Should towns tell kids when it's time to go to home?

When the fire whistle blows every evening at 9, young residents of Rochester, N.H., know they have an hour to get home. Like an estimated 2,000 US cities and towns, Rochester has a juvenile curfew - a restriction critics consider unconstitutional and an interference with parental authority.

Curfews, enforced mainly in summer months, are frequently a community's response to vandalism, loitering, or noise that it perceives as threatening.

But ''a juvenile curfew smacks of totalitarianism because the state is making a presumption that kids are going to do unlawful acts,'' argues Martin Guggenheim, professor of law at New York University. He considers the intent of juvenile curfews as legitimate and lawful but the effect as too broad.

The same judge who a year ago struck down the curfew in Keene, N.H., as too vague recently upheld the town's amended version when seven children and their parents challenged it. US District Judge Shane Devine said the plaintiffs had no claim since none of them had been held in violation. Randall Ment, executive director of the New Hampshire Civil Liberties Union, who represented the plaintiffs, says he plans to appeal the decision on the grounds that his clients are being damaged by the restraint.

Parents testified that a curfew usurps their choice to grant or limit freedoms in the raising of their children. Mr. Ment says curfews deny children the right of freedom of association and due process based on an ''imagined threat.'' He says there are no clear reasons for the restrictions. ''It's fairly clear that the vast majority of antisocial behavior is committed by those least likely to abide by a curfew,'' he adds.

It is this antisocial behavior at which curfews are aimed. Keene requires anyone under 16 to be off the streets between 10 p.m. and 5 a.m. unless accompanied by an adult, in a moving car, or en route to a job, restaurant, library, movie theater, play, dance, sporting event, religious meeting, or school-sponsored activity. Other New Hampshire towns follow a state law givingthem authority to have a 9 p.m. curfew with no ending time and few exceptions.

Although Keene Police Chief Harold A. Becotte says a curfew gives officers ''a little more of a handle'' in questionable circumstances, he says it can be a problem to verify a young person's claim to one of the approved exceptions.

This discretionary aspect of curfews can be particularly ''arbitrary'' in cities, according to Professor Guggenheim. Rochester's city solicitor, Jerry Grossman, says that police in that town of 23,000 ''know the children, know their names.'' But in Detroit, which has had a curfew for four years, young people must carry ''some type of note or proof'' to show the police they have a ''legitimate reason'' to be out, according to Detroit police Sgt. Kenneth Tempest. Detroit's curfew requires anyone under 18 to be off the streets between 10 p.m. and 6 a.m. with an extension until 11 for 16--and 17-year-olds on Friday and Saturday nights.

Rochester's chief of police calls the curfew ''a good tool for parents'' who no longer have to argue with children about why they can't go out. However, Mr. Ment asserts that a blanket ban is ''not justified by the magnitude of the problem.''

Chief Becotte says Keene's curfew is enforced mainly in summer months when there are problems ''more annoying than criminal,'' including young people ''not being respectful to older people.''

Baltimore issues about 18,000 violations a year of its juvenile curfew, which applies to those ages 7 to 16 between 9:00 a.m. and 2:30 p.m. during the school year and to those under 16 from 11 p.m. to 6 a.m. This is extended to midnight on Friday and Saturday.

When a Baltimore youth is encountered after curfew by police, a police officer does some initial questioning, then takes the young person's name, date of birth, home address, and parent's address. As with most juvenile curfews, repeated violations can result in a parent being summoned to court and fined. In Baltimore, a juvenile's employer also may be held liable.

In communities like Detroit, which recently laid off 1,000 police officers, curfews are ''a cheap way of law enforcement,'' according to Guggenheim. He says curfews are justified as ''protecting young people from the harm of being victims of crime,'' but he considers a juvenile's right to walk his dog at night or watch the stars a freedom ''basic to a free society'' which ''can be infringed only by a compelling . . . reason.''