Cooperation is improving between the U.S. and China on exchanging military information and on trying to curb Iran's nuclear programs, the State Department reported Tuesday.

The two nations are also cooperating closely on efforts to stop North Korea's nuclear weapons and missiles programs, Assistant Secretary of State Christopher Hill said at a conference on relations with China. However, he stopped short of predicting that a series of negotiations on North Korea, known as the "six-party" talks, would succeed.

Meanwhile, two senators who say they don't trust China to change its trade policy said Tuesday they will allow the Bush administration's top negotiator a little more time before forcing a vote on punishing tariffs.

After decades of secrecy about its military programs, China is holding talks with the United States on "transparency," said Hill, the State Department official who overseas U.S. policy in Asia. U.S. Adm. William J. Fallon has met with Chinese officials and while China has not abandoned its secret ways, "We are beginning to work with China on seeing what each other is doing," Hill said

Fallon, the commander of all U.S. forces in the Pacific and Asia, told reporters in Washington last week that he was encouraged by the Chinese navy's willingness to participate in a search-and-rescue exercise Sept. 20 with the U.S. Navy off the coast of California, after a Chinese ship visited San Diego.

A more complex version of the exercise is to be held off the coast of China this fall.

Fallon recently visited the Chinese city of Harbin as part of an effort to establish closer ties to Chinese military officials.

Hill said China is "working very closely" with the U.S. on trying to curb Iran's nuclear programs, which the United States says is geared to developing weapons.

He called China a "kindred spirit" with the U.S. on trying to restrain North Korea's nuclear and missiles programs, although he indicated there were some tactical differences.

While China has often publicly urged the United States to be patient with North Korea, Hill said he had asked China to be less patient.

The six-party talks involving the United States, North Korea, China, Japan, South Korea and Russia, have been sidetracked since last November.

"There is no relationship in the world more important for us," than the one with China, Hill said.

"It is not a walk in the woods," Hill said, finding fault with China's record on human rights and religious freedom.

But, he said, "there is a real reason for optimism in the relationship," which is marked also by growing U.S. trade with China, now ranked as the fourth largest economy in the world.

The U.S., however, has as growing trade deficit with China, prompting some in Washington to advocate new tariffs on Chinese goods.

Sen. Charles Schumer, D-N.Y., and Sen. Lindsey Graham, R-S.C., met with Treasury Secretary Henry Paulson as the senators geared up for an expected vote on a Senate bill that would impose a 27.5 percent tariff on Chinese goods.

The senators hope the threat of tariffs will force China to loosen controls on the value of its currency, the yuan. Critics say the yuan's value is artificially undervalued by as much as 40 percent, making Chinese products much cheaper on the world market and hurting U.S. manufacturers.

But after the closed-door meeting with Paulson, the senators voiced renewed hope that the Bush administration, through Paulson, could get results. They said they would take a day or two to decide whether to hold a vote before Congress recesses at the end of the week.

Paulson "is optimistic he can get something done. We believe in him, he's a great guy," said Schumer. As for China, he said, "It's our belief they move when pushed."