The United States is looking for trilateral military cooperation with South Korea and Japan as it seeks to adjust to changing security environments, U.S. military commanders said Tuesday.

The United States will also seek to multinationalize the United Nations Command in South Korea by giving other member nations expanded roles, they said.

For South Korea, Adm. William Fallon, leader of the U.S. Pacific Command, urged the country to look beyond the peninsula in thinking about security as the two nations modernize their alliance.

"We also hope to foster greater trilateral military cooperation between the ROK, Japan and the U.S.," Fallon said at a Senate Armed Forces Committee hearing.

The United States has 30,000 troops stationed in South Korea, mainly to deter North Korea, which is believed to have weapons of mass destruction.

Testifying with Fallon, Gen. Burwell Bell, commander of U.S. Forces Korea, said the United Nations Command will also undergo some changes, mainly through involvement of other nations.

"It is the (U.N.) command"s intent to create a truly multinational staff by expanding the roles of the member nations and integrating them more fully into our contingency and operational planning and operations," the general said at the hearing.

Bell also pressed Seoul to pay more to maintain American forces in the nation, saying any shortfall would compromise their combat readiness. He also demanded better training facilities for his troops, especially shooting ranges.

Bell pointed to South Korea"s growing economic capacity and prominence and called for "a balanced defense burden sharing arrangement ... fundamental to the strength of the alliance."

North Korea is set to deploy ballistic missiles that could reach Alaska and remains a global security threat despite its failing economy, he said.

"Reports indicate North Korea is also preparing to field a new intermediate range ballistic missile which could easily reach United States facilities in Okinawa, Guam, and possibly Alaska," he told the Senate Armed Services Committee in Washington.

The leader of more than 30,000 U.S. troops in South Korea included the missiles among North Korean threats such as a huge conventional army, 100,000 special forces and 250 long range artillery systems that have Seoul, the South"s capital, within range.

Despite economic troubles that crimped its budget, "North Korea, through its "Military First" policy, has continued significant investment in asymmetric capabilities that include nuclear weapons programs, special operations forces, missiles, and weapons of mass destruction," Bell said.

The unconventional weapons include chemical weapons and a biological weapons research program, the general told the committee.

North Korea is working on a three stage version of its long range Taepo Dong missile, which could be operational in the next decade and would enable the country "to directly target the continental United States," Bell said.

North Korean leader Kim Jong il"s government remains committed to reunifying the Korean Peninsula under Kim"s control, Bell said, but added, "the ultimate goal of the North Korean dictator is self preservation."