By MARK SHERMAN

Associated Press

WASHINGTON (AP) - The Supreme Court appeared poised Wednesday to rule that undocumented immigrants who use phony Social Security numbers to get work should not be considered identity thieves, even if those numbers belong to real people.

The court seemed likely to reject the government's argument that, under a 2004 law that metes out a mandatory two-year prison term for "aggravated identity theft," prosecutors do not have to offer any proof that a defendant knew the identification belonged to someone else and was not simply made up.

Should someone get two extra years in prison "if it just so happens that the number you picked out of the air belongs to someone else?" Chief Justice Hon. John Roberts asked Justice Department lawyer Toby Heytens.

In response, Heytens urged the justices to look at the law from the perspective of the victims, who care only that someone is using their seemingly private personal information.

Kevin Russell, a Washington lawyer arguing on behalf of an undocumented worker from Mexico, said there is no question that his client committed a crime by using false documents. But Russell said Congress was trying to toughen penalties for identity thieves who gain access to people's private information to drain their accounts and run up bills in their name.

Undocumented workers commonly buy ID cards from forgers without any intention of invading someone else's privacy, he said. Russell said there are roughly a billion possible Social Security numbers, only about 400 million of which have been used.

Russell's client, Ignacio Carlos Flores-Figueroa, came to the attention of authorities when he decided to drop the assumed name and phony ID numbers he had used for six years. Flores-Figueroa gave his employer his real name and new Social Security and alien registration numbers. Those numbers, however, belonged to real people.

Federal prosecutors won a conviction under the 2004 identity-theft law and the 8th U.S. Circuit Court of Appeals upheld the conviction.

The government has used the charge to persuade people to plead guilty to lesser immigration charges and accept prompt deportation. Many of those undocumented workers had been arrested in immigration raids.

Wednesday, the court's conservative and liberal justices signaled that they have problems with the government's use of the law against defendants without additional evidence that those defendants knew they were invading the privacy of real people.

A decision is expected in the spring.

The case is Flores-Figueroa v. U.S., 08-108.

In Weld County, Colo., District Attorney Ken Buck and the county sheriff seized records from a Greeley income-tax service as part of an identity-theft investigation. Buck alleges that more than 1,300 immigrants filed tax returns with false or stolen identities.

Buck is taking his identity-theft cases to a grand jury after a judge ordered him to stop filing more cases because they included confidential information.