Little more than a week after taking office, President Olusegun Obasanjo has begun an overhaul of Nigeria's armed forces, which shattered the country's economy and democratic institutions during 15 years in power.

Obasanjo -- a former general and military ruler -- has named new service chiefs, ordered an investigation into human rights abuses and, according to Nigerian sources, is preparing to purge virtually all officers who played significant roles in the military's corrupt and often brutal reign.

Those moves will solidify Obasanjo's authority over the armed forces and may open the way to prosecuting some figures from the regime of Gen. Sani Abacha, who died a year ago. But Obasanjo's actions will avoid confrontation with an earlier military ruler, Ibrahim Babangida, who remains influential and gave critical support to Obasanjo's presidential campaign.

On Friday, Obasanjo named a commission to investigate human rights abuses -- especially alleged assassinations -- committed since Jan. 1, 1994. His office gave no reason for the cutoff date, but it effectively focuses the inquiry on Abacha's regime and leaves unaddressed reported abuses under Babangida, who ruled from 1985 to 1993.

Many Nigerians have called for Obasanjo to investigate Babangida, especially on corruption charges, but voiced doubt about whether he will comply. Last year, after Obasanjo was freed from three years in prison under Abacha, Babangida pushed him to run for president and rallied other retired military officers to fund his campaign.

Obasanjo appointed a former Supreme Court justice and some of Nigeria's most noted human rights activists -- including the Rev. Matthew Hassan Kukah, a leader of the Roman Catholic Church in Nigeria -- to the human rights investigation. He ordered them to identify "the person or persons . . . [who] may be held accountable" for human rights violations, notably assassinations.

Abacha's opponents and Nigerian journalists accuse the Abacha regime of killing dissidents, most prominently Kudirat Abiola, a democracy activist and wife of Abacha's most popular political opponent, Moshood Abiola. Gunmen ambushed Kudirat Abiola in her car in Lagos in 1996.

"We welcome the decision to investigate . . . but it needed to have [included] the entire 15 years" of recent military rule, said Clement Nwankwo, head of the Lagos-based Constitutional Rights Project.

On May 29, as the military handed back power in popular disgrace, Obasanjo vowed to restore its professionalism and end its proclivity for staging coups. Since Nigeria's independence in 1960, officers have changed the regime seven times by coup or assassination, while only three governments have been elected.

Obasanjo's aides are preparing a list of hundreds of officers -- out of a corps of perhaps 6,000 -- to be retired, said a Nigerian military source who asked not to be named. The military is estimated to number 80,000 soldiers, although Nigerian and Western analysts say thousands probably are "ghosts" -- troops who don't exist, but whose paychecks are collected by corrupt officers.

"All officers who served for six months or more in political posts" -- as ministers, state governors, heads of government agencies and state-owned companies -- will get retirement orders, the source said. Lower-ranking officers who served as aides or assistants to those men will get them, too, sources said.

Obasanjo and his new military chiefs are expected to conduct the purge quickly. "I would be surprised if we don't see this weeding out done within two months," said Anselm Okolo, an editor in Abuja, the capital, for the Nigerian weekly news magazine, Tell.

Nigerians' worries of a military coup have eased with Obasanjo's inauguration. After Abacha's death last June 8, his successor, Gen. Abdulsalami Abubakar, retired Abacha's closest aides and led the shift to elected rule. More senior figures from the Abacha years resigned on May 29 with Abubakar.

Within hours of taking office, Obasanjo named chiefs of the Nigerian army, navy and air force who never had held political posts.

The new president -- who ruled in the late 1970s and then handed power back to civilians -- declared in his inaugural address that, "as a retired officer, my heart bleeds to see the degradation in the proficiency of the military. A great deal of reorientation has to be undertaken" including "retraining and reeducation . . . to ensure that the military submits to civil authority and regains its pride, professionalism and traditions."

In Nigeria's public debate over just how democratic their country has become following the handover to Obasanjo, Babangida's influence is one of the most controversial points. Babangida, a northerner, is widely disliked -- especially in the south -- for alleged corruption while in power and for having reneged on his promise to return power to civilians in 1993.

His central role in funding Obasanjo's campaign "doesn't guarantee . . . influence" in policy making, said Obasanjo's spokesman, Doyin Okupe. "Everybody knows that Obasanjo is a robustly opinionated person who will follow his own counsel."

Still, analysts say, Babangida may have achieved some protection against investigations of his rule, notably because some of his former top aides are in Obasanjo's inner cabinet. Obasanjo named one former Babangida deputy, retired Lt. Gen. Aliyu Muhammad, as his national security adviser, and is widely expected to name another, Theophilus Danjuma, as defense minister.

CAPTION: Olusegun Obasanjo names panel to investigate human rights abuses.