WHO IS an Asian? What Americans can call themselves Hispanic? Who has the right to call himself disadvantaged? An affirmative-action brouhaha being played out in San Francisco's Fire Department prompts a broader rethinking of this problematic approach to racial justice.
Some of what's being reported is pure ethnic fraud -- white firemen calling themselves black, a Portuguese-American trying to slip by as Asian. More troubling, there's also a new ethnic vigilantism. Certified Hispanics discover themselves relabeled as white and left off fire-department promotion lists. A black woman's ethnicity is questioned because she's light-skinned.
This sudden interest in roots, real and phony, has a simple enough explanation: Jobs are at stake. The temptation to lie outright about one's past has to be great when careers are made to turn, not on personal competence but on ethnic identity. If that's how the game is played, the cynics say, we'll bend the rules.
Factionalism, both between and among racial and ethnic groups, becomes almost inevitable when the fact of being Hispanic or black or Asian means better treatment. That's one reason why, until the mid-1960s, promoting civil rights meant not inquiring whether someone was black or Moslem or Vietnamese.
In San Francisco, the trouble began three years ago when the Fire Department settled a discrimination suit. The department agreed that minorities would receive preferences in hiring and promotion, a common enough way of trying to right past wrongs.
Last year, three self-described Hispanics outscored Capt. Peter Roybal on a civil-service test for promotion. Mr. Roybal, a Mexican-American who needed an affirmative-action nudge to get his promotion, reported them to the Civil Service Commission as fake Hispanics.
From the evidence at hand, one of the three seems to be a phony: A birth certificate identified him as Italian, not Hispanic. But the case against the other two falls into the ethnic-vigilantism category. Although they are certifiably half-Spanish, that doesn't satisfy Mr. Roybal and his colleagues.
Being Spanish isn't really being Hispanic, Mr. Roybal insists. ''I don't know what [Spanish] culture is, other than what I read in National Geographic. They live a totally white life.''
Because these two men haven't segregated themselves, the argument goes, because they've chosen life in the mainstream, because they don't speak Spanish at home -- because they've lived out the classic immigrants' assimilation story -- they don't deserve help.
Now a group of Hispanic fire fighters has gone a step further: They demand the creation of an ethnic-purity panel, composed of a dozen Latinos, to determine who should be entitled those preferences.
Deciding the politically correct way someone must relate to his culture is deeply troubling business. The witch-hunts these fire-fighters engage in -- insisting that everyone's ethnicity be posted, digging up colleagues' birth certificates -- recall the tactics of McCarthyism. There's more unhappy history to recall: a fundamental evil of both Nazism and apartheid is that these regimes also depended on judgments about social ''purity.'' They made people's fates rest on whether they were Jewish or homosexuals or Gypsies, black or colored or white.
Both regimes had their versions of ethnic-purity panels -- and so did Dixie states, back when Jim Crow laws were in effect. A century ago, when a man named Plessy was turned away from a ''white'' railway car in Louisiana because of race, he challenged the infamous regime of ''separate but equal.'' Plessy's initial argument was that, because he was only one-eighth black, he really belonged to the whites' railway car.
There are, of course, good reasons for the kind of deal the San Francisco Fire Department struck for settling its discrimination case -- reasons for singling out and helping those who have been denied jobs in the past. Moreover, categories like race and ethnicity are often the only way to decide who needs that help.
But, as the current squabbling shows, affirmative action is hardly costless. The underlying problem is how to accomplish its goals while minimizing the hypocrisy as well as the racial and ethnic strife.
Whenever preferences are being awarded, whether to decide on university admissions or TV station licenses or job promotions, questions of the ''ethnic purity'' variety seem inevitably to arise. At the University of California, where I teach, discussions about would-be hires sometimes go like this: Does a Korean ''count'' as an Asian, and do Asians ''count'' for affirmative-action purposes? Does the black son of a well-to-do lawyer count the same, for affirmative-action purposes, as the black son of a laborer?
The only really novel element in the proposal by San Francisco's Hispanic fire-fighters is its up-front-ness. It's a reminder that the old civil-rights fighters were right -- that in the long run, we're better off with a genuinely color-blind society than one that approves stereotypes of ethnic purity. Meanwhile, we're better off suffering with a few fake Hispanics than inventing ways to determine other people's roots.
OC Mr. Kirp teaches public policy at the University of California.