In the competitive heat of the second national election campaign since civilian government was reinstituted four years ago, Nigeria appears to be moving away from the traditional African maelstrom of ethnic-centered politics toward the more mundane concerns of personalities and performance.

The shift has been most noticeable in the hemorrhage of defections from the ethnically monolithic Yoruba people's Unity Party of Nigeria and the "wild card" entry into national politics of the Ibo people's defeated but popular former military leader of secessionist Biafra, Chukwuemeka Odumegwu-Ojukwu.

Even so, ethnic, regional and clan considerations among Nigeria's 100 million people will probably determine the politicians' initial constituency base as well as the overall outcome of elections for generations to come.

And the winner-take-all, uncompromising, rough-and-tumble anarchy that so marred past political contests persists. This trait worries the country's 58-year-old president, Shehu Shagari, who is running for reelection.

"Many politicians unfortunately tend to have forgotten what had led to the demise of the first" civilian government, Shagari said in a recently published interview, referring to the collapse of Nigeria's post-independence government after blatant vote-rigging spawned widespread violence.

"Some seem to be going back to the same old game of trying to destroy one another," he added.

Two of Nigeria's leading politicians whose names are inextricable from Nigerian politics of the 1960s, Obafemi Awolowo, 74, and Nnamdi Azikiwe, 78, are Shagari's strongest rivals for the presidency. But their old, formerly solid ethnic bases of support, among the Yoruba and Ibo, respectively, have begun to erode.

Even in 1979 the spread of votes among three political parties in northern Nigeria, a mainly Moslem area dominated by the Hausa-Fulani people, was evident. The People's Redemption Party and the Great Nigerian People's Party made significant headway among northerners whose votes were once thought to be solidly for Shagari's National Party of Nigeria. Shagari is a member of northern Fulani nobility.

Significantly, after 1979 both the People's Redemption Party and the Great Nigerian People's Party splintered into warring factions when their old-style political leaders, Aminu Kano, 62, and Waziri Ibrahim, 57, tried to dictate party policy to a younger generation of officeholders.

The younger men's rebellion and the subsequent fragmentation have reduced both parties to weak regional movements.

An almost identical replay is now wending through the Yoruba-based Unity Party, and the Ibos' old-line political leadership is under attack from the 49-year-old former civil war leader, Ojukwu.

After 12 1/2 years in exile in neighboring Ivory Coast, he returned last June to a tumultuous welcome from the Ibos after receiving a presidential pardon for rebellion charges.

Nigeria's second effort at democratic government is closely monitored on this continent of 400 million people--one of every four of whom is a Nigerian.

The country's oil wealth, despite the economic nosedive caused by a worldwide petroleum glut, has made it one of black Africa's leading economic powers.

Shortly after independence in 1960, its Westminster parliamentary government of colonial days proved to be unworkable in the volatile mix of 250 ethnic groups, although 60 percent of the population is made up of the three major groups--the Hausa-Fulani, Yoruba and Ibo.

Political thuggery led to disorder. After 1966, Nigeria went through three bloody coups, an attempted coup and two massacres of thousands of Ibos followed by a 2 1/2-year civil war in which a million people died. The Army handed back power to the civilians in 1979, nine years after the civil war.

Today Nigeria is governed under a new federal constitution, modeled, in part, after that of the United States. Five state and federal elections are to be held this summer, but a voter registration exercise last August has been widely criticized as sloppy and fraudulent, with many demands that the elections be postponed.

However, Nigeria's transportation minister and one of Shagari's key advisers, Umaru Dikko, said in an interview, "It is our determination to see that elections are held, no matter who does not want it." The government "will do everything within its power to help insure smooth, free and fair elections," he added.

Shagari, who received the widest spread of votes across ethnic lines of five presidential candidates in 1979, would win by even larger margins if the vote were today, said several western diplomatic observers.

The National Party's appeal originally was seen by many here as limited to the Hausa-Fulanis, but Shagari's government "has been good at spreading the pork-barrel projects" and highly sought-after development projects throughout the 19 states, said one diplomatic observer.

"No governor from whatever party has been able to support the claim that he did not get a fair share of federal revenues when the government was flush with oil earnings ," the source added.

A much publicized effort to form an anti-National Party coalition between Awolowo's Unity Party in northwestern Nigeria and Azikiwe's Nigerian People's Party in the southeast foundered on the men's deep mutual mistrust. The two are longtime political enemies.

Awolowo ran second to Shagari in 1979, and the Unity Party captured five, mainly Yoruba, states. But since January the party has been rent by defections to Shagari's more cosmopolitan National Party.

The exodus began over Awolowo's renowned inflexibility on party policies and selection of candidates.

Azikiwe's leadership, on the other hand, is being challenged in Ibo areas by Ojukwu. The men's relationship is strained over Azikiwe's disavowal of the breakaway Ibo state of Biafra, which Ojukwu led, midway through the civil war. Ojukwu joined Shagari's party in January, was elevated to a vice chairmanship and has hinted that he will run as a senatorial candidate this year.

Ojukwu's current campaigning for Shagari is seen as a National Party strategy to pull the Ibos out of the orbit of Azikiwe and the Nigerian People's Party. The more cynical see it as a payoff from the still-popular Ojukwu to Shagari for the pardon.

"There is no element of truth whatever in the charge that Ojukwu's pardon was conditional to his joining" the National Party, said Dikko, who is slated to be the Shagari's campaign manager.

Whatever the outcome of Nigeria's elections this summer, it is clear that much of the past in Nigerian politics still exists, but as the clearly defined appeal of an aging generation of politicians fades, much is rapidly changing.