Montgomery County police said yesterday that 17 monkeys seized in a raid on a Silver Spring laboratory two weeks ago were apparently stolen earlier this week from the supposedly secret location where they were being kept.

In a bizarre twist to the controversy over treatment of test animals at the Institute for Behavioral Research, the monkeys were discovered missing sometime Tuesday from the basement of a Rockville home where they had been taken after the Sept. 11 raid.

Embarrassed authorities were unable to explain how the animals had disappeared. "Evidence seized is normally placed under lock and key," said Michelle Kingsley, spokeswoman for state's attorney Andrew Sonner of Montgomery County. "In this case, due to the large number of animals, that wasn't possible."

Kingsley said the animals had been placed in the custody of two state humane officials and that the idea of stationing a police officer on the premises was thought to be unnecessary.

Late yesterday, a woman who was involved in the monkeys' care was jailed on a contempt of court charge based on her failure to appear before the county judge who is handling the matter. Lori Lehner, 23, was arrested by sheriff's deputies at her Rockville home. Deputies continued to search for a second woman involved in the case, while a third appeared in court and the order to bring her in was rescinded.

At a press conference yesterday afternoon at the Institute for Behavorial Research, Dr. Edward Taub, principal investigator at the lab, who had been seeking the return of the monkeys, warned that the missing animals are in danger and "may be killed with the excuse that this was for their own good."

Taub said his fear was based on what he heard from "official sources" that one of the perpetrators of the alleged theft "is an expert on euthanasia."

"I slept here in the laboratory last night to let them in if they were brought home . . . we have received no word as to the whereabouts of the monkeys," Taub added.

According to Taub, the monkeys were used in invaluable experiments to determine the effects of damage to the central nervous system-- research that had resulted in important gains in learning how to enable humans to recover from strokes.

County police raided the lab after receiving reports that the state's animal cruelty law had been violated. There they found monkeys that "were in such physical and mental stress" that the animals appeared to have bitten off their fingers and arms.

Last week a Montgomery County judge ordered that the monkeys be returned to the lab on the condition that police and prosecutors be allowed to "examine, inspect and observe" them while considering possible criminal charges.

The monkeys were not immediately returned, however, and on Tuesday prosecutors went back to court to request that the animals be kept where they were. A hearing on the request was scheduled for yesterday morning.

Prosecutors were set to argue that they needed a written version of the judge's order calling for the return of the monkeys to the lab and that they have evidence to suggest that the animals had been mistreated.

At his press conference, Taub said a $450 reward was being offered for the monkeys' return and criticized the group, People for the Ethical Treatment of Animals, which started the original police investigation.

Taub said that the initial seizure of the monkeys "was part of an orchestrated effort by private parties opposed to any use of animals in scientific research," but Taub and his attorney, Edgar Brenner, stopped short of blaming anyone for the alleged theft of the monkeys.

Alex Pacheco, the 23-year-old college student and chairman of PETA who started the police raid with what he claimed was evidence of poor conditions at the lab, denied that his group had anything to do with the disappearance of the animals.

"I'm sure people who are concerned about their welfare came in and took them," Pacheco said yesterday. "The monkeys have all disappeared, so they'll never have to go back to the laboratory."