A group of lawyers who represent indigent criminal defendants in the District violated the federal antitrust laws when they went on a two-week strike in 1983 for higher pay, the Federal Trade Commission ruled yesterday.

In its first antitrust action against lawyers, the FTC ruled 3 to 0 that the strike by the D.C. Superior Court Trial Lawyers Association constituted an "illegal boycott" to coerce the city government into raising the fees it pays to lawyers to represent criminal defendants, and it barred the 100-member group from conducting any such actions in the future.

The trial lawyers went on strike in September 1983, protesting that they were being forced to handle too many cases for too little pay. They said their compensation under the city's Criminal Justice Act of $30 an hour for court appearances and $20 for work in their offices had not been raised in 13 years.

After court officials warned that conditions at the court were reaching a "crisis point," Mayor Marion Barry and D.C. Council leaders found $4.1 million in the city budget to raise the lawyers' wages to $35 an hour for work in and out of court. The private lawyers supplement the representation provided by government lawyers who work for the Public Defender Service.

In an opinion by Commissioner Mary L. Azcuenaga, the FTC rejected the group's argument that the strike was not covered by antitrust laws because it was aimed at providing better counsel for the poor.

"Although we do not question the lawyers' genuine concern for their clients, we find unpersuasive the . . . argument that they undertook their coercive course of conduct for altruistic rather than for commercial purposes," the FTC found. "We find instead that the purpose in conducting the boycott was to improve their own economic well-being."

Karen E. Koskoff, a former president of the trial lawyers group who was named in the FTC's suit, called the ruling "outrageous" and said she would appeal. "The FTC laws were made to protect consumers and they are being used to abuse consumers," said Koskoff, who now practices law in Connecticut. "The First Amendment gives me the freedom to petition my government and it gives me the right to assemble and I intend to assert that right . . . . I'm sure some people did it went on strike for money, but I didn't."

The higher rates the lawyers achieved by striking, she said, mean that "now the lawyers who are down there can make an adequate living and they can do it by taking fewer cases. That means each individual person who's represented gets a lot more time . . . . The client's the most important thing and that's who we were trying to help."

The commission's decision yesterday reversed the action of an FTC administrative law judge who dismissed the case. The administrative law judge found that the strike constituted an illegal boycott to raise prices but dismissed it because the strike had no adverse effects, because higher fees were necessary to satisfy the constitutional requirement of effective representation of counsel, and because the strike was the "only feasible way" to secure the increase.