A federal judge has ordered that paid advertisements run in 16 East Coast newspapers starting tomorrow to help attorneys in a class action lawsuit locate what they say may be thousands of black people who were discouraged from joining Holiday Spas.

The unusual action comes as lawyers for the plaintiffs and for the chain of popular health and exercise centers prepare for trial in February on the discrimination allegations.

U.S. District Judge Joseph C. Howard in Baltimore ordered the newspaper notices in an effort to identify black people from Atlanta to Boston who think that they were discouraged from joining any of the fitness organization's 40 spas or were steered to predominantly black spas in the last five years.

Attorneys for the spas rushed to court yesterday in a last-minute effort to block a planned news conference by the plaintiffs today to announce details of the advertising campaign. Howard refused to block the news conference.

The Washington Lawyers' Committee for Civil Rights Under Law, which is spearheading the lawsuit, said it is difficult to estimate how many people may have been affected by the alleged discrimination. But Rod Boggs, committee executive director, put the number at "multiple thousands."

Howard ordered the advertisements to appear in daily and weekly newspapers in Washington, Baltimore, Philadelphia, Boston and Atlanta, where the spas are concentrated.

The daily papers include The Washington Post, Baltimore Sun, Philadelphia Inquirer, Atlanta Journal-Constitution and Boston Globe. The list also includes several black-oriented newspapers, including the Afro-American papers in Washington and Baltimore.

The papers have a combined circulation of almost 4 million.

In the lawsuit, the plaintiffs contend they suffered a pattern of discrimination at dozens of spas. At some, they said, black potential customers were recorded in sales books with codes such as "DNWAM," meaning "Do Not Want as Member." In other cases, they said, blacks were given cursory tours, quoted unusually high membership fees or steered to predominantly black fitness centers.

Spa owners have denied the allegations.

The suit, filed last November in the District, was moved to the federal court in Baltimore several months ago, in part because the companies that own the spas have their headquarters in Maryland.

The companies are U.S. Health Inc. and Holiday Universal Inc. of Towson. The fitness centers they operate are known variously as Holiday Spas, Holiday Espre Centers, Holiday Health and Racket Centers and Holiday Supreme Spas.

The advertisements include a "notice of intent to file a claim" that can be filled out by black people who believe they may qualify as members of the class action suit. The ads also provide a "request for exclusion" for blacks who wish to drop out of the suit.

The suit seeks unspecified monetary damages. Boggs said law firms in the five cities have mailed notices to 2,000 people who have been identified as potential class-action members, "and we expect many more to respond to the advertisements."

He said the ads will cost $30,000 to $40,000, with the plaintiffs paying the bulk.

In attempting to block today's planned news conference, spa lawyers called it a "veiled attempt by plaintiffs to circumvent" the carefully structured wording of the advertisement approved by the judge.

"Obviously, you can look at it as free publicity," spa lawyer Richard T. Sampson said. Attorneys for the plaintiffs said the ad is complex and legalistic, and a news conference is a legitimate way to explain it.