By Lawrence Hurley

WASHINGTON, Feb 26 (Reuters) - In a case that spotlights the growing use of genetic data by law enforcement agencies, the U.S. Supreme Court wrestled on Tuesday with the question of when a DNA sample may be taken from a suspect.

The nine justices peppered lawyers for both sides with tough questions during oral argument as they sought to determine what kind of limits should be put on the right of the government to take samples.

Police and prosecutors in Maryland suffered a major setback when the state's Court of Appeals ruled in April 2012 that Alonzo King's Fourth Amendment right to be free from unreasonable search and seizure was violated when he was required to provide his DNA upon being arrested.

Under Maryland law, samples can be taken from anyone arrested for a serious offense without police needing to get a warrant first. Police can then submit those samples to a national database to see if the suspect is linked with any other crimes.

The case argued on Tuesday focuses purely on samples taken without a warrant after a suspect is arrested and charged with a crime, but not convicted of it. Samples taken from convicted felons are routinely submitted to the national database. That practice is not an issue in the case.

The sample King gave after a 2009 arrest in Wicomico County on two assault charges linked him to a 2003 rape. He was sentenced to life in prison after being convicted of the rape and was convicted of one count of misdemeanor assault on the 2009 charges.

His lawyers argue that the sample taken in the assault arrest should not have been used to link him to the rape.

DIVIDED COURT

During the argument, Justice Samuel Alito, a former U.S. attorney, gave the most strident support for the government's right to take DNA.

"I think this is the most important criminal procedure case this court has heard for decades," he said.

What is at stake is "lots of murders, lots of rapes that can be solved using this new technology," he added.

Alito, along with several other justices sympathetic to law enforcement, signaled that he did not think the act of taking DNA samples is any more intrusive than taking fingerprints.

In the same vein, Justice Stephen Breyer said DNA sampling is "no more intrusive" and "much more accurate" than fingerprinting.

As for the question of privacy, Justice Anthony Kennedy, the court's regular swing vote, asked several questions that seemed to indicate that he feels people have a diminished expectation of privacy upon arrest, which might make the taking of DNA samples less of a legal problem under the Fourth Amendment.

He compared the act of taking DNA samples - in which a swab is rubbed on the inside of the cheek - with a police officer "turning someone's pockets out" upon arrest, which is a routine practice.

The justices that appeared most concerned about the government's use of DNA came from opposite ends of the ideological spectrum: the conservative Antonin Scalia and liberal Elena Kagan.

"Just because you have been arrested, it doesn't mean you lose privacy expectations," Kagan said.

Scalia, meanwhile, noted that although it is "a good thing" that DNA can be used to solve crimes, "the Fourth Amendment sometimes gets in the way."

WEEKS TO ANALYZE

Chief Justice John Roberts focused on a potential problem the justices face in deciding the case.

He asked several questions of Maryland's attorney, Katherine Winfree, challenging the value of DNA as a means to identify arrestees, which was one of the state's rationales for using the law.

Roberts raised the point that DNA samples often take weeks or months to be analyzed, which means the information is not available when a judge determines whether a suspect should be freed on bail prior to trial.

Winfree responded that technological advances mean that in the near future samples will be analyzed a lot more quickly.

Her answer appeared to trouble Roberts.

"How can we base a decision today on what could happen in two years?" he asked.

A ruling in favor of King would cast into doubt 27 similar state laws and a complementary federal law. Every other state in the country, plus the District of Columbia and the U.S. territory of Puerto Rico, signed on to a brief in support of Maryland.

King has received full-throated support from civil liberties groups, which are concerned that the government has too few constraints in collecting DNA. At a minimum, police should be required to get a warrant, based on what lawyers call "individualized suspicion," that links a suspect to a particular crime, King's backers say.

There are 1.3 million arrested suspects and 10 million convicted people nationwide whose data has been collected, according to U.S. Federal Bureau of Investigation data. In 2000, there were around 400,000 profiles in the national database. By 2006, there were 4 million.

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