Mwendaga Jibo's bleary eyes, rumpled suit, loosened tie and clinging perspiration-soaked shirt attested to the pace of independent black Africa's major political event today -- the impending return to civilian government in Nigeria after almost 13 years of military rule, and a tragic civil war.

Minutes before, Jibo had dragged himself into a friend's air-conditioned apartment from the clammy humidity of nighttime Lagos and collapsed on a couch, the picture of a frazzled politician after long hours on the stump.

Jibo was a teenage high school student when domestic turmoil ended civilian rule in Nigeria's first military coup in January 1966, six years after independence from Britain. Now, at 28, he is learning the grinding routine of political organizing.

"I didn't know what I was getting into, a hoarse-voiced Jibo said. "I saw my family yesterday for only a short time and then I fell asleep in the chair."

Two minutes later, Jibo fell into another deep sleep.

Since September, when Nigeria's Supreme Military Council lifted a ban on political activity, Jibo and hundreds like him have been criss-crossing the countryside of this largest of black nations, organizing political parties for elections next year on which a large measure of Nigeria's future rides with, in some respects, that of black Africa.

On a continent where one-party states and military governments are the rule, Nigerians are very conscious of the impact of their efforts to return to democratic politics. An influential adviser to the military government said the transistion is part of Nigeria's responsibility to blacks in all of Africa and even the world.

"A lot of people are watching nigeria's transition," added the adviser, Bolaji Akinyemi, director of the Institute of International Affairs, Nigeria's foreign policy think tank. "We're corrving the black man's burden now."

Exaggeration perhaps, but Nigeria is indeed considered black Africa's most important state. It has the largest population, 80 million persons in an area the size of California, Nevada and Arizona combined. One of every four black Africans lives in Nigeria.

After Saudi Arabia, Nigeria is the second supplier of oil to the United States, exporting $6.2 billion worth to U.S. buyers in 1977 and leaving Washington with a $5 billion trade deficit with this potentially rich country.

Through grants of money and arms to black nationalist guerrilla movements in southern Africa, Nigerians exert strong political influence on their actions. Aware of Nigerian power, U.S. diplomats openly court the help of Lagos for Western attempts to bring majority rule to such whiteruled states as Rhodesia and Namibia.

Sobered by the point man role, Nigeria's military leaders are cautiously attempting to bring their own often divided countrymen to 20th Century national cohesion -- not without some apprehensions.

In a speech lifting the political ban, Nigeria's blunt-spoken military head of state, Lt. Gen. Olusegun Obasanjo, alluded to the country's turbulent past and the dangers facing it during the political ferments he has opened up.

"Political recruitment and subsequent political support which are based on tribal, religious and linguistic sentiments contributed largely to our past misfortunes," he said. "They must not be allowed to spring up again.

"Let our past experience enrich and enlighten our future: We cannot afford to disappoint Nigeria, Africa and the world."

The lure of political office has rejuvenated Nigeria's experienced politicians, known locally as "the old brigade." They are taking leading roles in many new political parties, of which 40 bad entered the fray by last month.

Five sets of state and federal elections are scheduled over the next year, beginning in April. The military is pledged to hand over power formally to a civilian government by Oct. 1.

The Nigerians have jettisoned the regional parliamentary government they inherited from the British colonial administration. Instead, they have adopted an American-style political model dividing the country into 19 states with a 95-member senate, 450-member house of representatives, an independent judiciary and an executive president.

How this model will work in a country marked by sharp ethnic and religious differences is the unanswered question on the lips of many Nigerians.

Spread through 357,000 square miles of tropical coastline and rainforest in the sough, central grassland plateaus and semiarid desert in the north are 250 ethnic groups. The three largest are the Hausa-Fulani in the north, the Ibo in the southeast and Yoruba in the southwest.

Forty-seven percent of the population is Moslem and 34 percent Christian, while the remainder follow traditional African religions.

These divisions gave birth to the Ibo secession attempt that ended in 1970 with the rebels' defeat after a 30-month civil war that cost an estimated 2 million lives.

The federal victory has left bitter memories. But a grudging acceptance has since then grown up in most Nigerians that the country will remain unified, according to an editor of the Daily Times, Nigeria's leading newspaper.

"Our experlence was much like yours in the States," he said. "Time will take care of the wounds."

Before the political ban was lifted, a 230-member elected constituent assembly, meeting much like America's founding fathers two centuries ago, labored for nine months over a new constitution.

One potentially explosive two-week wrangle developed when about 90 northern Moslem delegates walked out and refused to return until other Moslem delegates and most of the Christian delegates from southern Nigeria would agree to creation of a federal Sharia Islamic appeals court.

Sharia courts, based on principles of the Koran, the Moslem holy book, have always existed in Nigeria alongside government courts, but not on the federal level. Some Moslems and a majority of Christians in the assembly balked at creaating a new role for the religious courts, creating an emotional impasse.

Obasanjo "stepped in, reminded all of them of their national duty, banged some heads together and they went back to work," said a Nigerian political observer. "The issue has been dropped for now, but watch for it to come up again."

While he praised the delegates for reaching a consensus on the constitution, Obasanjo said their deliberations "indicated the practice of horsetrading, shifting alliances, sectional interests and petty loyalty."

The discussions outside the assembly meetings "as well as the political language of would-be participants have shown some ugly signs of things to come," Obasanjo warned.

To combat regional and tribal loyalities, Michael Ani, chairman of Nigeria's Federal Electoral Commission, will register each party only after ensuring it has functioning branches in 13 of the 19 states.

"I have no idea how many of them will make it, but those that do must be national in character." said Ani. "What plagued our parties in the past was that they were tribal, regional and religious."

Ani's commission has registered 47.5 million voters, over half of whom are women, all over 18. There will be 125,000 polling places, he said.

"I am optimistic about the outcome," continued Ani."I do not anticipate violence. Mind you, there may be skirmishes here and there, but not on a scale to prevent the elections."

Informed Nigerians say only five of the 40-odd parties that have sprung up have a real chance of meeting the electoral commission criteria and fielding candidates for the elections:

The Nigerian People's Party, headed by Nnamdi Azikiwe, Nigeria's first president after independence.

The Unity Party of Nigeria, headed by Obafemi Awolowo, a populist and the key opposition leader in the first republic.

The People's Redemption Party, run by maverick socialist Aminu Kano.

The National Party of Nigeria, headed by Shehu Shagari, another politician out of the past.

The Great Nigerian People's Party of Waziri Ibrahim, an "up by the bootstraps" businessman making his first political bid as presidential candidate.

"We expect to be successful and then there will be a lot of pressure on other African states" to follow Nigeria's lead, said Akinyemi of the foreign policy institute. "The African people of other countries will use Nigeria as an example."