Louis Farrakhan, the departing leader of the Nation of Islam, gave what was billed as his last major public address here on Sunday, with his extended illness throwing into sharp focus the question of whether the group will shift toward more mainstream Islamic teachings to survive once it loses its central charismatic figure.

Mr. Farrakhan, 73, looking fairly robust for a man who emerged from major surgery six weeks ago, spent most of his two-hour address denouncing the war in Iraq and calling for the impeachment of President Bush.

“If you don’t want to impeach him,” Mr. Farrakhan said, “censure him, say to the world something went wrong with our leadership and we repent after our wrongdoing.”

He also made an appeal for religious unity in the address before thousands at Ford Field, home to the Detroit Lions football team, capping an annual convention of Nation of Islam members.

It was his first major speech since August, when health problems forced him to turn over control of the Nation of Islam to an executive committee. His health problems stemmed from radiation seeds implanted a decade ago to combat prostate cancer, said Ishmael Muhammad, the organization’s national assistant minister. The treatment obliterated the cancer but also damaged nearby organs.

Given his age and health problems, and the lack of an obvious successor, questions loom large about the future and direction of the Nation of Islam.

Nation members dismiss the notion that the organization’s viability is linked to one man. But academic experts and Muslim leaders say they believe that without Mr. Farrakhan’s leadership, the Nation — which has been divided over its teachings in the past — will shrink even more dramatically unless it shifts toward mainstream Islam’s beliefs.

The 77-year-old Nation of Islam once enjoyed a near monopoly over interpreting Islam for black Americans, using the faith as a vehicle to promote black separatism.

But it now competes with sects that branched away, and with groups ascribing to the more traditional and inclusive Islam followed by millions of Muslim immigrants and their offspring.

Along with a significant bloc of former Nation members, many of these Muslim branches oppose crucial aspects of the organization’s beliefs, which some consider blasphemy.

Leadership changes have altered the Nation’s direction in the past. Elijah Muhammad, the organization’s leader for more than 40 years until his death in 1975, was succeeded by one of his sons, Warith Deen, who broke with his father over the issue of Islamic orthodoxy (and changed his last name to Mohammed). Following Warith Deen Mohammed, this branch embraced diversity and traditional Sunni Islam’s teachings on unity.

Although members of his branch and Mr. Farrakhan’s now profess to respect each other and display less public animosity than in the early days of their split, they still spar over their beliefs.

Imam Muhammad Siddeeq, an Indianapolis cleric and senior aide to Mr. Mohammed, said that for the Nation of Islam to survive, it must turn more toward mainstream Islam.

“In the final analysis they have no option but to move in the direction we are or to just dissipate or disappear,” Mr. Siddeeq said. “This community is going to reconcile itself to pure Islam and reconcile itself to being American citizens who are part of a multicultural society.”

He echoes many others in arguing that the Nation should abandon some of its teachings. The Nation holds, among other teachings, that the group’s founder, W. Fard Muhammad, was the Mahdi, or savior, sent by God to Detroit around 1930 and that spaceships hovering above the earth will eventually play a major role in smiting sinners and rescuing the righteous.

“Those are ideas for kindergarten, a trip to Oz,” Mr. Siddeeq said. “Those are not ideas for people living in the real world.”

Ishmael Muhammad, 42, the Nation’s national assistant minister, who said he was among the youngest of Elijah Muhammad’s 21 children, said the Nation’s message of social reform still resonated, especially its call for black economic empowerment.

“There are a few black politicians and a few millionaires and a couple billionaires, but the fact is that our people are dying,” he said in an interview. “Our struggle to integrate and be accepted has left the masses behind.”

Ishmael Muhammad has sometimes been named as a possible successor to Mr. Farrakhan, as have a couple of Mr. Farrakhan’s sons, but none of them enjoy the same wide following as the departing leader.

But Ishmael Muhammad responds that the era of charismatic leaders is over — that one main goal of the Nation is teaching people to be self-sufficient, particularly in their relationship to God.

Despite his frail health, Mr. Farrakhan on Sunday demonstrated the same passion that has held followers rapt and angered his detractors. He assailed the Bush administration for the war in Iraq, which he said was built on lies and had caused great suffering and disunity.

“Sunni and Shiite lived together, Christian and Jews lived together in Iraq, you didn’t hear none of this stuff before America came in,” Mr. Farrakhan said. “There was no bombing of Shiite holy places. You don’t need to look at Shiite and Sunni, you need to look at those who came in. After they came in all hell broke loose.”

Mr. Farrakhan also urged young black Americans not to join the military.

“I am telling you brother and sister that will be the worst mistake you make to join the military today, because you will leave America in one way and you will come back in another,” he said.

Back in the 1950s and ’60s, as the battle for civil rights was growing, the separatist message, and storied converts like Malcolm X and Muhammad Ali, won the Nation a broad appeal. But Malcolm X quit the movement and was eventually assassinated by Nation members in a fight provoked partly over Islamic orthodoxy.

“We could not continue on this Black supremacist line and be Muslims, be part of the world community of Islam,” said Imam Faheem Shuaibe of the Masjidul Waritheen in Oakland, Calif. “When you say Muhammad is the messenger of God, but you mean Elijah Muhammad, it doesn’t work.”

Reliable statistics are very hard to come by for Muslims in the United States, but the middle range puts the population around six million; some 40 percent of them are African-Americans, a majority of whom follow Warith Deen Mohammed, experts said.

The Nation of Islam will not specify its membership numbers. But Lawrence A. Mamiya, a professor of religion and African studies at Vassar College, puts the number around 50,000, with an ardent following in prisons, where the emphasis on black identity and the struggle against racism, he said, have a pervasive appeal. There are also small branches scattered around the world, particularly in England and the Caribbean.

Breaking away from Warith Deen Mohammed’s reforms, Mr. Farrakhan began rebuilding the Nation based upon its original principles in 1978. He introduced stricter Islamic precepts into the Nation, including prayer five times a day. Members hold that they are just as Muslim as any of the faithful, indeed that North American black slaves were a kind of lost tribe of Muslims forgotten by the faith’s mainstream.

But along with his reforms, Mr. Farrakhan gained notoriety and drew widespread criticism for speeches that were deemed racist against whites, particularly Jews.

In 1995, he organized the Million Man March on Washington, and although he failed to translate that into a sustainable political movement, he became one of the few leaders who appealed to a wide spectrum of black Americans.

Academics who study Islam in America suggest that the followers of Mr. Farrakhan and Warith Deen Mohammed will eventually gravitate elsewhere.

One possible national leader is Siraj Wahhaj, an imam based in Brooklyn. He quit the Nation years ago but came to the convention here to lead Friday prayers, urging Muslim unity in a sermon liberally sprinkled with quotes from the Koran in fluent Arabic.

Many immigrant Muslims question whether Nation members should be called Muslims. Even the followers of Warith Deen Mohammed are criticized by some for giving more weight to his pronouncements than to the holy texts.

“They still haven’t reached the point where there is no color,” said Yassir Chadly, an imam based in Oakland, who immigrated from Morocco 30 years ago. “Islam is universal; it can’t be cut into little sections.”

Such statements make followers of the Nation bristle.

“We are not imitators of Arab culture; that would put us in an inferior position and make them our superiors,” said Muhammad Muhammad, a 40-year-old adherent from Oklahoma City.

In the long run, academic experts said, it is the debate over religion that will most likely relegate the organization to a marginal position after Mr. Farrakhan is gone.

“He talked black, but to join his organization you had to commit yourself to his religion, and the religion has a lot of quirks in it,” said Ihsan Bagby, an associate professor of Arabic and Islamic studies at the University of Kentucky.

Mr. Bagby said that younger Nation members and potential members might find it hard to accept all of the branch’s teachings. “They are realizing that you can be committed to the black community and have a black agenda and still be a Sunni Muslim.”

Copyright 2007 The New York Times Company