The 1998 event turned out to be a space launch rather than a missile test; U.S. officials said the satellite failed to reach orbit.

U.S. and international concern about North Korea's missile capability is heightened by its claims to have developed nuclear weapons. It is not known whether they have mastered the complex art of building a nuclear warhead small enough to fit a long-range missile, although in April 2005 the director of the Defense Intelligence Agency, Vice Adm. Lowell Jacoby, told Congress that North Korea was capable of arming a missile with a nuclear warhead. U.S. officials have since called it a "theoretical capability."

No administration official has publicly raised the possibility of bombing the North Korean missile before it can be launched. Jan Lodel, a senior Pentagon policy official during the Clinton administration, said in an interview Tuesday that he would not rule out a pre-emptive strike. He said it would be the surest away of eliminating the threat of being surprised by the launch of a Taepodong-2, an intercontinental ballistic missile that some believe has enough range to reach U.S. territory.

David Wright, a senior scientist at the private Union of Concerned Scientists, said he strongly doubts that the Bush administration could back up its claims of having the capability to shoot down a North Korean missile.

"I consider it to be rhetorical posturing," Wright said. "It currently has no demonstrated capability."

The last time the Pentagon registered a successful test in intercepting a mock warhead in flight was in October 2002. Since then, there have been three unsuccessful attempted intercepts, most recently in February 2005.

Rick Lehner, chief spokesman for the Pentagon's Missile Defense Agency, said the next intercept test is scheduled for the August-September period, to be followed by another before the end of the year. Lehner said that beginning about a year ago, the system has periodically been placed in "operational status."

Baker Spring, a Heritage Foundation analyst and strong advocate of U.S. missile defenses, said he believes that "in theoretical terms" the U.S. system is a capable of defeating a North Korean missile. And he thinks that if the North Koreans launched on a flight pattern that appeared threatening to the United States, the administration "would be well within its rights" under international law to shoot down the missile.

The Washington Times reported Tuesday that the Pentagon has placed its missile defense system in an active status for potential use.