factionalized Moro National Liberation Front.

The Moslem insurgency, which is separate from one being mounted by the Communist New People's Army, is largely dormant today. Still, with large stocks of weapons remaining in Moslem hands, the government wants to negotiate the rebels' eventual surrender and disarming.

Moslem leaders say that Aquino's government, like past ones, has only token Moslem representation at the top. They say it must act quickly to open negotiations and prove good faith in tending to their demands for greater control of local affairs.

"If the issue is prolonged," Abul Khayr Alonto, secretary general of the Moslem Federal Party, said in an interview, "it might require another war to remind this government of its commitments to the Philippine Moslem people."

The Aquino government and diplomatic observers have tended to treat such warnings as little more than rhetoric. But attacks by Moslem guerrillas have continued sporadically. In one incident, an MNLF group ambushed and killed a municipal council member last week near Jolo in the Sulu archipelago, a military report said.

In March, a Moslem delegation claiming a mandate to negotiate arrived in Manila from exile. Traveling to Mindanao island, the southernmost main island of the Philippines, the group signed what were called preliminary cease-fires with local Army commanders.

The delegation was received by senior government officials, including Vice President Salvador Laurel, but denied access to Aquino, apparently because the government had concluded that it represented only a minor faction in the MNLF and giving it too many honors would jeopardize contacts with the larger groups. The cease-fire accord was played down in Manila on the grounds that in many places, unofficial truces were already long in place.

"It is difficult to be talking to separate groups," Aquino told a recent news conference. "I would much rather that we talk to the leaders who will be able to speak for the entire Moslem group."

But Moslems have claimed this is merely an excuse for inaction. Just before the delegation left town, its leader, Sultan Macapanton Abbas Jr., said that "if there is any obstacle to peace, it is always the president."

Moslems make up about 5 percent of the Philippines' 55 million people. Marxist ideology plays virtually no role in their fight, which is a continuation of a centuries-old struggle against control by Christian-dominated governments in Manila.

Full-scale rebellion exploded after former president Ferdinand Marcos declared martial law in 1972. Tens of thousands of people died. Fighting was so fierce that in one battle almost the entire town of Jolo was leveled.

Peace was largely restored after a 1976 agreement signed in Tripoli, Libya, between the MNLF and the Marcos government in which Marcos agreed to grant a measure of autonomy. Today, the Moslems are considered only a minor threat compared to that of the unified New People's Army, and are clearly getting less attention from the government.

By most accounts, the MNLF is now composed of three major factions, though some analysts see four. They tend to break down along tribal lines. The groups have received aid from a variety of Islamic countries, including Malaysia, Saudi Arabia and Libya.

Abbas' group and another group led by Hashim Salamat advocate autonomy for the south and say the basis for new talks should be the Tripoli agreement, which Marcos is accused of having failed to keep.

But a third faction, led by one of the movement's original father figures, Nur Misuari, is said to want total independence for the south. People claiming to be Misuari's emissaries have condemned Abbas' trip here and warned against treating his group as the MNLF leadership.

Aquino continues to keep feelers out. Her brother-in-law, Agapito Aquino, attended a large conference of Moslem leaders in Zamboanga town on Mindanao in April and in a 45-minute speech asked for understanding and more time.

Aquino has indicated willingness to discuss autonomy but not a secession. When yet another Mindanao group, headed by a former supporter of Marcos named Reuben Canoy, said it was going to declare a "Federal Republic of Mindanao," the government said it would arrest anyone taking part on charges of sedition.

The group backed off, holding a meeting of about 500 people on April 25 in Cagayan de Oro city but stopping short of signing an outright independence declaration.