A civil rights group filed a federal racial discrimination lawsuit yesterday against Diamond Cab Co. of D.C., alleging that the firm's dispatchers routinely fail to provide cabs for black Southeast Washington residents calling for service.

The class-action lawsuit, brought by The Equal Rights Center and two black Southeast Washington residents, came after a series of test calls last year to Diamond's dispatchers showed a huge gap in response between predominantly white areas in Northwest and predominantly black areas in Southeast, civil rights advocates said.

David Berenbaum, executive director of the center, said the lawsuit is unique because it involves allegations about company-controlled dispatching, rather than the practices of individual drivers on the streets. For years, black D.C. residents have complained about their difficulties in hailing cabs at curbside, particularly at night.

"Here we have a record based on testing the company directly," Berenbaum said. "This is not an issue of driver availability. Here we have a dispatcher making a decision as a company representative that intentionally discriminates in the marketplace."

Diamond, the oldest cab company in the District, says in the Yellow Pages that it offers 24-hour, radio-dispatched service to "DC & the entire Metro area." With 295 cabs, Diamond is one of the city's largest providers of dispatched service.

Yesterday, Philip Lebet, Diamond's acting chief dispatcher, said the company does not discriminate against anyone and expressed surprise at the allegations.

"Nobody told us we're being sued, and we're not aware there's any problems," Lebet said. "Do we engage in that kind of conduct? Of course not. That's against the law."

Lebet said people throughout Washington have to wait longer for cabs these days because of a shortage of drivers and increased demand. But he said those problems extend to all parts of the District, not just the Southeast quadrant.

The lawsuit, filed in U.S. District Court, accuses Diamond Cab of violating the federal Civil Rights Act and local laws. Federal civil rights laws cover the actions of private businesses that offer services to the public; in this case, Diamond is accused of refusing to serve people because of their race. The D.C. code calls for taxicab companies to provide service to all people and to all parts of the city, and the D.C. Human Rights Act also bars companies from engaging in discrimination.

The suit seeks an unspecified amount of money in damages and a court order requiring Diamond Cab to provide equal service to all parts of the city.

The tests were done by volunteers who called Diamond's taxi dispatchers at roughly the same time from locations in Northwest and Southeast. According to the lawsuit, all 14 requests for service in Northwest resulted in Diamond cabs. But in Southeast, the lawsuit said, only one cab showed up in 14 attempts. According to the lawsuit, "the results of the study demonstrate an unmistakable and egregious pattern of racial discrimination, as well as discrimination on the basis of residence."

In many cases, callers in Southeast were promised cabs but none showed up, the lawsuit said. In others, Diamond's dispatchers said no cabs were available, referred callers to other companies or simply hung up, the lawsuit alleged.

Berenbaum said tests of other D.C. cab companies turned up indications of similar problems. For example, he said Yellow Cab Co. of D.C. showed up nine of 11 times in neighborhoods in Northwest, but three of 11 times in Southeast. By contrast, Capitol Cab Cooperative Association Inc. responded to seven of nine calls from Southeast, he said, but appeared only five of 12 times in Northwest.

The Equal Rights Center is pursuing an industry-wide investigation, and further legal action is possible, Berenbaum said.

Vaughn Williams, president of Yellow Cab Co., said that his dispatchers try to serve callers in Southeast but that they cannot control the actions of drivers, who own their own cabs. Despite company policy, "many drivers don't want to work Southeast," and they roam in Northwest instead, Williams said.

"If there are no drivers in Southeast, we can call a job until we're blue in the face, but nobody is there," said Williams, adding that he would be willing to work with The Equal Rights Center and others to find a solution to the problem.

In the action against Diamond, the two named plaintiffs are Lamont Mitchell, a special assistant to Mayor Anthony A. Williams for East of the River Neighborhood Revitalization, and Viola Bowen, a retired Navy employee. Berenbaum said other named plaintiffs will likely be added as more complaints are reviewed.

"I think the taxicab industry is the last bastion of segregated life in Washington," said Mitchell, 44. "You can go and buy a $200,000 or $300,000 home, go to Howard University or Georgetown, but you can't catch a cab ride home."

Mitchell, whose job calls upon him to promote development in Southeast Washington, said he has called Diamond's dispatchers repeatedly over the years, only to get the same response. "They promise you they're going to come, and they don't come," he said.

Bowen, 82, said she waited in vain for 90 minutes last month after calling a Diamond dispatcher for a taxi to take her from her home on Alabama Avenue SE to a downtown department store, where she wanted to buy a white dress for her granddaughter to wear at a high school graduation ceremony. She finally gave up, she said, and wound up giving her granddaughter money so that the teenager could buy the dress herself.

"If you have a doctor's appointment, or some other place you want to go, it's very stressful when they don't show," Bowen said. "It's not a good feeling."

Taxi companies frequently have been accused of racial discrimination in the District and other major cities. Phil Pannell, a Southeast Washington community activist who leads the Ward 8 Democrats, said he hoped the lawsuit would change the way Diamond and other cab companies in Washington do business. Pannell, who is not part of the suit, said, "I can now see why we don't see Diamond cabs in Ward 8 that often. I've had problems myself."

The Equal Rights Center, a nonprofit civil rights group formed last year, crafted the lawsuit with pro bono assistance from the law firm of Crowell & Moring and the Washington Lawyers Committee for Civil Rights and Urban Affairs. The lawyers committee pursued a discrimination suit against other taxicab companies in Washington a decade ago.

"Think how many people have missed airplanes or trains or appointments because of this," said Roderic V.O. Boggs, executive director of the lawyers committee. "In most of these cases, they say they will come, and they don't do it."