CAMP FOSTER, Japan — Lance Cpl. Alexander Karman is waiting around the barracks for his friends to finish up so they can head to the gym and a karaoke joint just outside the gates. This is Karman's last payday on Okinawa, and he has to report back for duty at 3 a.m.

Karman's three bags of gear have been inspected and stowed in the locker next to his bunk. The scope on his M-4 rifle has been adjusted. The 21-year-old explosives disposal specialist from Miami has finished the physicals, the marksmanship qualifications, the lectures on how to write a will.

His next stop: Iraq.

The deployment now under way from the Japanese island of Okinawa — site of a famous World War II battle and one of the Pentagon's most important outposts in the region — reflects shifts in both Washington and Tokyo.

It's part of Washington's increased emphasis on military mobility and the option to move forces to hotspots as needed. But Iraq has pushed this doctrine to the limits, pulling in troops already sent abroad on another mission. In Okinawa's case, it's no small assignment: countering potential threats from North Korea and the growth of China's military.

Japan, too, has been forced to examine what it means to host 50,000 U.S. soldiers spread across Okinawa and other bases. A debate rumbles over the role of American forces in Japan: whether to only fulfill a mutual security pact, or also to be battlefield resources for wars elsewhere.

And for the Iraq-bound troops, it's a little like deploying from limbo.

Karman, who like many in his unit has already been in Japan for about a year, said goodbye to his mother, father and fiancee at Florida's Fort Lauderdale airport last month while on leave. They already knew they were in effect seeing him off to Iraq.

Now that he's back on Okinawa, there won't be anyone to see him off.

"It's hard," he said, a big American flag from Wal-Mart pinned up beside the desk he shares with three roommates. "You get adjusted to life here, then you have to go home and say your goodbyes, then come back and wait. I just want to get going."

What they'll leave behind is Japan's version of Hawai'i.

Every August, the island's hotels swell with newlyweds and families with small children. Airlines promote Okinawa, which lies 1,000 miles southwest of Tokyo and was once an independent kingdom, as a "Paradise Island."

But the Marines live in a very different world.

There's a midnight curfew for enlisted troops. Drinking is tightly restricted. Car ownership is banned.

And then there's the money. A private makes about $1,000 a month, which doesn't go far on Okinawa. The Japanese tourists on the beach are likely to be making at least twice as much as the Marines.

Few married Marines are allowed to bring their wives and children. But that also makes them more willing to head off into the dangers of Iraq.

"I want to see more action, to do my part," said Cpl. Thomas Williams, from Lexington, N.C. "But I also just want to get out of Camp Schwab." Schwab is one of several Marine camps spread across the island.

The 1,000-strong battalion heading to Iraq is just a small part of the nearly 15,000 Marines based across Okinawa.

Until now, the Okinawa Marines sent only small contingents to Iraq to help other units. But with American forces around the world stretched thin — and with the demands in Iraq not easing up — the Pentagon has decided more help is needed.

In Japan, this feeds a debate that began with the 2003 invasion to topple Saddam Hussein.

Japan struggled over how much to support its American ally and whether U.S. forces in Japan should stay out of the fight. Opponents argued that U.S. troops are in Japan under a mutual security pact, not as a forward-based force for America's battles around the world.

Keeping young Marines who are far away from home — often for the first time — both in line and combat-ready is no easy task.

"It's been a learning curve. It hasn't been ideal, but we are used to that in the Marine Corps," said Lt. Col. Brent Spahn, the battalion's commanding officer. "We train hard, and we think our training is the best in the world. You fall back on that. That's what gets you through."

Spahn said his main concern isn't getting the troops motivated to go, but keeping them reined in once they get to Iraq and start their primary mission, which will be running convoys.

"The Marine Corps doesn't recruit the same kind of people as the other branches of the military. We tend to get aggressive people, which is good if you want a strong military," he said. "My biggest concern will be keeping the enthusiasm and the adrenalin under control."