A federal judge has ruled unconstitutional a longstanding Montgomery County jail practice of strip-searching all detainees even when there is no "probable cause" to believe they are concealing weapons or contraband.

U.S. District Court Judge Joseph H. Young in Baltimore, in a case brought by the American Civil Liberties Union, also held that all persons detained on minor charges for 24 hours or less since May 1979 at the county detention center are entitled to seek thousands of dollars in damages against the county.

That may be as many as 5,000 persons, according to Arthur B. Spitzer, National Capital Area ACLU legal director. Montgomery County officials had no specific figures but said the number is much smaller.

"It's substantially under 100, possibly under 20," said County Attorney Paul A. McGuckian.

The ruling by Judge Young follows a similar ruling by the U.S. 4th Circuit Court of Appeals in 1981 throwing out indiscriminate strip-search practices in Arlington County. Both courts held that the practice violates Fourth Amendment protections against unreasonable searches and seizures.

" . . . I just hope that county officials will re-think their policies and not appeal this case," Spitzer said.

McGuckian said he has not had a chance to read Young's 25-page ruling and would not comment.

Most major jurisdictions in the Washington area, including the District of Columbia and suburban Virginia counties, have abandoned indiscriminate strip searches. Only Prince George's County in suburban Maryland continues the practice, says Spitzer, and attorneys there are currently challenging its legality.

Montgomery County stopped its practice in September 1982, following a federal court injunction that was issued after the ACLU filed its lawsuit leading to this week's ruling by Judge Young.

Young, however, dissolved the injunction, which was temporary, holding that the plaintiff who filed the lawsuit, Vivian Anderson Smith, lacked standing to seek a permanent injunction because she is not likely to be arrested and strip-searched again in Montgomery County.

Young warned county officials that "although they are no longer under court order prohibiting them from engaging in an indiscriminate strip-search policy, it would be unwise for them to do so in light of the court's holding" that the policy is unconstitutional.

The case stemmed from Smith's arrest on Nov. 12, 1981, on a contempt-of-court citation for allegedly failing to appear in court in a child support case.

She was taken to the county detention center on Seven Locks Road where she was ordered to remove her clothes and undergo a complete search, including an examination of her hair and all body cavities. The search was conducted in the presence of another female prisoner, according to court records. She was released the next day.

Young held that both the search--done without probable cause to believe Smith was concealing weapons or contraband--and Smith's lack of privacy were unconstitutional.

In addition, Young approved a "class action" for monetary damages against the county by all "temporary detainees" held for 24 hours or less at the detention center since May 1979. He ordered the county to notify members of the "class" so they can begin seeking damages. Smith is seeking $150,000 in damages.

The May 1979 cutoff was determined by the three-year statute of limitations from the date the ACLU lawsuit was filed in May 1982.