New Jersey's pioneering Megan's Law, which costs millions of dollars to alert citizens when sex offenders move nearby, may not make children safer, new research suggests.

A federally funded study under way in Trenton is trying to determine whether Megan's Law is worth the cost of its "enormously expensive" monitoring and enforcement requirements, said Phillip Witt, a consultant on the study.

A declining trend of sex attacks on children began before the law took effect and has continued, raising the suggestion that New Jersey's Megan's Law - one of the first laws of its kind in the nation - may not have influenced the trend, researchers say.

"We don't know whether Megan's Law really works," said Witt, who helped create the risk-assessment system used by New Jersey's courts to classify sex offenders.

"Just a few studies have looked at whether community notification laws are effective," he said. "I believe they have very little effect."

The 1994 law is named after Megan Kanka, a suburban Trenton girl who was raped and murdered by a convicted sex offender living across the street. It has been a model for dozens of state laws across the country.

The law requires sex criminals to report their whereabouts to law enforcement authorities, who must maintain a catalog of the offenders and notify residents when a high-risk offender moves nearby. The tracking and notification apparatus in New Jersey costs county and local governments millions of dollars.

The $38,252 study by the state Department of Corrections appears to be one of the nation's first attempts to analyze whether Megan's Laws make children safer from sex criminals. The study, funded by the National Institute of Justice, the Justice Department's research branch, is expected to be finished early next year.

One phase has ended. It charted sex offenses against children in the decade before 1994 and in the decade after. Researchers said they were surprised to find that a steady decline in sex crimes across New Jersey had begun in 1991 - three years before Megan's Law.

Sex offenses against children have also declined since Megan's Law was enacted, but there has been no way to know whether that's because of the law.

"Sex-offender rates are down, and we can't attribute it to Megan's Law," said Kristen Zgoba, a Corrections Department researcher leading the study. "Is it worth the amount of money and manpower we're pouring into it?"

Nationally, sex offenses against children fell 49 percent between 1990 and 2004, according to the Crimes Against Children Research Center at the University of New Hampshire. Meanwhile, the broad category of violent crime in the United States also plunged, according to government figures.

"Something obviously changed that needs to be explained," said Lisa Jones of the Crimes Against Children Research Center.

Any number of factors could have led to the declines, Jones said. She cited economic prosperity during the 1990s; increased numbers of police, social workers and offenders in jail; and widespread introduction of antidepressant drugs in the late 1980s.

The decline in sex offenses has led some researchers to question whether Megan's Law has had any impact, and whether its enormous cost can be justified.

In the year after its adoption, only in Ocean County did sex crimes fall significantly, "but we don't know if that was due to Megan's Law," Zgoba said.

Sex offenses against children statewide rose slightly in 1998 and 1999, but resumed their decline in subsequent years.

"Megan's Law is riding the coattails of the natural downward trend," Zgoba said.

Megan's mother, Maureen Kanka, who campaigned for the law, said she believed it would withstand the study's scrutiny.

"Is the law perfect? No. Does it make a difference? Absolutely," she said.

"If I had known there was a pedophile living across the street, Megan would be alive and well today," she said. "I know the effectiveness of the law because I get e-mails about it all the time."

Trenton enacted Megan's Law amid the outrage that followed the murder. Two years later, Congress passed a federal version.

Lawmakers reasoned that if parents could take steps to keep their children away from pedophiles, convicted sex offenders would be less likely to commit new offenses.

New Jersey is home to about 11,300 registered sex offenders, according to state police records. About 2,190 are regarded as high risk. Their pictures and addresses appear on the New Jersey State Police Sex Offender Registry Web site. Local authorities are supposed to have notified people living near them.

To maintain the Internet registry, state police employ seven full-time civilians who earn between $35,000 and $52,000 a year, excluding benefits, according to state records.

Though the state orders local governments to monitor offenders' whereabouts and notify communities when a high-risk offender moves nearby, local and county taxpayers foot the bill, Assistant State Attorney General Jessica Oppenheim said.

Routine door-to-door notifications can cost thousands of dollars. Police in Voorhees, for example, said they had expected to spend about $3,000 to alert people in the sparsely populated Ashland development that a high-risk sex offender had moved in. The offender moved again before police started the notification.

The bill for the police notification would have soared higher had the sex offender's neighbors included people in a high-rise apartment complex, police said.

Most of the costs of monitoring sex offenders fall to the 21 county prosecutors' offices across the state.

Camden County, with 256 high-risk sex offenders, spends about $232,000 a year in salaries and benefits to administer Megan's Law, according to the Prosecutor's Office.

Essex County, home to 341 high-risk offenders, spends more than $1 million a year, said Paul Loriquet, spokesman for the Prosecutor's Office.

One of the remaining phases of the Megan's Law study will try to calculate the statewide costs.

"There's no question there's a substantial price tag," said State Sen. Peter Inverso, a Republican representing parts of Mercer and Middlesex Counties who sponsored Megan's Law. He also sponsored another bill that passed in March requiring a study of whether Megan's Law is being implemented consistently across the state.

"It's hard to prove that children are safer," Inverso said. "But I firmly believe there's been a benefit, although there's been no empirical evidence to support it on either side."

Contact staff writer Sam Wood

at 856-779-3838 or samwood@phillynews.com.