Prime Minister Junichiro Koizumi signaled a historic foreign policy shift Tuesday when he authorized sending Self-Defense Forces units to Iraq, becoming the first Japanese leader since World War II to dispatch troops to a nation effectively at war.

With the move, which comes at the strong urging of the United States, Japan hopes to strengthen relations with its most important ally at a time when government officials boast ties are on their best footing ever.

But sending the SDF to Iraq could actually backfire on relations if Japan suffers casualties.

Critics feel such a scenario would embitter the public toward the U.S., dealing a severe blow to Koizumi's administration, which is already on shaky ground, and to his Liberal Democratic Party and coalition partner New Komeito. They would thus face a difficult battle in next summer's Upper House election.

Tuesday's Cabinet approval of the basic SDF troop dispatch plan comes at a time of heightened public concern over Iraq's security situation in the wake of the Nov. 29 assassination of two Japanese diplomats there.

According to a Kyodo News survey last week, 63 percent of respondents supported the SDF dispatch, but only 7.5 percent believe the troops should be sent quickly.

Reflecting the government's politically difficult situation, the government's plan does not include when the troops will be sent.

More details are expected to be spelled out in deployment guidelines that may be drafted by the Defense Agency later this month. But a top agency official who asked not to be named has already hinted the mission may be further delayed depending on the situation in Iraq.

Defense Agency chief Shigeru Ishiba also indicated Tuesday that the actual SDF deployment timetable may not even be included in the guidelines.

"Without enough training and my conviction (that the safety of the SDF is ensured), there will be no dispatch of the SDF," he said.

Critics say the basic dispatch plan is full of contradictions, especially regarding the war-renouncing Constitution -- contradictions that may put SDF personnel in danger.

The plan allows troops to engage in reconstruction efforts in "noncombat areas" to avoid violating the Constitution, but the government's claim that it can draw a line between a "combat area" and a "noncombat area" is nonsense, they say.

"As the U.S. military says, there is no 'noncombat area' in Iraq," political commentator Hisayuki Miyake said, so the government is trying to send troops to a place that does not exist.

The mission would also be the most heavily armed SDF overseas deployment, allowing troops to carry automatic rifles and antitank rockets. But whether SDF personnel will be able to defend themselves with these weapons is also in question.

Because their use of weapons is legally limited to self-defense, some say there is a high possibility they may be hesitant to open fire unless they come under serious attack.

"If there is a great number of casualties, the Koizumi Cabinet may collapse," Miyake said.

There is also the argument that the deployment under current circumstances is unconstitutional.

Kaoru Okano, a former Meiji University president, said the Cabinet is infringing on the government's official 1981 statement that under the Constitution, Japan cannot engage in collective defense.

Koizumi has said the SDF dispatch would not contradict this, but Okano claims otherwise.

"When Japan's political (authorities) face a new situation, they often try to interpret (the Constitution) in accordance with it," said Okano, an expert on politics.

Instead, he said, Japan should dispatch nonmilitary personnel, including doctors, to join the international community in rebuilding Iraq.

But despite the risks and perceived contradictions, Koizumi is determined to send troops.

"As a responsible member of the international community, Japan should help the people of Iraq so that they can reconstruct their nation with hope," Koizumi said during a news conference Tuesday. "Japan needs to provide not only financial assistance but also supplies and personnel assistance, including the SDF."

Koizumi also hinted that a request from the U.S. affected the decision to send troops, saying Japan should be a "trustworthy ally" of the U.S.

Although Japan's troop levels won't make a big difference in Iraq, U.S. Ambassador Howard Baker said the move will mean a politically significant show of solidarity with the U.S.-led coalition.

The U.S. is engaged in efforts to create a democratic government in Iraq and rebuild the country, which it says is part of its overall war against terrorism.

"It means the coalition against terrorism is extended to the full participation of the second-largest economy of the world," Baker said in a recent lecture at the Foreign Correspondents' Club of Japan in Tokyo.

If Japan decides not to send troops, it would mean Tokyo backed off due to the terrorist attacks believed occurring in Iraq, and that would play into the terrorists' hands, said Akihiko Tanaka, a professor of international relations at the University of Tokyo.

"It would be symbolic if (terrorists) can create the image that Japan, a nation strongly behind the U.S., has dropped out" of the fight against terrorism, Tanaka said.

It is "natural" that reconstruction efforts in a country that just experienced or is in the final stages of a conflict are highly risky, he said.

"But if Japan decided against the dispatch only because of the security threat, it would be considered a nation with little sense of responsibility by the international community," he said.