TOKYO (AP) _ Japan's governing coalition officially broke up today ahead of parliamentary elections this summer, bringing an end to a four-year alliance.

Prime Minister Ryutaro Hashimoto accepted the decision of the Social Democratic Party and New Party Sakigake to withdraw from the government.

Hashimoto's Liberal Democratic Party already has assumed all Cabinet posts and enjoys a majority in the more powerful of Japan's two legislative chambers, so the coalition's demise was seen as unlikely to have much impact on the government.

It ended an oddball marriage between the conservative Liberal Democratic Party and left-leaning Social Democrats, formerly Japan's socialist party. Previous to linking up in 1996, the two parties had been political enemies for most of the post-World War II era.

``I value our shared history of having been able to work together,'' Hashimoto said after meeting with heads of the two parties.

Social Democrat head Takako Doi said her party decided to end its alliance with the Liberal Democrats because of disagreements over legislation on political ethics and the strengthening of U.S.-Japan defense ties.

Masayoshi Takemura, chairman of New Party Sakigake, said ``Over the past year, the coalition was mainly driven at the LDP's pace and that left it in bad shape.''

The withdrawal was viewed by many as a tactical move before elections slated for sometime in July. Half the seats in the upper house of parliament will be up for grabs.

The pro-business Liberal Democratic Party has 261 seats in the powerful 500-member lower house. It has 118 seats in the less powerful 252-member upper house, where it relies on support from the 21-member Social Democratic Party and three-member Sakigake for a majority.

The Social Democrats and Sakigake party were expected to continue to vote with the Liberal Democrats on a case-by-case basis. The Social Democrats have pledged to support Hashimoto's administration if opposition parties submit a no-confidence vote against the government.