The former rebel officer who led Nigeria's Ibos into the bloody Biafran secession attempt 16 years ago is trying to woo them back into the fold of national political life.

C. Odumegwu Ojukwu, in his effort to pull fellow Ibos out of what he calls the "siege mentality" resulting from their 1970 defeat in the civil war, has joined a political battle for leadership of the group. His rival is the venerated father of Nigerian nationalism, Nnamdi Azikiwe, the country's first president, who now is seen more as a sectarian Ibo leader.

If Ojukwu, 49, succeeds by force of personality in convincing large numbers of Ibos to join him and vote for the dominant National Party of Nigeria in federal and state elections this August, the switch could dramatically reduce the divisions in this pivotal nation for years to come.

Nigeria's four-year-old constitution is partly modeled on that of the United States. A shift by the Ibos could accelerate the move away from the present six-party turbulence and toward a steadier two-party system--since other parties and groups would be under pressure to coalesce into a single party to offset the National Party's growing power.

Ojukwu unsettled old-line Ibo leadership when he did not rush to join their Ibo-based, Azikiwe-led Nigerian People's Party when he returned from 12 years of exile under a presidential pardon last June. He received a tumultuous welcome from the Ibos. In a January speech in the Ibo heartland commercial city of Aba he appealed to a huge crowd to forsake ethnic allegiances by following him into the cosmopolitan National Party.

Nigeria's two other major ethnic groups, the Yoruba and the Hausa-Fulani, are already substantially resented in the National Party, as are numerous minority tribes. The three main groups represent 60 percent of the estimated 100 million population.

Much of Ojukwu's popular appeal rests on his role as the Ibos' leader during the 2 1/2-year Biafran secession from Nigeria following massacres of Ibos in northern Nigeria in 1966. In 1979 elections, Azikiwe captured the overwhelming support of the Ibos for the People's Party. But in his bid that year for the presidency, Azikiwe placed a distant third among five candidates.

While Ojukwu has announced his candidacy for the Senate and Azikiwe, now 78, is again campaigning for president, each is backing separate candidates for the Anambra state gubernatorial race. Of Nigeria's 19 states, Anambra and one other are predominantly Ibo.

If Ojukwu's candidate wins, then Ojukwu is expected to move into the National Party with Ibo support. If Azikiwe defeats the Ojukwu challenge, the Ibo-based People's Party is likely to keep its hold on Iboland and retain its provincial character.

During a brief meeting in this capital of Anambra state, Ojukwu declined for the third time in 15 months to be interviewed on his return to Nigeria or his political shift.

Ojukwu looked years younger than he had during the last years of his exile in the Ivory Coast. "I'm enjoying what I'm doing," he explained.

Ojukwu's move to the center stage of Nigerian politics can be explained in terms of the Ibo people's "world view," according to Chinua Achebe, a noted novelist. "An Ibo's inner spirit pushes him to struggle for individiual achievement whatever the obstacles imposed by others, whatever the odds or whatever are the fates that face him. The Ibos are not easily cowed by adversity."

Since Ojukwu announced his membership in the National Party in the January speech, he has come under fierce attack from fellow Ibos but not directly from Azikiwe, who takes an elder-statesman role.

In a recent front-page story in the Sunday Satellite, a newspaper controlled by the family of current Anambra governor Jim Nwobodo, an ally of Azikiwe, Ojukwu was accused of embezzlement at the end of the war. His accuser was the former chief of the Biafran Army, Alexander Madiebo.

"I don't believe Ojukwu is an embezzler," responded Achebe, who as a member of the small People's Redemption Party is also a political opponent of Ojukwu. As the son of a millionaire, Ojukwu "went out of his way to lose all the property and money he owned" during the conflict, Achebe added.

"What is happening is Ojukwu is edging himself into the center of things" and is making Azikiwe's political allies "uneasy," Achebe said.

In his speech, Ojukwu answered the critics who had advised him not to get into the rough-and-tumble of partisan politics. "At 49, I shall not leave the field when men of 70-plus consider themselves in their heyday," he said.

In a direct attack on the Ibo-based People's Party, Ojukwu told the huge crowd of Ibos that "it is constitutionally invalid to seek to found an Ibo political party. Politically, it is lunatic to do so.

"Separatism, founded on a siege mentality that erupts in confrontation with everything non-Ibo, is no road," Ojukwu said. "It will lead to isolation, political arthritis and hence defeat."

The question is how many were convinced. "Ojukwu's name is legend but he's never done the village-to-village type of campaigning until now," Achebe said. "He may fail," the writer said. "He may do well."