San Francisco ? \In a startling new survey, a child advocacy group found that states across the country have lost track of tens of thousands of rapists, child molesters and other sex offenders who are supposed to be registered in Megan’s Law databases.

Prompted by an Associated Press investigation that revealed California had lost track of at least 33,000 sex offenders, Parents for Megan’s Law contacted all 50 states by telephone to ask about the accuracy of their registries.

It found that states on average were unable to account for 24 percent of sex offenders supposed to be in the databases. And 18 states, including Texas and New York, plus the District of Columbia said they were unable to track how many sex offenders were failing to register or simply did not know.

Federal law requires the addresses of convicted sex offenders to be verified at least once a year.

But the survey found that up-to-date addresses for more than 77,000 sex offenders are missing from the databases of 32 states. And in the other 18 states and the District of Columbia, which are responsible for 133,705 offenders, thousands of the ex-convicts may have disappeared.

“They’re implementing Megan’s Law, then turning their backs on it,” said Laura Ahearn, executive director of the nonprofit agency in New York. “They need the technology and the staff to track down their sex offenders.”

All states responded to the group’s survey, but only 32 were able to provide failure rates. Many of these said they had never audited their sex offender registries and provided only rough estimates of their accuracy.

The survey, which the group plans to release today, relied on the word of officials in each state.

The survey said Oklahoma and Tennessee had the highest rates of noncompliance, both at 50 percent. A Tennessee official disputed this, and Oklahoma’s Corrections Department spokesman, Brian Johnson, said the figure was just his best guess.

The databases are supposed to help the public and police monitor sex offenders by keeping track of their home and work addresses and other personal details. Adults can search the database at sheriffs’ offices or police departments, assuming the information is kept up to date as required.

All states have versions of the law named for 7-year-old Megan Kanka, a New Jersey girl who was raped and killed by a child molester who had moved in across the street.