US Defense Secretary Donald H. Rumsfeld is hoping China will reveal more about its massive military, which the Bush administration sees as a potential near-term threat to US interests in Asia and a possible global rival in the future. Rumsfeld departs Monday on his first trip to China as defense secretary, marking a new opening to the country. China's military, with about 2.5 million people under arms, is the largest in the world, and Rumsfeld wants Beijing to provide more details about the scope of its budget and the intentions of its leaders. As a nod to the Americans, China agreed to allow Rumsfeld to visit 2nd Artillery Corps headquarters at Qinghe, which runs its strategic missile forces, but refused to enable his entry into the Western Hills command center. Rumsfeld would be the first US official ever to see the Qinghe headquarters, according to Pentagon officials speaking on condition of anonymity who briefed reporters on the trip.