Law enforcement officials are vastly expanding their collection of DNA to include millions more people who have been arrested or detained but not yet convicted. The move, intended to help solve more crimes, is raising concerns about the privacy of petty offenders and people who are presumed innocent.

Until now, the federal government genetically tracked only convicts. But starting this month, the Federal Bureau of Investigation will join 15 states that collect DNA samples from those awaiting trial and will collect DNA from detained immigrants — the vanguard of a growing class of genetic registrants.

The F.B.I., with a DNA database of 6.7 million profiles, expects to accelerate its growth rate from 80,000 new entries a year to 1.2 million by 2012 — a 15-fold increase. F.B.I. officials say they expect DNA processing backlogs — which now stand at more than 500,000 cases — to increase.

Law enforcement officials say that expanding the DNA databanks to include legally innocent people will help solve more violent crimes. They point out that DNA has helped convict thousands of criminals and has exonerated more than 200 wrongfully convicted people.