TOKYO — In the eyes of Shintaro Ishihara and others here, Japan used to be too meek and mild, allowing an overbearing United States to push it around.

Ishihara was one of the authors of the best seller "The Japan That Can Say No," a call for national spine-stiffening that framed the foreign-policy debate here in the 1990s. One of Japan's responses was to build a thriving relationship with China, whether the United States liked it or not.

Now Ishihara and Japanese nationalists like him are at it again, but in reverse. It's an overbearing China that needs to be told no, and the alliance with America should be nurtured, they say.

The latest rallying point involves the economic rights to a large swath of the Pacific Ocean around an uninhabited Japanese atoll 1,100 miles southwest of Tokyo. Ishihara, now the governor of Tokyo, briefed Prime Minister Junichiro Koizumi recently on a plan to cement Japan's claim to the ocean rights by building a power plant near Okinotori Island and encouraging commercial fishing.

"We will conduct economic activities there," the governor said. "We will not let China say anything about it."

Biggest trading partner

That kind of talk breaks with the stereotype of modern Japan's make-no-waves foreign policy and is all the more remarkable considering the huge economic stake Japan has in China. Long the leading destination for Japanese foreign investment, China last week displaced the United States as Japan's biggest single trading partner.

But China's "peaceful rise" makes Japan nervous. It has reacted by building up its lukewarm partnership with the United States into a rock-solid alliance. One major step was to send troops to help the U.S.-led coalition in Iraq, overcoming deep qualms about overseas deployment.

"The Japanese government has been greatly emboldened by the perceived success of the alliance with the United States in the last few years," said Takashi Inoguchi, a Tokyo University professor of international politics.

There is little love lost between Asia's two economic titans. Japan lobbies Europe and Russia not to sell advanced weapons to China's military; China opposes Japan's aspirations to a seat on the U.N. Security Council. China fumes at Japan's friendly relations with Taiwan; Japan wonders why it is giving aid to a nation that has a program to put a man on the moon.

Patience may be spent

For years, Japan reflexively smoothed over any frictions with China. But its patience may be spent. Last November, Japanese destroyers chased a Chinese submarine from the waters around Japan's southernmost islands; in December, Japan formally identified China as a potential military threat. Ignoring Chinese objections, Japan welcomed Lee Teng-hui, a former president of Taiwan, on a visit last month, and the Dalai Lama is expected in April.

Over the past 25 years, Japan has provided China with nearly $30 billion in development loans, a fact rarely mentioned in China's press. During his four years in office, Koizumi has cut development aid to China in half, and he is now considering halting it entirely: "I think it's graduation time," he told reporters recently.

Behind Japan's new attitude is a new postwar generation of politicians, led by Koizumi and Shinzo Abe, now his most likely successor. They think World War II should no longer haunt Japan's relations with its neighbors, but they see in China a growing unwillingness to let it go.

Many Japanese think China's leadership intends to hold on to power by replacing communism with a distinctly anti-Japanese nationalism. Surveys of Chinese young adults find them much more anti-Japanese than their parents and grandparents.

Those attitudes and China's bias in favor of sons, which by 2020 may produce a population with 40 million more young men than young women, could be a combustible mixture. A taste of the danger came at a China-Japan soccer match last August in Beijing. Chinese fans screamed, "little Japan, petty Japan" at television cameras and then rioted after the game, burning Japanese flags.

Many Japanese suspect that the Chinese authorities allow such incidents as a way to let off steam in a politically closed society. "The masses sense they can pretty much get away with anything when Japan is the target," wrote Yoichi Funabashi, Japan's leading foreign-affairs columnist.

Ma Licheng, an independent Chinese academic, wrote in Japan Echo magazine: "The fact is that China has nothing to fear from Japan today; indeed, it is the Japanese who regard China with trepidation. The doctrine of the 'Chinese threat' is gradually taking hold in Japan."

Japanese leaders increasingly talk of the relationship with the United States as overridingly important.

"The future of Asia will be decided by the two-way balance between China and the U.S.-Japan alliance, not a trilateral balance among the three countries," says Hisahiko Okazaki, a retired Japanese diplomat. "What is Japan's China policy in the future? Strengthen the U.S.-Japan alliance. What to do about North Korea? Strengthen the U.S.-Japan alliance."

The emerging dynamic with China is often described here as "cold politics, hot economics." Some 18,000 Japanese companies have operations in China now, about twice as many as a decade ago. Matsushita Electric Industrial, parent of Panasonic, expects to hire more Chinese college graduates this year than Japanese graduates.

But Japanese business leaders worry that frosty political relations and street-level hostility are undermining Japan's economic appeal in China. Beyond sporadic calls for boycotts of Japanese goods, they see a threat to big contracts. Last fall, an order for high-speed trains was cut to $1 billion, half the expected amount, after a lightning Internet campaign protested Japan's "involvement in China's railway industry." Unnerved officials in Beijing ordered the protest Web site shut down.

Over the long term, the economic trajectories of the two countries are clear. Barring catastrophes, "China will become the sole leader in Asia, with Japan as an important subordinate," Toyoo Gyohten, a Japanese business leader, warned in a speech last fall.

Gyohten questioned the wisdom of antagonizing China out of pique over Chinese harping on World War II and the invasion by Japan. "Many Japanese believe they have already apologized," he said. "But I, for one, believe that we should apologize as many times as possible."

But for Koizumi, Ishihara and their generation, there is a statute of limitations on contrition. As Kingston, director of Asian Studies at Temple University Japan, said: "This is a Japan that doesn't flinch any more."