TOKYO – Japan's new ruling Democratic Party was set to press ahead on Wednesday with coalition talks that stumbled the previous day over plans for U.S. Marine bases, an issue that could cloud ties with Washington.

Without the cooperation of the tiny Social Democrats and the conservative People's New Party the Democrats lack a majority in the less powerful upper house of parliament.

Despite a landslide victory in the August 30 poll for parliament's powerful lower house, Yukio Hatoyama's Democratic Party of Japan (DPJ) needs their support to ensure legislation can be enacted smoothly, because the upper house can delay bills.

The parties failed on Tuesday to agree on how to word a call for changes to a planned redeployment of U.S. Marines on Japan's southern island of Okinawa, Social Democratic Party executive Yasumasa Shigeno told reporters late on Tuesday.

But Democratic Party Secretary-General Katsuya Okada, set to be foreign minister in the new administration, was optimistic about the outcome of the talks.

Since we had so much debate among the secretaries-general, it's hard to imagine that we won't reach an agreement, he told reporters on Tuesday evening.

One analyst said the delay was likely a performance on the part of the Social Democrats to persuade their supporters that they would have a voice in government, and was therefore unlikely to prevent the formation of a coalition.

They don't really want the whole thing to break down, said politics professor Yoshiaki Kobayashi of Tokyo University.

Decisions will be delayed and the Social Democrats will be critical. But once they have drawn attention to themselves, they will compromise on some deal or other.

The Democrats have vowed to re-think the redeployment plan but may want to play down the issue ahead of Hatoyama's first meeting with U.S. President Barack Obama later this month. U.S. officials have said they will not renegotiate the deal.

The new ruling party's pledge to forge a more independent stance from key security ally Washington has raised concern about possible friction, although Hatoyama has said the alliance remains at the core of Japan's diplomacy.

Hatoyama is set to be voted in as prime minister by parliament on September 16, ending more than half a century of almost unbroken rule by the Liberal Democratic Party and ushering in a government pledged to putting more money in the hands of consumers, cutting waste and reducing bureaucrats' control over policy-making.

(Additional reporting by Sumio Ito and Linda Sieg; Editing by Hugh Lawson)