My mother, Lillian Gadison Brown, always wanted a Cadillac, but she couldn't find a dealership that would sell her one -- not in segregated New Orleans, anyway.

She was black. And in the 1950s and 1960s, the few blacks entering Cadillac dealerships in New Orleans tended to be the people who cleaned those places.

My mother was a professional. That is, she belonged to what was known in black New Orleans as a "professional family." Her husband was a teacher who did some occasional biological research for the National Science Foundation. But that wasn't enough to get her respectful passage through the doors of local Cadillac dealerships, where some salespeople laughed at her outright, or directed her to a used-car lot to shop for battered Chevrolets.

So my mother did the next best thing. She bought a Cadillac from a rich white man in nearby Metairie, La., for what she deemed a "good price." It was a 1965 Cadillac Coupe DeVille, midnight blue with a cream white top, white leather interior and whitewall tires.

My mother cleaned that car weekly -- at least, she ordered her children to wash, wax and polish it ("With clean, soft cloths, please. Don't scratch my car!"). And when she stepped into that sparkling Caddy, she would become a black Cinderella en route to a ball, even though her destination was Schwegmann's supermarket in east New Orleans.

Many blacks in New Orleans and around the United States, including people with more money than my mother, bought their Cadillacs and other expensive cars -- Packards, Lincolns and Chrysler New Yorkers -- secondhand from whites.

Sometimes, those blacks actually bought their luxury cars new by paying white buyers, "front men," to shop for them.

The roundabout purchases stemmed from the market precepts of the time. General Motors Corp.'s Cadillac Division billed itself as "the standard" of automotive excellence. Blacks, by virtue of their social and economic standing in pre-civil-rights America, were regarded as anything but excellent.

Through much of the 1930s, Cadillac had an unwritten policy of not selling to blacks, according to automotive historian Leon Mandel, author of the book "American Cars," and John Steele Gordon, who wrote on the subject in the November 1995 issue of American Heritage magazine.

"Cadillac was after the prestige market,' and part of its strategy to capture that market was its refusal to sell to blacks," Gordon wrote in an article that is now being distributed by Cadillac.

Nowadays, Cadillac is still after the "prestige market." But the car division and its parent company have undergone a cultural revolution in the last decade. In the process, Cadillac has reexamined its notion of prestige.

Simply put, "prestige" is now market share, said Charles Carridine, a black, 45-year-old Detroit native and marketing executive who serves as co-chairman of what Cadillac calls its "diversity marketing program."

Carridine said his parents, too, encountered problems in trying to purchase Cadillacs. "But now we're leading the automotive industry in diversity marketing. We're going to be used as the template for all of GM's marketing strategies in reaching out to African Americans, Hispanics, women and people with disabilities," Carridine said.

What's changed is that General Motors has decided to pay attention to what Cadillac service manager Nicholas Dreystadt tried to tell the company in the 1930s.

Dreystadt noticed that affluent blacks who never appeared in Cadillac new-car showrooms were bringing their cars in for service. He discovered that many of those black-owned Caddies were bought by white front men. Dreystadt urged GM's top executives to begin marketing Cadillacs directly to blacks, or to at least allow them to come into the showrooms.

GM and Cadillac accepted Dreystadt's suggestion, a move that helped to boost Cadillac sales in the mid-and-late 1930s, in the midst of the Great Depression. Dreystadt was promoted to general manager of the Cadillac Division. White Excellence'

But with a resurgence of the economy in post-World War II America came a resurgence of ethnocentrism that once again defined excellence as white, as evidenced by all of Cadillac's print and television advertisements of the period. Not one of those hundreds of ads showed blacks -- or members of any other minority group, for that matter -- buying or owning Cadillac cars.

Certainly, Cadillac was not alone in exclusionary advertising. Practically all of the automotive advertisements of the 1940s through the 1970s showed whites only.

"That was the history. That was the way we were," said William J. O'Neill, a former Cadillac spokesman who now handles public relations for GM's Chevrolet Division.

Explained O'Neill: "There are now 36 million owners of Chevrolet/Geo cars and trucks. In the past, in our eyes, we probably would have classified all of those people as looking alike -- essentially white and Midwestern.

"Well, we've changed," O'Neill said. "We've done research. We now realize that not only do those people not look alike, but they don't always speak the same language; nor do they shop for vehicles or look at products the same way, or have the same values."

But all of those people do have one thing in common: "They all want cars and trucks, and we want to be the people to sell them those cars and trucks," O'Neill said.

Reaching all of those different groups, speaking directly to them, is important for any automaker trying to make headway in a U.S. auto market that is growing by a scant 0.5 percent annually, said Thad Malesh, a senior consultant and analyst at J.D. Power and Associates, a market research firm in Agoura Hills, Calif.

"They're facing economic reality," Malesh said of the automakers' diversity marketing efforts. "They're in an environment where overall auto sales can't grow a great deal, which means they have to increase their sales by increasing marketing efficiency. They have to do a better job of targeting specific groups -- women, minorities, et cetera," Malesh said.

All of those people "have been car buyers for years" -- but for years, the auto industry has been wedded to a mass-marketing concept that spoke to buyers as if they were a monolith, Malesh said. That practice has hurt domestic car companies among blacks, who for decades have been strong supporters of U.S. automakers.

Blacks have been remarkably loyal customers of the U.S. car industry over the years, considering the way Detroit treated them in the past. And although blacks have increased their purchases of foreign cars in recent years, they have done so at a far slower rate than the country as a whole.

"Domestics have the largest share of black buyers, but that share over the years has remained flat," Malesh explained. In 1989, for example, blacks accounted for 3.2 percent of all new domestic passenger cars sold in the United States. They accounted for 3.3 percent of those sales in 1995, according to Power estimates of minority auto purchases.

The effort to woo minority buyers these days is driven by one color only, said Malesh. Green.

Minority marketing experts such as Jorge Lezcano agree.

"The fact is that you have 26 million Hispanics in the United States, which means that, numerically, you have a larger potential market than you have in Canada," said Lezcano, president of the Miami-based Lezcano Associates Inc., one of the largest Hispanic marketing firms in the country.

Lezcano's company handles Hispanic marketing initiatives for Chevrolet, as well as for a number of other big-name clients, including Pillsbury Co. and Stouffer Foods Corp. Doing Serious Research

Ethnic or diversity marketing -- both of which live under the rubric of "relationship marketing" -- does not mean translating mass-market messages from English to Spanish, Lezcano said. It means doing serious research, finding out what works in one community versus another. It also means paying a lot of attention to differences within a group, Lezcano said.

"People say Hispanics.' But some Hispanics' prefer to be called Latinos,' Lezcano said. Hispanics/Latinos include Cubans, Colombians, Mexicans, Puerto Ricans and others, all of whom may speak the same language, but who have different cultures, he stressed.

The key to addressing cultural differences successfully is to appeal to them without stereotyping the target audience, or alienating the general population, Lezcano and Carridine said.

For example, all of Cadillac's research among blacks "says that we don't want to be singled out or treated differently. It simply says that we want to be included and treated as a real part of America," Carridine said.

To that end, Cadillac is weaving images of black professionals and family life into its advertisements, images similar to those routinely used to portray whites. The idea is to create "a warm and fuzzy feeling" -- one that plays to black cultural nuances such as dress, language and body language, but that has lots of crossover appeal for whites, Carridine said.

General Motors also is running similar ads showing people with disabilities, including one TV ad showing disabled people with the U.S. Olympic Ski Team and a Chevrolet Tahoe sport-utility vehicle. Getting Dealers Involved

GM, along with other car companies, also is stepping up training programs to teach dealerships how to relate better to people from diverse backgrounds. Cadillac last year conducted two such programs for dealers in Philadelphia and the Washington metropolitan area.

"At first, there was some resistance. People didn't want to come, and when they came, they didn't want to be there because we were going to discuss diversity,' " said Carridine. "But when we showed them how being able to work with those different people was good for business, they became enthusiastic," he said. My mother, who died last February, would have appreciated that kind of enthusiasm. "It's such a beautiful car," she used to say of her beloved Coupe DeVille.

But when the DeVille was backed into a church's brick wall by a teenage driver, she dumped the car in favor of buying what was then a new Chevrolet Celebrity and Chevrolet Cavalier. "I could've gotten another Cadillac for what I paid for the both of those," she said, somewhat overstating the case.

But she explained that she just didn't want to go through the hassle of shopping another Cadillac dealer. "Those Chevrolet people," she said. "They're much nicer." CAPTION: Advertisements for 1996 model year cars from recent issues of Ebony magazine include, clockwise from top, Ford's Taurus, Chrysler's Concorde and General Motors's sport utility vehicle, the Jimmy. Under diversity marketing, advertisers try to appeal to target audiences without alienating the general population.