Scuttlebutt has it that Defense Secretary Donald Rumsfeld and his new top Pacific brass, Adm. William Fallon, have been going at it hammer-and-tong over the depth and breadth of our relationship with China's military, the People's Liberation Army (PLA).

No element of the Sino-U.S. relationship is more fraught with complexity, danger and disagreement than defense issues. And while private disagreement/debate among senior officials can help flesh out good policy, there's no room for wishful thinking about Beijing's Pacific intentions and ambitions.

Adm. Fallon, the four-star Commander in Chief of the U.S. forces in the Pacific (CINCPAC), seems to think that "engaging" the PLA, including military-military meetings and visits/exchanges, will boost stability and enhance American security and other interests in Asia.

A Sino-U.S. "mil-mil" engagement program might include military academy/war college exchanges, senior officer/civilian expert meetings in Hawaii and Washington - and even joint U.S.-Chinese exercises such as peacekeeping or search and rescue missions.

CINCPAC seems to believe that failing to regularly communicate with his Chinese counterparts through "military diplomacy" is risky business, which could lead to miscalculation or misunderstanding - increasing the chance for conflict between his forces and the PLA.

Advocates of engagement say it can also help us gain insights into PLA capabilities, defense concepts and personalities; deter the use of force against Taiwan or other U.S. allies; and reduce the proliferation of weapons from China to North Korea, Iran and Pakistan.

Rumsfeld is much more skeptical of Chinese short- and long-term plans. (That he recently made his first trip to China in nearly five years as defense secretary should tell you something).

Think back to April 2001: Rummy had barely set up shop in the Pentagon when a Chinese fighter nearly splashed a Navy EP-3 plane over the South China Sea. The Chinese plundered the highly-classified aircraft for intelligence and held the crew for 11 days.

Insiders say the secretary sees the existing Sino-U.S. "mil-mil" relationship as overly advantageous to the Chinese - and chock full of risk of exposing U.S. strategic intentions, sensitive doctrine and cutting-edge capabilities to the PLA with little benefit to America.

One issue is China's lack of reciprocity. For example, while PLA delegations visit the Pentagon, China has yet to come through on standing U.S. requests for return trips to the PLA's equivalent HQ.

In addition, there is very little Chinese defense transparency. The secretive and deceptive PLA is very reluctant to let the Americans get a good look at Chinese military forces, doctrine and capabilities.

Even simple access is a problem. While our side gives PLA visitors exposure to real, active-duty U.S. troops and forces, Americans get trotted out to Chinese "show units" and meet with "barbarian handlers" (i.e., the PLA's political commissars and intel officers).

China keenly feels the U.S. technological edge in intel collection, and so uses exchanges with U.S. counterparts to gather information on American military practices and equipment, especially on high-value target vulnerabilities (e.g., aircraft carriers).

Back in the '90s, Congress decided that the Clinton Pentagon had grown too open in its handling of the "mil-mil" relations with China. To counter what it saw as PLA exploitation of U.S. naivete, it passed a law in 2000 cracking down. This prohibits "inappropriate exposure" to the PLA of certain U.S. military capabilities, including force projection, nuclear weapons, combined/joint operations, logistics and space operations.

The U.S.-China mil-mil relationship is a double-edged sword. Yes, there's reason to be skeptical - and cautious - about Chinese snooping, being sucked into an active disinformation campaign or lulled into complacency about China's rise.

Yet it promises real advantages for the American side, too. We can gather info, assess perceptions, understand the fitness and mettle of Chinese commanders and make our own intentions more clear - if, and only if, we get the access, reciprocity and transparency from the Chinese side.

Basically, we can't just rely on faith in the potential benefits. The defense relationship must advance/protect American security interests in the Pacific.

No one is looking to cross swords with the Chinese, but it might happen. Any mil-mil program with China must make us well-informed, clear-eyed and sober about the PLA.

Peter Brookes is a Heritage Foundation senior fellow. His book, "A Devil's Triangle: Terrorism, WMD and Rogue States," is just out