The United States is having some success encouraging China to be more transparent about its military, the top US commander in the Pacific said.

But Adm. William Fallon said Beijing would need to open up further before he would suggest that Congress loosen restrictions on military contact between the two Pacific powers.

"I think we're making progress. And I'd like to see us continue to move down this path," Fallon said in an interview on Monday. "Then I'd feel more comfortable going back to Washington and recommending they make some adjustments."

US law limits exposure of the Chinese military to certain US operational areas and requires the US military to submit annual reports of its contacts with the People's Liberation Army.

Fallon added he would need to see "continued movement" from China before he suggests that Congress change the law.

He said that would mean a "real, transparent, two-way relationship here. And not just us offering things. It needs to really be developed," Fallon said.

Fallon has pushed to increase bilateral military contacts since he assumed control of the Pacific Command in February last year, saying the two countries must understand each other to avoid miscalculation.

Military ties between the United States and China have never been close but they deteriorated after a US Navy spy plane and a Chinese fighter jet collided off China's southern coast in 2001.

Fallon, along with Defense Secretary Donald Rumsfeld and other officials have repeatedly called on China to explain why it is rapidly modernizing its military and has boosted its annual military spending by double-digit percentages for about a decade.

Rumsfeld approved increasing exchanges last October during a visit to Beijing. Since then, a delegation of Chinese officers has visited military bases in Hawaii and Alaska, and another Chinese group visited Camp H.M. Smith to see how the Pacific Command handled administrative tasks.

A delegation of Pacific Command officers has visited China, while Fallon himself traveled there in May for a week of meetings and military installation tours.

Fallon said it was "a start" that China accepted his invitation to observe large-scale exercises the US military plans to hold off Guam next week.

"We take the step to invite them. There's an expectation that they will reciprocate," Fallon said.

The June 19-23 exercises will have three aircraft carriers operating together in the Pacific for the first time since the Vietnam War. Altogether some 30 ships, 280 aircraft, and 22,000 troops will participate in the drills.

Japan, South Korea, Singapore and Australia also plan to send observers to the exercises named "Valiant Shield."