More than three years after Congress ordered stepped-up monitoring of sex offenders, only one state has adopted the government's strict new requirements, and some others are weighing whether to ignore the law and just pay a penalty.

So far, Ohio is the lone state to meet the new federal standards. Elsewhere, efforts have been hampered by high costs and legal challenges from the nation's 686,000 registered sex offenders. Advocates worry that the delays are putting public safety at risk.

"This means more of the same _ that we're losing sex offenders when they cross state lines and disappear," said Erin Runnion, who lobbied for the law after her 5-year-old daughter, Samantha, was kidnapped and killed in 2002.

"It's incredibly frustrating. How many children do we have to lose to repeat sex offenders before we start taking these guys seriously?"

The initial deadline for states to comply was in July. Then the deadline was extended to July 2010, although several states have signaled they may still be unable to meet it. States that do not adopt the mandates risk losing millions of dollars in federal grants.

The law was designed to keep closer tabs on sex offenders, including an estimated 100,000 who are not living where they are supposed to be. It would create a national sex offender registry and toughen penalties for those who fail to register.

The president of the National Center for Missing and Exploited Children said states need more money to adopt the law, and he called on Congress to help.

"We understand that there are challenges in becoming compliant, but the greatest challenge is that states are overwhelmed. And they're going to need resources to address this," Ernie Allen said.

Last year, a federal judge in Nevada declared the law unconstitutional because it would subject offenders to additional penalties after they have served their time. The Ohio Supreme Court heard similar arguments last month from more than 26,000 sex offenders who were convicted before the law was signed.

Critics have also complained that juvenile offenders would appear on registries in some states. And because the law requires offenders to register in person, it could unfairly burden people in rural areas who would have far to travel.

In addition to the legal challenges, states are also struggling with the cost, which could climb into the millions of dollars.

"We have states being very laid back, and states where legislators are pulling out their hair trying to comply," said Alisa Klein of the Association for the Treatment of Sexual Abusers. "And there's lots of states waiting for another state to bust a move and say, 'We're not going to comply.'"