TOKYO — Just a few months ago, Japan was optimistic about achieving its long-standing dream of a permanent seat on the U.N. Security Council.

The government believed a draft resolution it co-sponsored to expand the council had strong backing in the General Assembly. The United States seemed supportive and U.N. Secretary-General Kofi Annan wanted a quick decision.

But since then, Japan's leaders have watched their dream dissipate.

In its latest quest for a seat, Japan joined forces with Germany, Brazil and India, which also want to be permanent council members. The so-called Group of Four, or G4, talked optimistically about getting two-thirds of the 191 U.N. member states to support its plan to expand the council.

But two rival groups introduced their own resolutions.

An attempt to strike a compromise between the G4 and the 53-nation African Union fizzled in early August. The United States made clear that Security Council reform was not a top priority. Annan backed off his call for the expansion issue to be settled before a U.N. summit in mid-September and is talking about a target of late December.

"Japan has missed a very crucial opportunity to join the Security Council," said Hirokazu Matsumoto, an international-relations specialist. "It's looking very difficult for Japan at the moment."

Japan lavished millions of dollars on General Assembly members in hopes of winning votes for its cause. Foreign Minister Nobutaka Machimura dashed off to Washington for quick talks with Secretary of State Condoleezza Rice to shore up U.S. support.

Tokyo says a seat would help give it political clout more commensurate with its financial power as the world's second-largest economy. Japan also has been a tireless booster of the world body. After the United States, Japan is the second-largest U.N. contributor, pumping in $346.4 million this year, or nearly 20 percent of the U.N. budget. Japan has joined eight U.N. peacekeeping operations, from Cambodia to the Golan Heights, sending a total of 4,600 troops. Tokyo is the world's No. 2 donor of developmental aid.

The G4 proposal would expand the council from 15 to 25 members and give Japan, Germany, Brazil and India veto power just like the current permanent members: the United States, China, Russia, Britain and France. It also would add six permanent seats without veto power.

However, the African Union also wants six permanent seats with veto power, and African leaders rejected a proposed compromise with the G4 countries this month. That shattered the G4's hopes of securing African support, critical for victory in a U.N. General Assembly vote.

Japan also suffers from diplomatic worries closer to home. China opposes Japan's bid. The two Asian rivals are sparring over everything from interpretations of World War II history to territory and undersea resources.