The head of Japan's largest opposition party, Katsuya Okada, will visit Boston during the Democratic National Convention next week on a tour designed to bolster his ties with the United States, this nation's most important ally.

Analysts said gains made by Okada's Democratic Party of Japan in upper house elections this month have positioned him as a contender to eventually unseat Prime Minister Junichiro Koizumi and his Liberal Democratic Party -- the conservative political force that has ruled Japan for most of the post-World War II era.

The rise of the Democratic Party is being seen as a step toward a two-party system in Japan, similar to the rivalry of the Labor and Conservative parties in Britain.

Okada's first stop in the United States will be in Boston on Tuesday, when he hopes to pick up some political pointers at the Democratic convention, he said in an interview Wednesday.

With about one-third of Japanese voters remaining independents, one of the opposition's great disadvantages against the Liberal Democrats has been its inability to establish grass-roots support in rural areas of Japan. Okada said Wednesday that he is fascinated by the U.S. national conventions and other methods of building party allegiance.

"I'd like to learn their tactics for attracting voters," said Okada, 51. He said he sees affinities between his own party and Democrats in the United States: "We share the same name" and have "quite a lot of similarities in the way we think."

"But the Republicans are the ruling party, so our relations with them are important as well," Okada said. To that end, he also plans to meet with Bush administration officials in Washington.

His reception there, however, is likely to be less enthusiastic. Okada and his party have opposed Koizumi's decision to support the U.S.-led invasion of Iraq and contribute noncombat troops to the reconstruction effort there. On Wednesday, Okada criticized Koizumi -- the Bush administration's closest ally in Asia -- for dispatching forces against the will of most Japanese. Polls show the public largely opposed to the Iraq mission.

Okada said he favors maintaining a strong U.S.-Japan alliance, especially given the threat of North Korea developing nuclear capacity just across the Sea of Japan. However, he added that he would favor the relocation of at least some U.S. troops away from the southern island of Okinawa, where residents have expressed the desire for a reduction in the American presence.

Additionally, he said that given advances in U.S. military weaponry and capabilities, he would not oppose an overall reduction of U.S. troops in Japan. He cited a similar plan by the U.S. government to withdraw as many as a third of its 37,000 troops in neighboring South Korea by the end of next year.

Katsuya Okada says he is fascinated by American political methods.