It took just three days after the inauguration of Nigeria's first civilian president in 15 years for the issues likely to dominate his term -- nationwide economic collapse, rampant corruption and sporadic civil warfare in the Niger River delta -- to shove to the fore.

Battles in the delta killed about 50 people Sunday and Monday, despite pleas for patience from Olusegun Obasanjo and a promise by some warring militias there to mark his installation with a 30-day truce. The renewed fighting amid the oil fields that provide Nigeria's lifeblood underscores the daily threat that unrest in the delta will pose to Obasanjo's efforts to establish a stable, accountable government in Africa's most populous nation.

On Monday, Obasanjo's office said he had suspended nearly all contracts and licenses issued this year by the previous military government to review "their propriety and relevance." Nigerian media say the military -- whose 15 years in power were marked by rampant corruption -- approved oil exploration licenses, construction contracts and other favors, worth hundreds of millions of dollars, to companies linked to senior officers and their business partners.

Obasanjo's first days in power underscore his need to focus on a few key issues, most of them economic, his spokesman said today. That will mean putting off calls by Nigerian and American democracy advocates for a new constitution to replace the one decreed last month by the military, the spokesman said. U.S. officials suggested that Washington is likely to agree with that decision.

Obasanjo is bustling around Abuja to set up his government. He is expected to open the legislature on Thursday and submit for approval his list of cabinet nominees.

At almost every opportunity, he rails against his declared enemy -- corruption. On Monday he opened a two-week seminar on improving government efficiency for the top civil servants of each ministry. He paced before them with a microphone, preaching like a television evangelist.

Obasanjo attacked "contractors" -- a Nigerian euphemism for officials who set up companies with friends or relatives in charge and award them contracts, at inflated prices, to supply goods or services to state agencies. "Those who are civil servants and at the same time contractors, you must be ready to get out now, because there will be no room for you in this administration," he declared.

Obasanjo's suspension of decisions by the previous military government of Gen. Abdulsalami Abubakar covers all agencies except the judiciary. His office said a committee will be set up immediately to recommend whether to amend or cancel the decisions.

Obasanjo reportedly was angered when Abubakar -- in his last three months -- issued potentially lucrative oil exploration licenses without competitive bidding, named 52 foreign ambassadors and allocated hundreds of millions of dollars for construction and other projects. Each decision was widely attacked as a last-minute way of shunting money or privilege to outgoing officers.

Besides attacking corruption, "our priority must be improving people's lives," especially in the Niger delta, said Obasanjo's press spokesman, Doyin Okupe. Many Nigerian and foreign analysts say that approach is essential to keeping the country stable.

Gen. Sani Abacha, the dictator whose death last year allowed Abubakar to begin the transition to civilian rule, "brought the country pretty close to the brink" of civil upheaval, a Western diplomat said. "We're still close to it. . . . Within the first three months, [Obasanjo] has to be seen doing some good for ordinary people."

In the delta, militias of the Ijaw ethnic group seize oil workers and pumping stations, demanding jobs, roads, electricity and other amenities for their impoverished villages. Or they just demand cash. They also fight other ethnic groups for land and political power. Abubakar slowed, but did not stop, the fighting in recent months by deploying thousands of troops around the swamps.

Amid the national goodwill accompanying Obasanjo's inauguration, several Ijaw militias agreed to a month's halt in attacks on ethnic rivals. But the delta's ethnic militias are splintered, many recognizing no authority.

On Sunday, Ijaw fighters attacked ethnic Itsekiris at the village of Atorun. Nigerian journalists counted hundreds of wounded reaching the town of Warri and quoted witnesses as saying 50 to 60 villagers were killed. Itsekiri youths killed several Ijaws in attacks Monday, media reports said.

The new constitution says the central government will return to each Nigerian region 13 percent of the state revenues it generates, up from 3 percent. But delta people voice nod confidence that this will improve their lives. They noted that years of heavy government spending, ostensibly for development in the delta, have enriched only officials and a few local traditional leaders.

CAPTION: Nigerian President Olusegun Obasanjo will delay replacing the old constitution to address economic issues and the unrest in the oil-rich delta.