No child in recent memory has been snatched from the streets of Tullytown and molested. No known sex offenders live there. And none is about to move in.

What has come instead to this Bucks County, Pa., borough of 2,000 is a national epidemic of jitters.

In September, its Borough Council passed an ordinance barring anyone convicted of a sex crime from taking up residence within 2,500 feet, or nearly a half-mile, of any school, park, playground or child care center. When the circles were drawn, nearly all of 2.1-square-mile Tullytown was off-limits.

"I'd rather have us do something now," said council member Beth Pirolli, "than wait until there's a tragedy."

Tullytown's ordinance is thought to be the first of at least seven in Pennsylvania -- most of them passed in quick order by nearby communities in Bucks.

They have plenty of company countrywide. Scores of chiefly suburban towns and townships are carving out sex-offender-free zones faster than they can be counted. Just since late spring, about three dozen in New Jersey have moved to throw up the barricades around places where children gather, from bus stops to beaches.

State versions also have been passed by 16 legislatures, mostly in the Midwest, but including California and Florida.

The frenzy has been fed by an intensely reported handful of fatal child abductions in the past couple of years, and by the growing consensus that community-notification systems -- the Megan's Laws passed by Congress and the states in the past decade -- are scant protection against predators.

Experts generally contend that the local ordinances will not do much good, either, and could do harm by giving the public a false sense of safety. They predict that efforts to rehabilitate offenders will be set back, and that ghettos of sex criminals will emerge, mostly in cities. That is assuming the exclusion zones withstand constitutional challenges, which have already begun.

Nonetheless, "every town council is getting the idea that this is the thing for them to do," said Ronald K. Chen, a Rutgers University Law School dean and specialist on Megan's Laws. Each is "trying to make it someone else's problem, but that's not a logically consistent way to address the issue. I mean, they've got to live somewhere."

In the offender-free movement, that is anywhere but here.

Those who break the laws can face fines and jail time. Typical is the maximum penalty in Doylestown Township, Bucks County: $1,000 and 90 days.

In New Jersey, which has 10,700 registered sex offenders, the first zones were created in May by Hamilton Township, Mercer County. It was there in July 1994 that 7-year-old Megan Kanka was raped and killed by a neighbor who had twice been convicted of sexually assaulting children.

In the past five months, Jersey towns have yanked in the welcome mat, or proposed to, at a rate exceeding one a week.

The idea took hold in Pennsylvania, where 7,500 offenders are registered, and spread in characteristic domino fashion.

Moses Scott, a Tullytown father of two young children, agreed with critics that "restricting [sex offenders] live is not doing anything." But until someone finds a cure for pedophilia, he added, the zones "might be the best solution."

Usually the restrictions are only on residency, and offenders already living in the zones can stay. But some communities have cracked down harder. Binghamton, N.Y., passed one of the most stringent ordinances, in effect barring offenders from walking or driving on most streets; it is on hold pending a court challenge.

More often than not, said Chen of Rutgers, "the exclusion is so comprehensive that if it doesn't prevent offenders from having any meaningful existence in the town, it comes pretty close."

Chen is among the increasing number of critics as the trend toward offender-free zones spreads. Almost without exception, experts in psychology, law and law enforcement lambaste it.

The value in passing exclusion ordinances "is to make politicians feel better about themselves because it does nothing to protect the public," said John Furlong, a Trenton, N.J., lawyer and coeditor of A Megan's Law Sourcebook. "It makes about as much sense as banning a Muslim extremist with ties to al Qaeda from living within 2,500 feet of an airport. Would that make you feel any safer flying?"

The ordinances, Furlong said, overlook the chief victimizers of children: relatives and acquaintances. Each year, there are 60,000 to 70,000 arrests on charges of child sexual assault, according to the U.S. Justice Department, but only about 115 abductions by strangers.

Critics argue that offender-free zones go beyond being a harmless fad. They predict that the restrictions will drive many offenders underground, making the states' task of keeping tabs on a national population of 500,000 even more difficult.

"What they're probably going to do is move into a community -- and not register," said Carolyn Atwell-Davis, legislative director for the nonprofit National Center for Missing and Exploited Children. "It's better to know where they are than where they aren't."

Lt. Janet McNeal, commander of the Megan's Law unit for the Pennsylvania State Police, worries that "these ordinances will hinder offenders' ability to maintain stable lives" by cutting them off from decent housing, social contacts and jobs.

A 2001 study by Virginia's Criminal Sentencing Commission found employment to be a big factor in whether sex offenders relapsed: the steadier the work, the lower the recidivism.

Courts have forced Megan's Laws to distinguish between low-risk offenders and violent predators. New Jersey, for instance, has three categories and an extensive review system to classify its sex offenders.

At center stage is the Iowa law that set up exclusion zones throughout that state. It was struck down last year by a federal judge who ruled that the zones denied offenders due process and punished them again for the same crime. That decision was overturned on appeal.

In late September, the Iowa Civil Liberties Union asked the Supreme Court to hear the case.

Restricting where offenders may live is cruel and unusual punishment, prohibited by the Eighth Amendment, said Larry Frankel, legislative director of the Pennsylvania American Civil Liberties Union.

"Once you've served your time, you have the right for the state to stop punishing you," he said.

His own children grown, Robert Pritchard, 52, fears for the youngsters who ride their scooters around Tullytown, where he lives and works.

He said of offenders: "I understand they have rights. But this is a small town, and they don't belong in this community. What about the children's rights?"