North Korea (search) theoretically can mount a nuclear weapon on a long-range missile, a Pentagon spokesman said late Friday, providing more details than congressional testimony delivered a day earlier by a top intelligence official.

Defense Department (search) spokesman Bryan Whitman said the military has no evidence that the communist nation has actually put such a warhead atop a missile that could travel many thousands of miles.

If it can, it would mark a significant advance in Pyongyang's ability to threaten the United States at a time when the two countries are at a standoff over U.S. efforts to curtail North Korea's nuclear program.

On Thursday, Defense Intelligence Agency (search) chief Vice Adm. Lowell Jacoby told a Senate committee that North Korea can arm a missile with a nuclear device. He had left unclear, however, whether he was referring to a short- or long-range missile, nor did he specify whether he believed North Korea had already done so.

The Pentagon statement, issued Friday evening, marked its latest attempt to explain and in part soften Jacoby's testimony. It pointedly used the term "theoretical capability" to describe North Korea's capacity to produce a nuclear-armed missile. On Thursday, Jacoby had said he believed "they have the capability to do that."

"North Korea has a theoretical capability to produce a warhead and mate it with a missile, but we have no information to suggest they have done so," said the statement.

The finding is "based upon the fact that information concerning weapons design has been readily available for decades in unclassified literature, that North Korea has access to nuclear material and an assessment that North Korea has the capability to engineer a weapon based on those designs," the statement continued.

The U.S. intelligence community believes North Korea has one or more nuclear weapons, and has untested two- and three-stage missiles capable of reaching U.S. soil .

But it has been unclear whether Pyongyang has yet developed the technology to miniaturize a nuclear weapon so it fits on a missile, and provide it with the guidance systems so it can hit a target.

Pressed on the matter Friday, Lawrence Di Rita, the chief spokesman for Defense Secretary Donald H. Rumsfeld, said the United States does not know whether the North Koreans have a nuclear warhead small enough to be carried by a missile that could reach U.S. territory.

The Pentagon also said Jacoby's statement marked no new assessment, but simply restated remarks he made in March. Jacoby's previous statements, however, left unclear whether the U.S. believes the North Koreans had developed the necessary warhead technology.

Two defense officials said they believe it will be several years before North Korea can deploy an intercontinental ballistic missile with a nuclear warhead. They discussed the intelligence analysis Thursday on the condition of anonymity.

In the exchange Thursday, Jacoby was asked by Sen. Hillary Rodham Clinton, D-N.Y., whether "North Korea has the ability to arm a missile with a nuclear device?"

Jacoby answered, "My assessment is that they have the capability to do that."

Clinton called Jacoby's testimony "troubling beyond words."

U.S. intelligence believes a two-stage North Korean Taepo Dong 2 missile could hit Alaska, Hawaii and perhaps parts of the West Coast. North Korea also has shorter-range missiles which, some officials have said, may be able to carry a nuclear warhead as far as Japan.