Police cannot enforce a law barring sex offenders from working with children, Tuesday's meeting of the Knesset Committee on the Rights of the Child revealed.

The 2001 law bars the employment of sex offenders at any institution that works with minors or the developmentally impaired. But from 2001 to June 2007, the committee learned, police opened only four investigations into the employment of sex offenders at schools, daycare centers and other places that work with children, and none resulted in an indictment.

Every year, some 780 Israelis are convicted of sex crimes. About 200 are sentenced to jail and another 200 to community service, the Public Security Ministry said. Ten to 15 percent of these people commit another sexual offense within five years of their conviction.

Aryeh Mor, who heads the Education Ministry's security department, told the committee a directive was sent to all educational institutes detailing the law's requirements. In particular, he said, they were told that every student teacher must obtain authorization from the police that he is not a sex offender, and schools must check these authorizations. The directive also applied to summer camps, he said, while youth movements and local authorities have issued similar instructions.

The police set up a computerized system to issue the authorizations. But between 2001 and June 2007, only two of the 67,500 people who sought permits were rejected.

Superintendent Meir Berkovich told the MKs that police cannot spare time from their many other urgent tasks to actively seek out employers who violate the law, so they investigate only on tips.

Mor said that as far as the ministry knows, not a single institution has thus far failed to demand the requisite authorizations. But committee chairman Zevulun Orlev (Habayit Hayehudi ) was not reassured.

"If you haven't found even one case of an institution failing to perform such a check of its employees, that raises questions," he said. "There's no such thing as perfection. So if you haven't found even a single violator, that means your supervision is flawed."

He also criticized the police, saying, "If only four cases were opened, and not a single indictment filed, during the law's seven and a half years of existence, then something is very wrong with the supervision and enforcement system."

Attorney Meira Bassok of the Na'amat women's organization cited another problem: Community centers, she said, are not covered by the Education Ministry's directive, and many are not aware that they have to obtain police authorization for their employees.

Orlev also complained about the lack of a system to warn institutions if an employee commits a sex offense after being hired. He proposed police set up a system to automatically cross-check their database of offenders with their database of people who received permits to work with children.

One recent high-profile case in which a convicted sex offender was found to be working with minors despite the law occurred in April, when Yosef Nunu - a man convicted of both murder and multiple sex offenses against minors - was arrested for indecent assault against a suicidal 17-year-old he had been hired to care for at Meir Hospital in Kfar Sava. He was hired by Matav, an organization that provides caregivers for patients who need round-the-clock care. The organization subsequently claimed that by law, it is forbidden to ask its employees for a good-conduct certificate from the police, and therefore did not know about Nunu's criminal past.

Ofra Edelman contributed to this report.