Nigeria's armed forces, which have ruled this country for the past 15 years, handed power to elected President Olusegun Obasanjo today, restoring civilian government to an estimated 110 million people -- nearly one in five black Africans.

In a stiff military pageant, Gen. Abdulsalami Abubakar handed the government to Obasanjo, having said in a speech Friday that Nigeria's soldiers, who have conducted six coups and ruled Nigeria for 30 of its 40 years, "must forever resist and renounce the seduction . . . of political power."

Until today, Obasanjo, a former ruling general, had been the only Nigerian leader to hand power back to civilians voluntarily. "The incursion of the military into government has been a disaster," bringing economic collapse and political strife, he said.

The armed forces, however, retain considerable influence, having imposed a constitution that maintains the highly centralized power structure that they built. And Obasanjo's party, which will dominate the legislature, is effectively a coalition of former military officers, many of whom have become rich during their years in power, along with many civilian politicians with ties to past military governments.

Still, Obasanjo's inauguration as only the third elected leader of Nigeria appears to offer the best chance for this powerful, and powerfully unstable, country to build a unifying, democratic government, said ordinary Nigerians and political scholars. The shift to elected government, in the country that dominates West Africa economically and politically, also may represent the most notable advance for democracy on this continent since South Africa threw off apartheid rule in 1994.

South African President Nelson Mandela, Britain's Prince Charles and other world leaders sat behind Obasanjo and Abubakar today, underscoring the importance of a stable Nigeria. Jesse L. Jackson, a Clinton administration envoy for Africa, and Transportation Secretary Rodney E. Slater led the U.S. delegation.

The armed forces, politically discredited for the economic collapse and pervasive corruption under their rule, stepped out of government with a show of dignified pomp. They invited thousands of Nigerian and foreign guests to an asphalt parade ground amid new and half-built government office buildings in this capital, which is still under construction.

Abubakar, 56, arrived in dress uniform to salutes from senior officers and horsemen with sabers. Cannons roared and jet fighters thundered low overhead, streaming smoke in the green and white colors of the Nigerian flag.

Abubakar said this was a day that ranked second for Nigeria only to its independence from Britain. "To us all beckons the historic opportunity to break, once and for all, the cycle of instability and mistrust that have wracked our political life since independence," he declared.

In his inaugural address, Obasanjo, 62, lamented the collapse that has left economic sinews such as the electrical grid, phone system and oil refineries barely functioning. In his government, he vowed, "corruption will be tackled head-on. No society can achieve its full potential if it allows corruption to become the full-blown cancer it has in Nigeria."

But he did not speak of investigating past corruption, in which military rulers have enriched themselves with billions of dollars siphoned from the economy, especially the oil industry.

He warned that his reforms would take time. "I am not a miracle worker," he said. "I'm also going to ask you to make sacrifices and exercise patience. . . . With God as our guide and . . . Nigerians working with me, we shall not fail."

Obasanjo promised revived programs of economic development, especially for the Niger River delta, where impoverished ethnic groups have fought sporadic insurgencies for a share of the oil wealth pumped from beneath their farms and swampland. He also promised to continue Nigerian efforts to negotiate a settlement of the civil war in Sierra Leone, where Nigerian troops form the bulk of a West African peacekeeping force.

A sign of the political revolution accomplished today was the official avoidance of the name of Gen. Sani Abacha, the brutal, corrupt dictator whose death a year ago elevated Abubakar, who began the move to civilian rule. Abacha's erasure from speeches and official media may have eased the departure from powerful positions of many former Abacha aides, who are regarded as corrupt. Within hours of the ceremony, Obasanjo's government announced the replacement of top military officers with those seen as having been apolitical during the military rule.

Obasanjo was a career army officer who was named military ruler in 1976 after his superior was assassinated. He held elections, led the army back to its barracks and retired to a farm. But after other soldiers seized power, Obasanjo publicly condemned military rule, and Abacha jailed him in 1995. After Abacha died last June, Abubakar freed Obasanjo. Powerful men in and around the military -- notably former military ruler Ibrahim Babangida -- urged Obasanjo to run for president as the one man capable of uniting the country.

But political scholars, church leaders and democracy advocates say Obasanjo must accomplish another revolution if he is to bring real democracy and stability. This nation of more than 200 ethnic groups was founded as a loose federation, and has become politically sullen and violent under the military's centralized rule. "What was missing [in Obasanjo's inaugural address] was any statement about opening debate" on decentralizing power in Nigeria, notably by establishing a democratic constitution, said Olisa Agbakoba, a Lagos-based lawyer and civil rights leader.

In his speech, Obasanjo "made the right noises" about fighting corruption and assuring civilian control over the military, Agbakoba said. "But we are watching to see his [cabinet] appointments . . . to see if he will have the guts to break away from" the ex-military people who funded his political party and helped him win power, he added.

Obasanjo "said he needed six months to establish his authority. I think he has a much shorter time. . . . He must start immediately to show his independence" from powerful, retired officers, Agbakoba said.

Across the street from the ceremony was evidence that the handover changes little immediately for most Nigerians. Under a scorching sun, hundreds of people set up an impromptu market, as they do wherever a crowd gathers in Nigeria, hoping to hustle a little money.

Men and women spread plastic sheets on the ground to sell sandals or clothes. A man sold grimy, pirated music cassettes from a rack strapped to the back of his motorcycle. Women edged through masses of gawkers and policemen, selling cold sodas from tubs in hopes of making $5 by day's end.

"The military's departure is a necessary thing," said John Unom, a 39-year-old unemployed teacher who drives a taxi. "We have been disappointed before, when the soldiers left, but then came back. . . . Now, we are still hopeful," he said, but it is a hope of prayer, rather than of probability. "We are like the children of Israel in the Bible, who wandered in the wilderness and had faith that somehow, God would lead them out. This is the kind of hope that Nigerians must have."