By Louis Chude-Sokei, c/o The Los Angeles Times

ALTHOUGH NOT quite able to pass for white, Sen. Barack Obama (D-Ill.) has been able to pass for African American. He is biracial, but not white; black, but not African American; American but not African. What has entranced the country more than his somewhat vague policies is Obama's challenge to conventional racial and cultural categories.

Among African Americans, discussions about his racial identity typically vacillate between the ideologically charged options of "black" versus "not black enough" or between "black" and "black, but not like us."

But there is a third side to Obama — and also to the politics of racial passing in America.

The population of African immigrants in the United States is rapidly growing. Since 1990, about 50,000 Africans have come to the United States annually, more than in any of the peak years of the international slave trade, which was abolished in 1807. They add to the steady influx of black immigrants from other continents and the Caribbean, and those who have been in the United States for generations but who don't racially and culturally define themselves as African American.

These blacks feel cramped by the narrowness of American racial politics, in which "blackness" has not just defined one's skin color but has served as a code word for African American. To be heard and to be counted, these black immigrants must often pass as African American, sometimes against their will.

Obama is not the first prominent black to defy conventional American racial and cultural categories. People identified former Secretary of State Colin L. Powell's Jamaican ancestry as the quality that made his blackness different. When in the mid-1990s it seemed possible that he would run for president, the pride of the Caribbean immigrant community was nearly palpable. He emboldened Caribbean immigrants to resist African American pressures to erase their own cultural and historical distinctiveness.

In such distinctions between black immigrants and African Americans lay buried a history of competitive intra-racial tensions and cultural differences that have never been resolved.

In addition to black immigrants' need to hold onto their own identities, many whites have historically tended to regard black immigrants as a model minority within a troublesome native-born black population. A good proportion of immigrants tend to be better educated than African Americans, don't have the "chip" of racial resentment on their shoulder and exhibit the classic immigrant optimism about assimilation into the mainstream culture. Many whites, however, exploit these differences to magnify the problems of African Americans while avoiding charges of racism. And because these differences often result in greater employment and more educational opportunities for immigrants and their descendants, they also feed tensions between native and immigrant blacks.

The complex history of black immigrant and African American interaction and distinction has been masked by a tendency in American politics to treat "black" and African American as interchangeable categories. It is further masked by an African American cultural politics that arrogates to itself the official word on racial matters. For black immigrants, African American culture can be as alien and as hostile as mainstream America.

Because Powell didn't run for president, the intra-racial differences and historical tensions between immigrant and native-born blacks that his candidacy might have brought to national attention remain largely unknown. "Black" effectively continued to mean African American.

But, from a black immigrant perspective, Obama's run for the presidency carries the promise of spotlighting this "category crisis" at long last. There is the possibility of a conversation in which Africans in the U.S., along with other black immigrant groups, may emerge distinctly from the all-consuming category of "black."

These issues have been present in scholarship and education for some time. Tensions between native and foreign-born blacks are rising in higher education because universities are reputedly using black immigrants, at the expense of the native-born, to diversify their student bodies. In this case, black immigrants are the primary beneficiaries of the blanket category of "black."

Add to this a shifting academic terrain in which traditional black studies are threatened by increasingly popular courses and programs that have a diaspora or Africana slant and do not put African American history or experiences center stage. It's now not uncommon to hear African American scholars and students complaining about the increasing presence of Caribbean and African blacks in black studies departments. Indeed, these kinds of tensions erupted at UC Berkeley two years ago and reflect the continuing struggle over the redefining of "black" in American life and thought.

As the numbers of black immigrants and their progeny grow to challenge the numerical supremacy of the native black minority, can a challenge to African Americans' cultural dominance, racial assumptions and politics be far behind? Especially because black immigrants generally and increasingly differ from native-born African Americans in their views on race, racism and political affiliations. They also are less responsive to American racial traumas, which helps explain why some civil rights leaders are unsure of Obama's loyalties to African American causes. Because his political "blackness" is independent of their sanction and emerges from outside their histories, it threatens their cultural and political authority.

So Obama does not transcend race, as some might dream. Instead, he represents a set of tensions that go beyond black and white. On one hand, there is America's complex and still unresolved relationship with African Americans and, on the other, an emergent black immigrant presence that is less willing to politically or socially pass for "black" and that has unresolved and unspoken issues of its own.

In Obama, we witness how one set of tensions works with and against the other. Immigrant status is deployed not against race but against the messy and unresolved tensions of domestic American racial relationships. And in this, whether he wins or loses, Obama is definitely a sign of the country's future.

LOUIS CHUDE-SOKEI, an associate professor of literature at UC Santa Cruz, is the author of "The Last 'Darky': Bert Williams, Black-on-Black Minstrelsy and the African Diaspora."