As thousands of Marines are preparing to ship out to the Persian Gulf within the week, one leatherneck is making his mark on American Idol instead.

Lance Cpl. Josh Gracin, 21, was slated to be deployed with his unit in Kuwait in the coming days.

But his mother said that when he got his big break to appear on the popular Fox show, Marine brass made an exception for him.

Brenda Gracin, of Westland, Mich., said "higher authorities" intervened on behalf of her singing offspring to delay his posting to the Mideast hot spot.

"American Idol had to work with Washington to get Josh out of the deployment," Mrs. Gracin told a source.

But she added that her son was not shirking his duty and "once his stint on American Idol is over, Josh will be sent to Kuwait."

Gracin is slated to appear on the show Wednesday night.

The delay deployment may turn into a musical minefield.

As the nation gears up for war in Iraq and families are split, Gracin's apparent exemption could hit a sour note with veterans, military personnel and other patriotic Americans.

"We're under strict instructions not to say anything," Brenda Gracin told The Post yesterday. She said she didn't know how long the Marine's deployment was deferred.

"But I'll tell you one thing: we're very proud of him."

The singing Marine came to the attention of the show's producers when they played his audition tape on national TV Wednesday.

More than 25 million people watched as Gracin sang the Frank Sinatra chestnut, "All or Nothing at All."

He even got a thumbs up from Brit bully Simon Cowell, one of the judges. Known for his caustic comments targeting untalented contestants, Cowell heaped praise on the Marine.

The show received about 70,000 entries for this year's program that aims to turn nobodies into pop stars.

Neither show officials nor the Marines returned calls from The Post yesterday.

Gracin joined the Marines two years ago and is assigned to Camp Pendleton, Calif. Already, 200 of his fellow Marines have been deployed in Kuwait and Qatar. An additional 2,100 leathernecks from his base are slated to be in harm's way in a week.

His father, Mario, said the Marine has been studying finance and accounting at the base, where he is "in charge of" supplies.

Gracin has always had a song in his heart, according to his father who revealed he played saxophone in the John Glenn high school band in the late 1990s.

He later switched to guitar and began performing at community events. In 1997, he even put out a country single called "She Loves Me."

Gracin's story stands in stark contrast to Harlem couple Lateef and Claudia Bost.

Lateef was doing five months of basic training at Fort Jackson, S.C., and Claudia was still doing her stint at Fort Jackson when her husband was called to active duty.

Claudia finished training last week and came home. Lateef Bost hopes to see her and son Lateef Jr. before he's shipped overseas.