TOKYO, May 15 (Reuters) - Japan's parliament on Tuesday passed a bill extending air force support for the U.S.-led war in Iraq for another two years, despite opposition calls for the troops to be brought home.

Japan, whose military activities are strictly curtailed by its pacifist constitution, pulled its 600 ground troops out of a non-combat reconstruction mission to southern Iraq last year.

About 200 Japanese air troops have been operating cargo and personnel flights for the United States and its allies into Iraq from a base in Kuwait since 2004.

The bill easily passed the powerful lower house thanks to the overwhelming majority held by the ruling Liberal Democratic Party (LDP) and its junior coalition party New Komeito, who also voted down an opposition bill that would have ended the mission.

The main opposition Democrats and other opposition parties argued that since no weapons of mass destruction had been found in Iraq, there was no justification for the war.

"We cannot accept the spurious argument that the evidence was wrong, but the decision was right," one opposition politician told parliament.

Prime Minister Shinzo Abe, a staunch ally of the United States, was grilled by a parliamentary panel on Monday about his motives for continuing to support President George W. Bush's Iraq policy.

Abe, who visited the Kuwait base to thank the troops earlier this month, replied that since Japan imported nearly 90 percent of its oil from Middle East, the region's peace and stability was a matter of Japan's national interest.

The bill's passage came a day after Japan enacted a law outlining steps for a referendum on revising the constitution. The LDP wants the charter to make clear Japan's right to maintain a military, as the government tries to boost the country's role in international security.

Opinion polls showed that the public largely opposed the dispatch to Iraq, but rated the ground troops' performance highly after they returned without suffering casualties or firing a shot.

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