WASHINGTON (Reuters) - The Bush administration should consider direct talks with North Korea amid signs that country may soon test a long-range missile, the chairman of the U.S. Senate Foreign Relations Committee said on Sunday.

The United States so far has refused direct discussions on a possible missile launch and instead has focused on six-way talks, involving the two Koreas, Japan, China and Russia, to convince Pyongyang to end its nuclear arms program in return for aid and security assurances.

"It would be advisable to bring out about a much greater intensification of diplomacy, and this may involve direct talks between the United States and the North Koreans," Sen. Richard Lugar (news, bio, voting record), a Republican, said on CBS" "Face the Nation" program.

The flurry of activity follows evidence that North Korea may test-fire a Taepodong-2 long-range ballistic missile that could reach the United States, which has activated a ground-based missile interceptor defense system.

"It would be very helpful if Russia and China were able to bring the pressure," Lugar of Indiana said. "But nevertheless, with regard to a missile that might have range to the United States, that becomes a very specific United States-North Korean issue, and perhaps Japanese-North Korean issue."

Such a test would be the first launch of a long-range missile since 1998, when North Korea surprised the world by shooting one over Japan that landed in the Pacific Ocean.

The United States has said firing a test missile would be inconsistent with a 1999 moratorium declared by North Korean leader Kim Jong-il, and which he reaffirmed in 2002.

Lugar advised the White House against taking a preemptive strike to take out the missile on the launchpad, though one Democrat said the option should be on the table.

"We can"t take anything off the table, and, of course, there are always sanctions short of military force," Sen. Barbara Boxer (news, bio, voting record), a California Democrat and member of the Foreign Relations Committee, said on the CBS program.

She also said she supported direct talks with North Korea.

The added pressure from Congress comes after the Senate last week approved an amendment to a defense authorization bill that would require the president to appoint a senior presidential envoy as a coordinator of U.S. policy on North Korea.

It must still pass the House of Representatives to become law.