Slowly, and largely under the radar, a growing number of local law enforcement agencies across the country have moved into what had previously been the domain of the FBI and state crime labs — amassing their own DNA databases of potential suspects, some collected with the donors’ knowledge, and some without it.

And that trend — coming at a time of heightened privacy concerns after recent revelations of secret federal surveillance of telephone calls and Internet traffic — is expected to accelerate after the Supreme Court’s recent decision upholding a Maryland statute allowing the authorities to collect DNA samples from people arrested for serious crimes.

These local databases operate under their own rules, providing the police much more leeway than state and federal regulations. And the police sometimes collect samples from far more than those convicted of or arrested for serious offenses — in some cases, innocent victims of crimes who do not necessarily realize that their DNA will be saved for future searches.

New York City has amassed a database with the profiles of 11,000 crime suspects. In Orange County, Calif., the district attorney’s office has 90,000 profiles, many obtained from low-level defendants who give DNA as part of a plea bargain or in return for having the charges against them dropped. In Central Florida, several law enforcement agencies have pooled their DNA databases. A Baltimore database contains DNA from more than 3,000 homicide victims.

These law enforcement agencies are no longer content to rely solely on the highly regulated network of state and federal DNA databases, which have been more than two decades in the making and represent one of the most significant developments in the history of law enforcement.

The reasons vary. Some police chiefs are frustrated with the time it can take for state crime labs to test evidence. Others want to compile DNA profiles from suspects or low-level offenders long before their DNA might be captured by the state or national databases.

The rise in these local databases has aroused concerns among some critics, worried about both the lax rules governing them and the privacy issues they raise.

“We have been warning law enforcement that when public attention began to focus on these rogue, unregulated databases, people would be disturbed,” said Barry Scheck, a co-director of the Innocence Project, which seeks to exonerate wrongfully convicted prisoners. “Law enforcement has just gone ahead and started collecting DNA samples from suspects in an unregulated fashion.”

For their part, law enforcement officials say the crime-solving benefits of local databases are dramatic.

“Our take is that it’s good for law enforcement and good for the community,” said Doug Muldoon, police chief of Palm Bay, a city of about 100,000 in Florida.

In some jurisdictions, it is not only suspects whose DNA goes into the database, but occasionally victims, too.

“If an officer goes to your house on a burglary, they will swab a door handle and then they will ask, ‘Can we get a sample from the homeowner so we can eliminate them as the source?’” Muldoon said. “They say, ‘Sure.’”

The homeowner’s sample goes into the database, too, Muldoon said.

“That’s so profoundly disturbing — that you would give DNA to the police to clear yourself and then once cleared, the police use it to investigate you for other crimes, and retain it indefinitely,” said StephenMercer, the chief attorney of the forensics division of the Maryland public defender’s office.