“One has to marvel at the enormity of the investment by the People’s Liberation Army in submarines,” said Richard Fisher, a specialist on the Chinese military.

China also is building two nuclear-powered submarines — one Type 093, believed to be based on the Russian Victor-III class and armed with intercontinental ballistic missiles, and a Type 094 attack submarine, which the Pentagon believes has a finished hull and will be ready for deployment next year.

According to Mr. Trevethan, China currently has a force of 57 deployed submarines, including one Xia-class nuclear ballistic missile submarine, five Han submarines, four Kilos, seven Songs, 18 Mings and 22 Soviet-designed Romeos. Beijing also has eight more Kilos on order with Russia.

Disclosure of the new submarine comes as the United States is trying to sell eight diesel submarines to Taiwan, which Beijing views as a breakaway province. Taiwan currently has just two World War II-era Guppy-class submarines and two 1980s Dutch submarines.

Mr. Fisher, an analyst with the International Assessment and Strategy Center, said that despite the imbalance of power on the Taiwan Strait in favor of Beijing, the Bush administration has been slow to sell the submarines it offered Taiwan in April 2001.

“It is simply appalling that the United States cannot get its act together to organize the production of eight new submarines for Taiwan,” Mr. Fisher said.

U.S. defense officials have said delays with the Taiwan submarine deal are the result of the Taipei government’s budget problems.

Chinese leaders told National Security Adviser Condoleezza Rice last week that China would “not sit idly by” as Taiwan moved toward formal independence, and President Hu Jintao denounced U.S. weapons sales to Taiwan.

But Miss Rice said the United States will go ahead with its Taiwan arms sales plan because of China’s missile buildup opposite the island.

A Pentagon report made public in May stated that China is changing its warship forces from a coastal defense force to one employing “active offshore defense.”

“This change in operations requires newer, more modern warships and submarines capable of operating at greater distances from China’s coast for longer periods,” the report said, noting that submarine construction is a top priority.

Mr. Fisher said the Chinese submarine buildup should prompt the Pentagon to step up U.S. anti-submarine warfare capabilities, which he said are “at an historic low” because of cutbacks in specialized ships and aircraft.

The Navy should consider building its own diesel attack submarine to be able to “effectively duke it out with the new tidal wave of Chinese subs, that if left unchecked, may soon dominate the Asian littoral regions,” Mr. Fisher said.

The Pentagon is also building up U.S. naval forces in the Pacific, with the addition of up to six attack submarines in Guam and the possible deployment of an aircraft carrier battle group to Hawaii in the coming months.