ATLANTA, NOV. 20 -- Officials here imposed the city's strictest curfew since the child murders of the early 1980s, threatening to jail parents of youngsters caught on the street after hours.

Three children were caught violating the curfew, which went into effect at 11 p.m. Monday, police said today. Two youths were picked up by their parents from police stations. The third, a 12-year-old girl, was taken home after her parents refused to pick her up, and the parents were issued a warning, said Deputy Chief W.J. Taylor.

The American Civil Liberties Union has threatened to challenge the law, but city officials say it is needed to help reduce the highest rate of serious crime in the nation. Mayor Maynard Jackson praised the curfew, adopted earlier this month by the City Council on a 13 to 1 vote, as an excellent way of keeping youngsters from being used as drug runners or lookouts.

The measure requires persons under 17 to be off the street between 11 p.m. and 6 a.m. weeknights and between midnight and 6 a.m. on weekends, unless participating in school activities, returning from work or accompanied by an adult. Parents of repeat offenders could be fined or jailed.

The curfew is similar to one adopted at the height of a series of 29 slayings of young blacks in metropolitan Atlanta in the early 1980s. The original curfew applied to children 15 or younger and did not penalize their parents.