All states must register sex offenders.

A state idea--requiring convicted sex offenders to register with local law enforcement agencies--has showed up as a mandate in the new federal crime bill.

Although 40 states already have such programs, the bill mandates the requirement with a threat to hold back 10 percent of federal grant money for fighting crime if states don't comply.

Details of the federal requirement and how states are to mesh it with privacy statutes are still up in the air. The bill, signed by President Clinton in September, specifies that people who commit sexual offenses or crimes against children be registered with local police or sheriffs' departments for 10 years, with any changes of address reported. Criminals deemed to be "sexually violent predators" are required to register for life and verify their addresses quarterly. States also are required to establish a system to notify law enforcement officials about the presence of convicted sexually violent predators who have been released from prison.

The U.S. attorney general will establish guidelines for the states, which will have three years to implement registration.

Most state laws require courts or corrections officials to inform prisoners of registration requirements just before they are released from jail. Many states require officials to obtain the anticipated new addresses of those convicted of sexual offenses and forward them to law enforcement agencies. The laws usually require offenders to report each time they move. Registration information can include statements, photographs, fingerprints, employers' addresses, Social Security numbers and aliases.

Louisiana and Washington are two of the states that make information on sex criminals' locations available to the public. Most states, however, keep the information confidential, releasing it only to law enforcement personnel.

California has the oldest registration program in the United States. Since 1947, state law has required that people convicted of certain sex offenses register their whereabouts after release from jail. Offenders found to have mental problems or people convicted in another state also are required to register. California statutes were recently revised to require offenders to give blood and saliva samples at the time of registration for potential DNA identification. Virginia also has a very broad DNA registry requirement for felons.

In Nevada, not only are sex offenders required to register, but so is anyone convicted of a felony in any state who has been imprisoned a year or more. Alabama requires that anyone "convicted of a felony more than twice" register. Penalties for failure to register include prison terms and fines.

Do these programs work? A 1988 California study estimated that 72 percent of convicted sex offenders complied with registration requirements. In the state of Washington, studies found 70 percent of juvenile sex offenders and 76 percent of adults had registered by November 1991.

A California study on recidivism that looked at sex offenders over a 15-year period found that nearly half were re-arrested--20 percent for a subsequent sex offense--between 1973 and 1988. Offenders whose initial arrests were for forcible rape had the highest recidivism rate, with 64 percent charged with some type of offense and 25 percent for a subsequent sex offense.

The California studies also found that most law enforcement agencies believed that the registration process aided in the apprehension of suspected sex offenders.