A federal judge, in a sharply critical decision, has ruled that District of Columbia police routinely detain thousands of criminal suspects for unconstitutionally long periods of time before bringing them before a judge.

The ruling sets the stage for what likely will be a major revamping of the way in which city police officials deal with suspects during the first hours or days after they are arrested. It also raised the possibility of a shift to longer hours for the D.C. Superior Court system to permit speedier presentments and arraignments. Some officials, however, expressed doubt yesterday that a major change in court procedures would take place.

Judge William B. Bryant, chief judge of the U.S. District Court here, declared in the ruling made public yesterday that the police department "has simply not taken seriously the urgency of the Fourth Amendment command that an arrested individual be brought promptly before a magistrate for a determination of probable cause."

Bryant ordered the department to propose a method of eliminating what he termed "the long, unnecessary and unconstitutional delays the court has found layered throughout the detention period prior presentment.

Any court-ordered revision in police procedures would apparently be based, at least in part, on the department's proposals.

More than 60 per cent of those arrested by city police in a recent four week period were detained for more than a full day before they were presented in court, according to lawyers for the American Civil Liberties Union Fund of the National Capital Area. The ACLU Fund brought the suit on which Bryant issued his ruling.

The ACLU's statistics, the lawyers said, were based on data supplied by the Police Department for March and April of last year.

In contrast, Bryant said in his ruling that "the average time to process and arrestee should normally take no longer than 1 1/2 hours." Bryant left unclear, however, how rapidly the police must bring suspects before a judge to comply with the Fourth Amendment prohibition against "unreasonable searches and seizures."

"The Police Department," Bryant said, "has argued that the delay in presenting arrestees is 'reasonable' when one considers the other administrative and enforcement matters the police must handle each day.

"What defendants have failed to conside," he added, "are the important liberty interests of the individual at steke in any pre-presentment detention. The individual is restricted in his physical movement and his ability to go to work or carry on his life. His reputation may be impugned even during a short detention. The interests of the police are not as significant during this post-arrest detention period."

Robert L. Chenikoff, and assistant D.C. corporation counsel who represented the city in the suit, said last night the city has not decided whether to appeal Bryant's ruling. But he added that the District government would revise its procedures for dealing with newly arrested suspects.

'The District has to take a hard look at what it does, and I'm sure we can do better," Chernikoff said. "That which we can improve we will improve."

He said the opening this week of a new headquarters building for the D.C. Superior Court may lead to speedier handling of criminal suspects.

Ralph J. Temple, the Washington area ACLU's legal director, and Bruce D. Sokler, a lawyer for Covington & Burling who acted aa a volunteer ACLU attorney in the case, described Bryant's ruling as significant for number of reasons.

They said it reaffirms fundamental constitutional protection. They noted that persons detained overnight or longer by the police often lose a day's wages, or even their jobs. They argued that long periods fof detention sometimes lead to "friction" between the police and criminal suspects and to possible "police abuses." Prolonged detention, they added, denies suspects their rights to prompt release on bond or personal recognizance. Moreover some suspects, they said, have all charges against them dropped as soon as they appear before a judge and, therefore, ought not to have been detained at all.