When Rohan Coombs joined the Marine Corps, he never thought one day he would be locked up in an immigration detention center and facing deportation from the country he had vowed to defend.

Coombs, 43, born in Jamaica, immigrated to the United States legally as a child with his family. He signed up to serve his adopted nation for six years -- first in Japan and the Philippines, then in the Persian Gulf during the first war with Iraq.

Up to 8,000 noncitizens enlist in the armed forces every year and serve alongside American troops. As of May 2010, there were 16,966 noncitizens on active duty. The military does not allow illegal immigrants to enlist.

If noncitizens die while serving, they are given citizenship and a military funeral. If they live and get in trouble with the law, as Coombs did -- he was court-martialed for possession of cocaine and marijuana with the intent to distribute -- they can get caught in the net of a 1996 immigration law that greatly expanded the list of crimes for which noncitizens can be deported.

"As far as I was concerned, I was a citizen," said Coombs, whose soft-spoken, introspective nature contrasts with his physical presence. Coombs stands 6 feet 5 inches and weighs more than 260 pounds -- a gentle giant, according to his fiancee, Robyn Sword.

Now, advocates of noncitizen service members are pushing for change. Attorneys are taking cases like Coombs' to court, arguing that an immigrant who serves in the armed forces should be considered a U.S. national and protected from deportation.

"These are people who served us -- whether they are model human beings or not," said Coombs' attorney, Craig Shagin of Harrisburg, Pa. "They served in our uniforms, in our wars. If they were POWs, they'd be considered American prisoners."

Rep. Bob Filner, D-Chula Vista, chairman of the House Veterans' Affairs Committee, is looking into potential changes to the law so immigrants who serve in the military can avoid deportation.

"You come back from Iraq or Afghanistan today, you have put yourself on the line for this country," Filner said. "An incredible number of kids come back with an injury or illness that puts them in trouble with the law. To simply have these people deported is not a good way to thank them for their service."

Advocates estimate that thousands of veterans have been deported or are in detention. Government officials say they have no tally but plan to begin tracking the numbers.

The push comes as criminal courts are increasingly listening to arguments for leniency for veterans.

So-called veterans courts, which give them specialized treatment, now number more than 30, with a dozen more planned.

Next month, new U.S. Sentencing Commission rules will make it possible for federal judges to consider a criminal defendant's military service and mental and emotional condition to issue a lesser prison sentence. The rules, however, would not apply to immigration judges.