SINGAPORE - The United States and its Asian allies are laying the groundwork for a tougher stance toward North Korea should negotiations with China and Russia fail to yield a new strategy to force the North Korean government to give up its nuclear program, defense officials said yesterday.

During a meeting, U.S. Defense Secretary Robert M. Gates told his South Korean and Japanese counterparts that they should begin thinking about measures the three countries could take unilaterally if the so-called six-party talks continued to founder.

Gates "raised the notion that we should think about this as we are pursuing the six-party talks," said a senior defense official, speaking on condition of anonymity because of diplomatic protocol. "We ought to think about what more we need to do should they not prove successful."

U.S. defense officials stressed that they still hoped to revive the six-party talks. A high-level delegation led by a top State Department official, James B. Steinberg, will begin a series of meetings this week in Tokyo; Seoul, South Korea; Beijing; and possibly Moscow aimed at hashing out a consensus on North Korea.

In April, North Korea said it would "never again" participate in the talks after the United Nations rebuked its rocket launch over Japan.

But in the past, Gates had been dismissive of the talks, and U.S. officials had privately worried about Russia's commitment to intensifying pressure on North Korea.

If a multilateral approach showed signs of failing, officials said, the United States would begin discussions about the need to develop "prudent measures" it could take with South Korea and Japan.

But China yesterday signaled its displeasure with that prospect.

"China opposes the enlargement of the existing bilateral military alliances in Asia-Pacific, which were left over from the Cold War," Lt. Gen. Ma Xiaotian, the People's Liberation Army's deputy chief of the general staff, said in a speech to an Asian security summit in Singapore.

After the speech, Ma said that he understood South Korea and Japan's concerns about North Korea's recent nuclear test, and that China shared them.

"As a close neighbor of North Korea, China has expressed our firm opposition, our grave concern about the nuclear test," Ma said. "We are resolutely opposed to nuclear proliferation."

But it was unclear whether China would go as far as the United States wanted in pressuring North Korea to give up its weapons program. Ma called on the countries involved to "remain coolheaded and take measured measures."

In the meeting among the United States, South Korea and Japan, the defense ministers discussed no specifics of new measures they should take.

"There is no prescription yet on what to do, but there are lots of ideas," said another senior defense official.

Additional measures could include moving forces around, or into, the region and shoring up missile defenses in South Korea or Japan.

In the meeting, the officials from the three countries discussed the necessity of not appearing to reward North Korea for its test by offering it any concessions.

"We have evaluated the situation and pledged to craft a common response," South Korean Defense Minister Lee Sang-hee said. "North Korea, perhaps to this point, may have mistakenly believed it could be rewarded for its behavior, but that is no longer the case."