While the United States has been preoccupied with Iraq, a shuffling of alliances is taking place in Northeast Asia, accelerated by the U.S. failure to defuse the North Korean nuclear crisis, according to government officials and analysts.

The result is likely to be a crumbling of Cold War ties and a lessening of U.S. power and prestige in a region where the United States has held sway for 50 years, they said.

The key shift is on the Korean Peninsula, where South Koreans and their new government are increasingly unwilling to play the role of loyal supporter of the United States.

The result is a weakening of the two three-legged alliances that have defined relations in the region ever since Soviet and Allied forces came nose-to-nose on the Korean Peninsula at the end of World War II: the United States, Japan and South Korea on one side, and Russia, China and North Korea on the other.

"There is a reshuffling of relationships. One worrying symptom is the deterioration of the South Korea-U.S. relationship," said Yukio Okamoto, a private consultant and close adviser to Japan's prime minister, Junichiro Koizumi.

South Koreans anticipate a future with formal ties or even a loose union of some sort with North Korea, its foe in the 1950-53 Korean War and with whom it has still not signed a peace treaty. And South Korea is steadily improving ties with China, which fought alongside North Korea, and -- with the North and the Soviet Union -- formed the heart of the Communist Bloc opposing the United States.

Other political reorderings are undoing those old power blocs. China and Russia now set their foreign policies on pragmatic terms, not ideology. North Korea's ties to its former communist allies have become more strained as China and Russia look disapprovingly at Pyongyang's nuclear ambitions.

Even Japan, while remaining the most determined ally of the United States, is reaching out to old enemies. It forged a historic agreement with North Korea last September with only cursory consultation with Washington, and is improving relations with China, South Korea and Russia -- all wartime enemies or conquests.

The Korean Peninsula is often said to be one of the few places in the world where the Cold War endures. But, "what we are talking about is the Cold War unraveling," Leon V. Sigal, author of "Disarming Strangers: Nuclear Diplomacy with North Korea," said in an interview in Seoul.

Some of these changes have been developing for years. But experts say the dispute over North Korea's development of nuclear weapons fuel has caused governments to look more urgently at other potential partners, because they see the United States as an obstacle to peaceful relations in the region.

"We are setting ourselves up as the source of instability in the region" by squaring off against North Korea and promoting a missile defense system that could prompt an arms race in the region, Sigal said.

"Everybody out here is cooperating to try to get the Americans to play" by negotiating with North Korea, he said. "If the Americans don't play, the other countries will do it themselves. It could end up with everybody quietly collaborating against us."

North Korea said today that it was postponing talks with South Korea on marine cooperation and economic exchanges, blaming the move on South Korea for beefing up its defenses after U.S.-led forces launched military strikes against Iraq. In Beijing, a U.N. envoy said North Korea was concerned it would be the next U.S. target after Iraq.

The possibility of diminished U.S. authority in the region troubles officials in Japan, which has cast its lot squarely with the United States. Koizumi this week bucked public and political opposition and endorsed a U.S. attack on Iraq, in what officials say is a loyalty payment and insurance of U.S. support against North Korea.

Tokyo anticipates a struggle to retain U.S. influence in the region as China's grows, a top Foreign Ministry official said.

"We may be the only ones in this Asia Pacific region who are saying, 'We have to see how [new arrangements] are compatible with the U.S. presence,' " said the official, who requested anonymity. "We have to say that we still need the United States in the region."

In an interview in the prime minister's office complex, Okamoto noted the precedent of the Philippines, where anti-U.S. sentiment prompted the United States to abandon a major naval base. "We hope it doesn't happen in South Korea," he said.

The new South Korean administration has concluded it still needs U.S. troops, despite campaign calls by the new president, Roh Moo Hyun, for more "balance" in the U.S. relationship.

"A more balanced relationship between Seoul and Washington means a shift from patron-client to more partnership," said Kim Sung Han, an expert with a policy institute created by the South Korean Foreign Ministry. "It doesn't necessarily mean a dissolution of the U.S. military presence here."

But public opinion is more severe, and the public is more willing to scrap U.S. ties.

"The man on the street in Seoul points at Bush as the one with the biggest responsibility for the state of anti-Americanism today," Kim Myong Sik, chairman of South Korea's Arirang TV, wrote recently. "Bush's repeated derogatory remarks about North Korean leader Kim Jong Il irk even the moderately conservative audience here in Seoul."

That public mood is reflected elsewhere in the region, where governments are beginning to question long-standing policies.

"The realignments are occurring sort of pell-mell as each country tries to find out what to do," K.A. "Tony" Namkung, a consultant who works with the Japanese and South Korean governments on North Korean policy matters, said in Tokyo. Washington, he said, has been "clueless" to these shifts.

"There was never a reassessment in this part of Asia of its alliances after the Cold War, because the Cold War never ended here," said Scott Snyder, who represents the Asia Foundation in Seoul. "Now there is."

Only the mutual interdependence of Japan and the United States remains unshaken. Japan depends on U.S. military, nuclear and overarching political protection; Washington relies on Japan as an Asian base for its troops, a stable economy and trading partner and big donor to projects ranging from rebuilding Afghanistan to refueling U.S. warships.

But Koizumi's surprise decision to hold a summit last September with Kim Jong Il, culminating in the first-ever formal pact between the countries, "would have been inconceivable" without U.S. approval a few years ago, Namkung said.

Even Tokyo quietly joined other allies in resisting Washington's hard-line approach to North Korea. The Bush administration turned for help to China, but has found Beijing resentful of Washington and claiming inadequate leverage with the North. Russia sent an emissary to Kim Jong Il, but the entreaties of both former communist patrons, which once Pyongyang would have felt required to accommodate, were politely ignored.

"This crisis is most serious, in that it could cost us our relations with the whole region," said Selig S. Harrison, director of the Asia Program at the Center for International Policy, a Washington research organization, who recently headed a panel of experts studying the North Korean dispute.

A South Korean student is pulled by riot police on one side and fellow protesters on the other during an antiwar demonstration in Seoul, where anti-American sentiment has grown.