Black comedian Eddie Murphy once powdered his face white and set out to discover how the other half -- the white half -- really lives. In a hilarious "Saturday Night Live" sketch, a white shopkeeper insists on giving the powder-white Eddie a free newspaper when they are alone, and a party breaks out among whites on a commuter bus when the last black person gets off.

The gap between black and white has been the stuff of comedy for years, bringing fame to performers from Dick Gregory to Murphy and Richard Pryor. But to Thomas Kochman, an anthropologist at the University of Illinois at Chicago, differences between blacks and whites are a subject of serious study -- and he thinks they are no laughing matter.

The German-born Kochman, a 49-year-old linguist, sociologist and former welfare caseworker, is fascinated by the differences. He believes blacks and whites have sharply contrasting approaches to important issues from politics to power to sex and often fail to recognize it -- which leads to misunderstandings between individuals and to what he sees as a growing divergence between the black and white communities.

A Kochman example:

Jesse Jackson is speaking at a political rally and starts out chanting, "I AM SOMEBODY!" Kochman sees whites in the audience frown. He feels himself pull back.

"I can't believe that academics, black colleagues of mine, can stand up and start shouting, clapping," Kochman says. "In my gut I'm shocked. I'm not used to being brought into a scene that way."

He suggests that a white audience equates emotional involvement with loss of control; such scenes raise the specter of demogoguery to whites -- they suspect a highly charged speaker is trying to manipulate them.

From the black perspective, he says, the impact is very different.

"The sister who faints at the Baptist revival never seems to lose her glasses, so how much control is lost?" he says, adding that blacks are accustomed to dealing with high-energy speakers and are able to look beyond the style to the substance of the message.

"Whether spirited speaking can be manipulated beyond blacks' ability to control it doesn't concern blacks -- it concerns whites who make the ethnocentric judgment that to be emotionally involved with a speaker is to be manipulated," he says.

He points out that posters of Martin Luther King Jr., Malcolm X, Louis Farrakhan and Jackson most often show them with their mouths open, hands extended, emphasizing some point in a speech.

"To blacks that says the man in the picture is powerful, strong, seeking truth by emotionally engaging ideas, taking them on," says Kochman. "Whites have a different perspective . . . they see themselves being harangued."

Chicago Mayor Harold Washington, who feels he has been misunderstood by his city's whites, especially the press, distributed copies of Kochman's book "Black and White Styles in Conflict" to the city hall press corps.

"A careful study of the news coverage of the mayoral campaign and of this administration over the past two years demonstrates the need for all reporters to read this book," the mayor told the journalists, according to Chicago newspapers.

Detroit Mayor Coleman Young sent Kochman a letter telling him he felt his book explained a lot of Young's problems with whites in Detroit.

Kochman's theory is that blacks have a "high offense, high defense" culture, in which aggressive language, cocky behavior and florid clothing are not only accepted but enjoyed as a source of power that "feeds" life. Blacks are able to handle the brashness of such language or behavior in others without losing control or being overwhelmed.

White Americans, in Kochman's view, generally contain differences and anger as well as styles of speech and dress so as not to impose on each other. As a result whites feel threatened or disturbed by displays of anger or ostentatious dress.

For example, he says, blacks make a distinction between arguing and fighting that whites do not. For blacks, verbal confrontation can go a long way before physical confrontation is threatened. "The extreme of arguing is 'woofing,' like Ali and Frazier, like the Black Panthers and Louis Farrakhan," Kochman says. "Whites hear the same words from the same people and think: Fight, danger. Blacks understand woofing is going on. Whites think fight before blacks think fight."

He says, however, that in this case his definition of "white" really applies most to the white Protestant tradition. Ethnic whites, particularly Jews, Irish and Italians, often "love to argue, love to boast and joke," he says. "It is the difference between self-contained cultures and expressive cultures as much as black and white."

The differences apply to private matters as well as to public ones.

Kochman cites the case of a young black woman who complained that a white coworker had put his hand on her thigh after lunch one day without first broaching the subject of his sexual interest.

"Why did he have to be so damn sneaky?" Kochman says she asked.

Yet, he says, from the white perspective there was nothing sneaky about it. The man had offered her rides home, had discussed business projects with her, talked about TV shows and current events, taken her to lunch and often paid the bill. Then came the touching.

"If she had been white the sexual interest would have been implied by his actions," says Kochman, adding that an open discussion of sex would have been considered offensive and pushy. For the black woman, however, an honest discussion would have been preferable to the approach the man took. "To a black woman it is not an offense to have her sexuality acknowledged," he says.

According to Kochman's schematic a black male's more aggressive, verbal approach would have been easier for the black woman to deal with because she would have recognized it as sexual interest and been able to accept or reject appropriately. The more subtle white approach slipped under her radar.

Kochman, a lanky, loose-jointed man with a casual manner, grew up in upper Manhattan. He has never lived in a black neighborhood.

Yet he finds himself teaching blacks and whites about black cultural signals and concedes it makes for tense situations when blacks find themselves being lectured about themselves by a white.

"At one point," he says, "there was a strong sense that I was an interloper in this field. Now I'm accepted as an anomaly . . . "

While teaching at the Northeastern Illinois University's Center for Inner City Studies, he remembers facing a class of 39 black men and women earning their master's degrees in urban education, wondering what this "white boy" was going to tell them about their language.

Two years later, feeling growing tension from black students, he gave up that professorship, handing a course in black English to a black teacher. He began his work as a communications professor at the University of Illinois in 1970. His classes are generally 70 percent white.

He came to this career after working for a year for the New York City welfare department investigating clients' eligibility, a job that took him into black neighborhoods. In 1966 he got a summer job collecting black idiomatic expressions in the Bronx for a study on the "Idiom of the Negro Ghetto."

Fascinated by the work, he went to the Center for Inner City Studies for more work on black American life. That led to his doctorate from New York University in linguistics and sociology. He moved into anthropology as he began to compile and dissect the cultural differences between blacks and whites.

Kochman said he works by observing life in black neighborhoods, among black students and colleagues, and by building networks for interviews and field work among his black contacts.

He acknowledges his ideas have been slow to be accepted in academic circles. The orthodox view, he says, is that blacks have no separate culture, and that differences between black and white behavior are due to the effects of discrimination and poverty on black families.

That approach, he argues, has led not only whites but blacks to assume that discussing differences between them would lead to the conclusion that black behavior is inferior.

"It's the politeness conspiracy," says Kochman, "and it leaves many prejudices in place."

Kochman says his worst moments come when middle-class blacks, interpreting his work as an attempt to show them inferior to whites because they are different, react by saying, "I've never seen blacks act like that."

"That makes whites wonder if I know what the hell I'm talking about," says Kochman. "At that point I have to rely on other black people, even some whites, to say they know the reality I'm referring to but they've never put it into thoughts and words: Black people and white people act differently."

Kochman is now studying how black-white differences affect politics, as part of a broader look at "mainstreaming," or bringing different ethnic and cultural styles together in the American melting pot.

Cultural differences, he says, culminate in the growing divide between black and white political perspectives. The split was highlighted by the last presidential election, when about 90 percent of blacks voting opposed President Reagan while roughly 65 percent of whites voting cast ballots for him, according to an ABC news exit poll.

The heart of the difference in selecting national leaders, according to Kochman, is that blacks treasure boldness and audacity as signs of leadership ability, while in "mainstream American politics," boldness and audacity are taken to mean an individual is not stable, not a team player.

Similar differences in approach extend to black and white professional situations, according to Kochman, and as a result, good workers with the best of intentions often end up at odds when one is black and one is white.

Blacks value confrontation in an office setting as well as at home, Kochman says, as a way of "truth-seeking." To blacks a colleague who will not confront another colleague about a problem is not concerned -- they feel he does not attach importance to either the problem or the other person involved.

But whites, Kochman said, find confrontations and arguments a sign of disunity or conflict in the office. Whites interpret black desire to dispute differences as a troublesome habit even as blacks see it as evidence of caring about producing the best work.

One of Kochman's examples of conflict in the office occurs when two white managers are talking as a black colleague approaches. The two whites finish their conversation before greeting the colleague. The black person considers this behavior rude and is angered before he says anything. This creates distance and tension between the black and the whites. Kochman believes a group of blacks would typically interrupt their conversation to acknowledge a person approaching the group.

This tension results from the practice of whites emphasizing subject matter over personal relationships versus blacks' favoring personal relationship over subject matter.

"That's a cultural clash, a difference in styles," says Kochman. "And it leaves both people offended, and puzzled because they don't appreciate the other cultural perspective."

Kochman argues that cultural differences often confuse attempts to deal with racism on both sides. In his book he cites the example of blacks condemning racist whites before a racially mixed group. Some whites in the group feel uncomfortable and begin to defend themselves as not racists.

"To blacks that itself is evidence that they are racists," says Kochman, "because in black culture a person may speak generally without directing his remarks against the people who are listening. But if those people start to react as if it's about them -- the old saying is 'if the shoe fits, wear it.' "

Recognizing cultural differences may improve understanding, but Kochman acknowledges that this isn't always enough to overcome prejudice. "If a person doesn't know the difference in cultures, that's ignorance," he says. "But if a person knows the difference and still says that the mainstream culture is best, that 'white is right,' then you've got racism."