An American missionary and 10 Roman Catholic Filipino nuns were kidnaped over the weekend in southern Mindanao by armed men believed to be Moslem insurgents, military authorities reported here today.

The abduction of Brian Lawrence, 30, of Madison, Wis., is the first involving an American in more than three years in either of the Philippines' insurgencies -- the one involving Moslems in the south and the other involving communists in several regions of the island nation.

In Washington, the State Department said it was aware of the report but was unable to confirm its accuracy. Family members in Wisconsin said that the organization with which Lawrence is affiliated, International Missions Inc. in Wayne, N.J., had informed them of the kidnaping, United Press International reported.

No group asserted responsibility for the kidnapings, and well-informed observers here cautioned that the abductions could have been nonpolitical acts of banditry by former Moslem guerrillas who, unable to find employment after surrendering to the government, have resorted to such actions.

Brig. Gen. Pedro Balbanero, deputy chief of the Army's Southern Command, said he suspected that the armed abductors were Moslem terrorists seeking to embarrass President Corazon Aquino.

Aquino's 4-month-old government has been laboring, so far unsuccessfully, to open talks with the powerful communist insurgents -- a policy that has led to open frictions between influential Cabinet members and segments of the military, including Defense Minister Juan Ponce Enrile.

A spate of kidnapings by Moslem insurgents could signal a reopening of that front, which has been relatively quiet in recent years, adding to the pressures on Aquino by the military for a generally more active strategy in pursuit of guerrilla forces.

The Moro National Liberation Front, the main Moslem insurgent group, also has split into several factions in recent years. There was a major uprising among the Philippines' 5 million Moslems beginning in 1972 against the government of then-president Ferdinand Marcos. Negotiations later lowered the general level of hostilities, but a final reconciliation has never been reached.

Lawrence was taken from his dormitory room at Mindanao State University in Marawi by about 20 armed men Saturday night, Balbanero told The Associated Press in Zamboanga. The general said Lawrence saw the intruders through the window and hid his wife, Carol Ann, in a cabinet before he was taken away.

U.S. Embassy spokesman Alan Croghan said in Manila that the embassy had been informed of reports of the abduction by the Defense Ministry and was seeking more information.

Lawrence's mother Muriel Lawrence said in Madison, her son and daughter-in-law had written recently that "there was a great deal of ill feelings toward Americans, especially among the Moslem people, since the bombing" of Libya in April by U.S. jets. "We don't know if that was related to this (the abduction). We have not heard," UPI quoted Muriel Lawrence as saying.

She said her son had been in the Philippines for about three years.

The 10 nuns, all members of the Carmelite order, were reported by military sources to have been taken from their convent on Friday night.

The convent is located on a hilltop about two miles from the university.

Bishop Fernando Capalla of the nearby city of Iligan quoted witnesses as saying that the men forced the nuns down from the hilltop, loaded them into several motorboats on Lake Lanao and sped away toward the other end of the lake, UPI said.

"They were taken down through the back door," Capalla said. "There must have been many (boats) because the farmers below the hill said there were many armed men."

Pope John Paul II, speaking in Castelgandolfo, Italy, appealed for the release of the nuns, saying they are "defenseless people, dedicated exclusively to prayer and contemplation, who have become the object of . . . violence and outrage."

As the government wrestled with the insurgency problems, about 300 riot police kept a wary eye on several hundred pro-Marcos demonstrators who had gathered for a rally in downtown Manila's Rizal Park.

A similar rally last week turned into a bid to take over power by Marcos loyalists, led by former vice presidential candidate Arturo Tolentino, supported by several former Marcos generals and about 300 troops. The coup bid fell apart in 36 hours, but Aquino said she would allow no further demonstrations designed to destabilize the government.

Riot police swept through four or five times during the humid, rain-filled day, scattering chanting demonstrators. The police were lightly armed with bamboo and wooden sticks, and one officer said they were under instructions to show maximum restraint, only keeping the demonstrators from gathering in one spot.

Rain and a police sweep late in the day sent the last groups of demonstrators running from the park. No injuries were reported.