Church bells pealed across Lisbon Friday as the leaders of Angola's two warring factions signed a peace treaty ending a 16-year civil war that devastated their southern African nation.

The pact culminated more than a year of negotiations led by the Soviet Union, which had backed the leftist government, and by the United States, which had funded the rebels.A provisional cease-fire has been in effect in Angola since May 15, and the last Cuban troops, sent in to back the government, left last week.

Angolan President Jose Eduardo dos Santos and Jonas Savimbi, leader of the Union for the Total Independence of Angola, shook hands and signed the peace accord, touching off applause and cheering among those witnessing the ceremony at the 18th century Necessidades Palace.

Prime Minister Anibal Cavaco Silva said the Portuguese government, which hosted a year of talks preceding Friday's agreement, would do everything possible to see that peace held in the former Portuguese colony.

"We have sowed the seed of peace," Dos Santos said. "But for the tree to grow, we must nurture it."

Savimbi, UNITA founder, said the two Angolan leaders' "most important task is making the Angolan people believe in peace. There is no more reason for war."

The peace accord sets elections for the fall of 1992. It also demands an internationally monitored cease-fire and freedom of the press in the nation of 10 million people that is three times the size of France.

On Thursday, the U.N. Security Council voted unanimously to increase from 60 to 350 the number of military observers who will begin to monitor the cease-fire next week.

Portugal, along with the United States and Soviet Union - who fueled the civil war with arms supplies to their Angolan proxies - will join representatives from the two sides on the U.N. verification commission.

Secretary of State James A. Baker III and Soviet Foreign Minister Alexander Bessmertnykh were among those attending the ceremony.

"All of Africa and all the world bear witness to what we do here today," Baker said. "It is indeed a pivotal moment for Angola and for stability in southern Africa."

He also expressed appreciation to Bessmertnykh for his cooperation in bringing about the peace settlement.

The agreement brings an end to the $60 million a year in military aid the United States has been sending to the UNITA rebels.

The United States says it will continue non-lethal assistance to UNITA until elections slated for late next year, as well as the humanitarian assistance begun several months ago to feed Angolans suffering from famine brought about by widespread drought.

The Angolan conflict, one of Africa's longest and bloodiest civil wars, grew out of the chaotic end to Portuguese rule in Africa in 1975.

It has left some 300,000 dead and crippled the economy of one of Africa's potentially richest nations.

The Cubans joined Angolan government forces pitted against South African troops that invaded Angola to back Savimbi's UNITA.

The thawing of the Cold War and increased superpower cooperation paved the way for an end to the fighting, as the Angolan government shed its Marxist ideology and accepted multiparty democracy.