The US suggested Thursday it has limited ability to shoot a North Korean missile out of the sky and spurned suggestions of a pre-emptive strike on the ground. Still, it warned the Koreans would pay a cost for a missile launch.

A commercial satellite photo of North Korea's Nodong missile launch site taken on by a Digital Globe satellite and annotated and released by analysts at GlobalSecurity.org on May 24, 2006.  [Reuters]

The nation's missile defense system, which now includes about a dozen interceptor missiles in Alaska and California and on some Navy ships, has suffered multiple test failures since US President Bush ordered the Reagan-era program accelerated in early 2001.

Missile defense experts disagree on current US ability to destroy a long-range missile once it is fired. But they seemed in agreement that shooting at it, and missing, would be a huge embarrassment.

A better solution, said Bush's national security adviser, Stephen Hadley, was for the North Koreans to "give it up and not launch" the missile that the US believes is being fueled and prepared. "We think diplomacy is the right answer and that is what we are pursuing," he said.

Tensions persisted over North Korea's apparent preparations to test-fire a Taepodong-2 missile amid disagreements over US military options for responding. The missile, with a believed range of up to 9,300 miles, is potentially capable of reaching the mainland United States.

Pentagon officials said they were prepared to use the nation's missile defense system if needed.

Asked under what circumstances it would be used against a North Korean missile, Defense Secretary Donald H. Rumsfeld said Thursday, "The president would make a decision with respect to the nature of the launch, whether it was threatening to the territory of the United States or not, and the likely threat that it would pose."

Rumsfeld expressed no sense of alarm about the missile situation. "It's clear: All the intelligence suggests they have been making preparations for a launch of a missile from the area of Taepo Dong for some days now. There's a lot we know and a lot we don't know. So we'll just have to see."

The USS Abraham Lincoln, USS Kitty Hawk and USS Ronald Reagan carrier strike groups steam in formation during a joint photo exercise (PHOTOEX) in preparation for Valiant Shield 2006 on Sunday, June 18, 2006, in the Pacific Ocean. This is one of the largest US military exercises in decades off Guam in the Pacific. [AP]

The US missile defense program is a downscaled land-and-sea version of a global defense network first proposed by Reagan that was dubbed "Star Wars" by critics. Interceptor missiles, linked to a network of satellites, radar, computers and command centers, are designed to strike and destroy incoming ballistic missiles.

The Pentagon says the system is capable of defending against a limited number of missiles in an emergency, such as a North Korean attack. More than $100 billion has been spent on the program since 1983, including $7.8 billion authorized for the current fiscal year.

In the most recent test, a Navy ship late last month successfully shot down a long-range missile in its final seconds of flight. Before a successful test in the Pacific in December 2005, interceptor tests had failed five of 11 times.

In developments Thursday:

-- William Perry, a Clinton administration defense secretary, advocated a strike on the missile on its launch pad. "Diplomacy has failed, and we cannot sit by and let this deadly threat mature," Perry and former assistant defense secretary Ashton B. Carter wrote in Thursday's Washington Post.

-- US Vice President Dick Cheney said North Korea's "missile capabilities are fairly rudimentary" but developments were being closely monitored. In a CNN interview, Cheney rejected Perry's suggestion of a pre-emptive strike, saying, "The issue is being addressed appropriately."

-- Peter Rodman, assistant secretary of defense for international security affairs, said Pyongyang risks unspecified retaliation in proceeding. "If such a launch takes place, we would seek to impose some cost on North Korea," Rodman told the House Armed Services Committee.

-- Loren Thompson, a defense consultant at the Lexington Institute in Arlington, Va., cited "two basic problems" with trying to shoot down a Korean missile in the air. "Our system is barely operational. And the impact on Korean perceptions if we miss could be counterproductive."

-- Ivo Daalder, a former Clinton national security aide now at the Brookings Institution said: "Either it won't work, in which case you've just undermined the rationale for the system. Or if it does work, you have created an even bigger international crisis."

Hadley brushed aside Perry's suggestion for a pre-emptive strike. Instead, he said, "We hope it (North Korea) would come back to the table, and we hope it would be a little sobered by the unanimous message that the international community has sent."

No international talks to persuade North Korea to restrict its nuclear program have been held since last November. The five other nations in the talks, the US, China, Russia, Japan and South Korea, have all strongly urged the North not to launch the missile.

Hadley, who briefed reporters in Budapest, Hungary, during a Bush visit, expressed some reservations about the US ability to intercept and destroy such a missile: "It is a research development and testing capability that has some limited operational capability."

"If the North Koreans fire the missile and the president chooses to launch an interceptor, the administration has an odd set of options," said Daryl Kimball, executive director of the private Arms Control Association.

"If it hits the missile, will the North Koreans consider that an act of war? And if the interceptor misses the North Korean test missile, it would simply illustrate the fact that we spent tens of billions of dollars for a system that's not effective, even against one missile from one known launch point."