Under current law, only DNA from adults convicted of crimes can be placed in the national database, which is used to compare those samples with biological evidence from the scenes of unsolved crimes. As of January, there were about 1.3 million DNA samples in the database, U.S. officials say.

Adding profiles from thousands of adult arrestees and juvenile offenders would greatly expand the DNA system's worth by increasing the number of potential matches, administration officials say. Justice Department officials have discussed potential changes in federal DNA law with key members of Congress and are pushing for legislation this year.

"DNA is to the 21st century what fingerprinting was to the 20th," says Deborah Daniels, assistant U.S. attorney general for justice programs. "The widespread use of DNA evidence is the future of law enforcement in this country."

But critics say adding juvenile and arrestee profiles to the database threatens privacy by expanding the pool of samples beyond adult criminals. Although only digital DNA profiles would be linked to the FBI computer, the blood or saliva samples from which the DNA was drawn would be kept by state labs, they note.

"It's only a matter of time before the government gets its hands on those DNA samples and starts playing around with our genetic codes," says Barry Steinhardt, privacy specialist for the American Civil Liberties Union's national office in New York City. "They say they don't want to do that, but not too long ago they were saying they'd only take DNA profiles from rapists and murderers and now they want juveniles ... We're not just on a slippery slope, we're halfway down it."

DNA system defenders say the actual samples must be retained for quality-control testing and in the event a DNA match is challenged in court. They note that strict privacy laws prevent researchers from using the stored samples for any other purpose. And they note that the U.S. government already stores fingerprints from arrestees in a giant computer system without causing privacy problems.

Privacy advocates aren't convinced. They note that researchers are identifying genetic markers for height, hair color and other features. They suspect that authorities soon will want to search DNA samples for such genetic markers.

DNA, a cellular acid contained in blood, semen and other body fluids and tissues, is an ideal tool for crime solving. Because it contains an individual's unique genetic code, a DNA sample taken from blood, semen or even traces of saliva in a bite mark left on a crime victim can be used to match the perpetrator to the crime.

In 1989, states began to collect DNA from convicted criminals and add the profiles to a computer that could match them to DNA from unsolved crimes. In 1992, the FBI created a system that linked the state databases via a bureau computer in Morgantown, W.Va.

Thirty states already collect DNA profiles from juvenile offenders, who typically range in age from 13 to 17 but can be as young as 8, according to the Coalition for Juvenile Justice, a Washington, D.C., advocacy group. Since January, Virginia also has collected DNA from those accused of murder, rape and other violent felonies. But under U.S. law, only DNA from people convicted of crimes can be put into the FBI system.

The national DNA database has had many successes. As of December, 6,670 DNA samples had been matched to unsolved crimes, the FBI says.

States that take DNA from the widest range of offenders seem to produce the best results. New York has had 830 matches since it began to collect DNA from violent felons in 1996. But 80% were made after 1999, when the state began to require DNA collection from most other felonies.

In Virginia, DNA from 74 crimes, including 12 rapes and nine murders, has been matched to DNA profiles from juvenile offenders during the past 10 years.

"Not all juveniles are going to become adult criminals," says Paul Ferrara, director of Virginia's DNA program. "But for the few who are, the sooner we have them in the system the better."

It is unclear how many new DNA samples would be put into the system if juvenile offenders and adult arrestees are added. In 1996, the last year for which data are available, 567,200 youths were found responsible for crimes by juvenile courts or other authorities. Virginia expects to collect DNA from 8,000 arrestees this year.

The White House is pushing to make DNA a more effective law enforcement tool. Last month, it announced a plan to spend about $1 billion over five years to improve the national database.