For decades, Japanese soldiers in Asahikawa (search) trained for a Soviet invasion that never came.

Now this frigid northern tip of Japan is again on a front-line of sorts: Hundreds of troops here are mobilized for a humanitarian mission in Iraq that will put the country's soldiers in a combat zone for the first time since World War II.

The prospect has divided the Japanese and fueled a debate about the role of its military.

"Of course we have a responsibility to help Iraq," said Toshiaki Nomiya, a 42-year-old graphic artist who lives in this city of 360,000 people. "But we can't just ignore on the lessons of history and let this country get dragged into another war."

The national debate hits home in Asahikawa. The base on Japan's northernmost main island, which houses an armored division, is supplying almost all the 600 ground troops headed to Iraq for humanitarian duties such as rebuilding schools and supplying water.

The deployment is part of a total of 1,000 Japanese military personnel going to Iraq, Kuwait and Qatar. This week, a small military team flew from Tokyo to inspect the city in southern Iraq where the Japanese contingent will be based; on Friday an advance team of some 30 ground troops left for Kuwait for training before heading to Iraq. The rest of the force could start leaving this month.

The dispatch presents Prime Minister Junichiro Koizumi with his toughest test since taking office two years ago.

Koizumi argues that Japan is fulfilling its international commitments, and he is eager to erase Japan's lingering image from the 1991 Gulf War (search) as a country willing to pay for fighting but reluctant to risk its own troops.

The prime minister is also building momentum for a historic rethinking of the constraints placed on the military by the war-renouncing 1947 constitution, written by the United States. His party is drafting a revision of the document, which has never been amended.

The project faces stiff resistance in Japan, where the World War II defeat and the atomic bombings of Hiroshima (search) and Nagasaki (search) are considered horrifying reminders of the devastation of war. Many see the constitution as insurance against a return of militarism.

The Iraqi mission carries high political risks. Upper house parliamentary elections are scheduled in six months, and Koizumi's government could be weakened if Japan starts suffering casualties in Iraq. The main opposition party calls the Iraq mission reckless.

"Koizumi wants to bury the whole checkbook diplomacy thing," said Tomoaki Iwai, a professor at Tokiwa University. "But that doesn't mean much to people who think he's risking Japanese lives for a war that wasn't justified in the first place."

Asahikawa has experienced firsthand the recent changes in Japanese military policy that have been accelerated by the prime minister.

Troops began shipping out a decade ago after Japanese lawmakers gave approval for the military to carry out noncombat duties with United Nations peacekeeping operations. Plaques in a dusty museum on base mark the division's participation in U.N. missions from Cambodia to the Golan Heights to Rwanda.

But Japanese peacekeepers have never before been sent into a country where guerrilla attacks were a daily threat. And no Japanese peacekeeper has ever been killed.

"There's no turning back for Japan if our troops are sent into a combat zone," said peace activist Hisashi Yui, 30. "It's like the constitution is being ripped up a bit at a time."

Yui helped organized a demonstration last month that brought 2,000 protesters to the front gate of the base. Antiwar groups have vowed to continue the fight.

Koizumi says fact-finding missions have shown southern Iraq is "relatively stable." But glimpses of the preparations in Asahikawa have sent a different message.

Media access to the base and soldiers is tightly restricted. At a rare training session open to reporters, cameras followed troops as they were put through their paces pumping water from a camouflaged tanker truck. But the rest of the hardware suggested the dangers they would face: automatic weapons, rocket-propelled grenades, armored personnel carriers.

Next to the base stands a Shinto shrine dedicated to the region's war dead. Every day, the priest prays for the souls of 66,000 fallen soldiers. More recently he has begun praying for something else.

"All those who have given their lives for this country can find repose here," said Tsuneya Shiyonoya. "But we just want the troops to come back safely."