WASHINGTON - Despite its threat of severe consequences, the Bush administration has little leverage to use on North Korea to keep it from testing a long-range missile and few ways to punish the nuclear-armed nation if it proceeds.

The United States has no diplomatic or economic ties with North Korea, the rudimentary U.S. missile-defense system is untested in real-world conditions and Pyongyang is regarded as having a right to test missiles, making any American attack to forestall a launch an act of war with potentially explosive consequences.

"The United States could try to shoot down the rocket, but good luck,'' said Wonhyuk Lim of the Brookings Institution, a policy-research organization in Washington.

The dearth of options illustrates the limits of the administration's pre-emption strategy and its need to rely on the cooperation of others -- especially given the strains on the U.S. military from Iraq and Afghanistan -- to contain threats.

Washington hopes that the world's only Stalinist regime will heed demands by the United States, South Korea, Japan, Russia and China to uphold a self-imposed 1999 moratorium on missile tests and rejoin talks on curbing its nuclear program in return for security guarantees and economic and political benefits.

At the same time, the administration is reviewing its options should the Kim Jong Il regime test-fire what U.S. officials describe as a multi-stage Taepodong-2 missile, thought to be capable of reaching Alaska.

"The launch of a missile would be a provocation,'' Assistant Secretary of Defense Peter Rodman said Thursday during a House Armed Services Committee hearing. "If such a launch took place, we would seek to impose some cost on North Korea.''

Rodman declined to say what Washington would do. Experts said that even the imposition of sanctions by the United States would be largely symbolic.

They think that North Korea would not have readied the missile for flight unless it had decided it could live with the consequences.

"It probably means they are not worried about the American reaction,'' said Daniel C. Sneider of Stanford University's Shorenstein Asia-Pacific Research Center. "There is nothing that the United States can do to them.''

The United States has no diplomatic relations or financial assistance it can threaten to cut, and it suspended contributions to international food aid for North Korea last year.

The administration has moved against Pyongyang by trying to halt its missile sales to other countries, its alleged international narcotics trafficking, and its alleged counterfeiting of U.S. currency, cigarettes and over-the-counter drugs.

Under American pressure, banking regulators in February froze North Korean accounts at the Banco Delta Asia, a Macao bank that the U.S. Treasury Department accused of laundering North Korea's ill-gotten gains.

Other banks, anxious to avoid American scrutiny, reportedly have curtailed business with North Korea.

David L. Asher, a former Treasury Department official who oversaw the crackdown on North Korea's alleged illicit dealings, said the United States could respond to a test with an intensified campaign against Pyongyang's alleged international criminal activities that would hurt the ruling elite.

"Do not underestimate the impact of the financial pressure we could put on them,'' said Asher, a scholar with the Institute for Defense Analyses, a policy-research organization.

Washington is counting on Japan, which also is threatened by Pyongyang's nuclear arms and missile programs, to react to a launch by closing ports to North Korean ships and shutting off remittances by ethnic Koreans to relatives in North Korea. But those measures are expected to have limited impact.

A North Korean missile test in 1998 prompted Japan to boost missile-defense cooperation with the United States, and experts said a new launch probably would prompt Washington and Tokyo to forge even closer military ties.

The only nations that could tighten the screws significantly are China and South Korea, North Korea's main foreign trading partners and aid donors.

But while Seoul and Beijing would be outraged, because a missile test would effectively kill hopes of restarting talks on containing North Korea's nuclear arms program, they are unlikely to take any step that could rock Pyongyang.

Both are anxious to avoid destabilizing their neighbor of 26 million people. China doesn't want to be overwhelmed by North Korean refugees, and South Korea would be unable to bear the economic and social costs of sudden reunification.

They also fear that Kim's government could lash out with its million-member army against the South, igniting a conflict that would drag in the United States and devastate the Asian-Pacific economy.

"China and South Korea fear instability more than they fear a nuclear North Korea,'' said Marcus Noland, an expert at the Economic Policy Institute.

Moreover, Beijing probably would be unwilling to jeopardize the budding commercial ties it has been pursuing with North Korea.

"China opposes sanctions on North Korea because it believes they would lead to instability, would not dislodge the regime but would damage the nascent process of market reforms and harm the most vulnerable,'' said a February report by the International Crisis Group, a conflict-prevention organization.

South Korea has been pursuing a policy of economic engagement and political exchanges with North Korea.

The United States has been consulting with members of the U.N. Security Council on a response to a North Korean test. But North Korea has the right under international law to test-fire missiles, making it tough for the United States to win more than words of chastisement of North Korea from the council.