TOKYO (Reuters) - Only a third of Japanese think ties with the United States, Tokyo's most important security ally, are in good shape, according to a poll released just weeks before President-elect Barack Obama takes office.

The level of Japanese dissatisfaction -- the worst since 2000 -- reflects unhappiness at Washington's removal of North Korea from its terrorism blacklist and declining confidence in the U.S. economy in the wake of the global financial crisis, the Yomiuri daily, which published the poll, said on Thursday.

Many Japanese also fear Washington may focus on building stronger ties with a rising China while losing interest in Japan.

About 1,000 people in Japan and also the United States were surveyed by the Yomiuri and Gallup, the newspaper said. More than half of the Americans surveyed said ties with Japan were good.

For most of 2001-2006, about half of Japanese respondents in similar surveys said they thought Japan-U.S. relations were good.

That was partly due to warm ties between President George W. Bush and former Japanese prime minister Junichiro Koizumi, who served a full five-year term.

Since then, Japan has had three prime ministers. The current premier, Taro Aso, is struggling to keep his job with his support ratings tumbling.

The Yomiuri/Gallup survey showed three quarters of Japanese respondents thought the two nations were not cooperating well over North Korea.

Japan has been trying to resolve an emotive dispute with North Korea over Japanese citizens abducted by Pyongyang decades ago. Many Japanese were upset by Washington's decision to take the secretive communist state off its terrorist blacklist in October for making progress in nuclear disarmament.

U.S. experts sought to ease worries about the alliance.

"We want good relations with China, but in my view we cannot have good relations with China unless we have excellent relations with Japan," John Hamre, a former U.S. deputy secretary of defense, said at a symposium in Tokyo on Thursday.

He said Japan-U.S. ties were strong and at a new level, noting no one in the United States had blamed Japan or Japanese automakers for the woes facing U.S. carmakers, as some politicians did in the 1980s and 1990s.

But Hamre said such ties should not be taken for granted and should be given attention by the Obama administration.

"If I have one concern, it is that relations between our two countries are so good that they are not very exciting. And in many ways, U.S.-Japan relations are like an old married couple that go out to dinner in a restaurant and never talk to each other," he said.

"We've got to start talking about it together. We've got to revalidate the foundation of this relationship ... that's going to be a starting point for this new administration," he added.

(Reporting by Yoko Nishikawa, Editing by Dean Yates)