ASHINGTON, July 26 ? In a highly contentious vote, Japan's Parliament approved legislation today that paves the way for Tokyo to send as many as 1,000 troops to Iraq later this year as part of the American-led occupation.

The deployment would be the first for Japanese troops in a combat zone since World War II. In the past decade, Japan has sent small forces to peacekeeping operations in Cambodia and East Timor. After the attacks on the United States on Sept. 11, 2001, Japan sent warships to patrol the Indian Ocean.

Today's vote, 136 to 102, was a major victory for Prime Minister Junichiro Koizumi, who defeated opposition tactics, a no-confidence vote and a filibuster by the bill's opponents to ram the measure through.

Shortly after the bill's passage, Mr. Koizumi told reporters that he would press hard in the weeks ahead to gain public support for the deployment. An opinion poll in the liberal daily Asahi Shimbun on Tuesday showed that 55 percent of the Japanese interviewed opposed sending troops to Iraq, compared with 33 percent who supported it.

"When we look back in the future, they will think the legislation was good for the country," the Jiji Press news agency quoted Mr. Koizumi as saying.

Pentagon and State Department officials in Washington praised Japan's decision as supporting the administration's flagging effort to recruit international peacekeepers and donors to help rebuild Iraq. Japan is already a leading financial contributor, pledging $86 million in aid.

"We recognize what an important issue this is and how it's an important development for Japan, which we welcome," the State Department spokesman, Richard A. Boucher, told reporters here on Friday as the bill moved through Parliament. "We think that Japan's ability to play this positive role in Iraq is a reflection of the kind of role it can play in world affairs."

A Pentagon spokesman, Bryan G. Whitman, also welcomed Japan's decision but said it was too early to tell when and what role Japanese forces might serve in Iraq.

There are about 148,000 American troops and 13,000 other allied forces in Iraq now, and Pentagon officials say allied countries have promised a total of about 30,000 troops by later this summer.

But several countries with large potential contributions, including India, Pakistan and France, have balked at taking part under the current United Nations resolution, which they say does not permit their military involvement.

The vote by Parliament was a formality because it is dominated by the governing Liberal Democratic Party. The real test will be in deciding what role the troops will play.

Japanese troops have not taken part in combat operations since the end of World War II, and under the law passed today, the troops would be limited to noncombat areas where they could help resettle refugees, rebuild schools or factories and provide fresh water and supplies.

But opponents of the measure say there are no noncombat areas in Iraq, given the guerrilla attacks throughout many parts of the country. These opponents assert that the law violates Japan's post-World War II Constitution, which bans the use of force to settle international disputes.

Prime Minister Koizumi said the government would need to conduct a "thorough study on local conditions" before deciding exactly how many and what kind of forces to send. A reconnaissance mission was reportedly ready to leave for Iraq as early as next month.

The matter will almost certainly become a difficult issue for Mr. Koizumi if troops have to engage in combat, but he will probably delay any decision on that until after Japan's general elections in November.

People in Japan say Iraq will likely come up as a campaign issue, and many express concern that if Japanese troops are sent to Iraq, it could set a precedent for other, more dangerous military missions.

"This is a very significant development," said Paul Stares, a Japan expert at the United States Institute of Peace, a research organization in Washington. "We've seen, since 9/11, an incremental shift in Japan's security policy and a willingness to contribute to broader security issues."

Final approval for the bill did not come without a fight. The voting was delayed for hours by stalling tactics from the opposition parties, including an unsuccessful motion of no confidence in Mr. Koizumi on grounds that deploying troops to Iraq would violate Japan's Constitution.

Yelling and scrambling opposition lawmakers surrounded the committee chairman dealing with the Iraq motion but were unable to stop the passage of the bill by the committee and a later plenary session.