C.I.A. Said to Find North Korean Nuclear Advances

ASHINGTON, June 30 ・American intelligence officials now believe that North Korea is developing the technology to make nuclear warheads small enough to fit atop the country's growing arsenal of missiles, potentially putting Tokyo and American troops based in Japan at risk, according to officials who have received the intelligence reports.

In the assessment ・which they have shared with Japan, South Korea and other allies in recent weeks ・officials at the Central Intelligence Agency said American satellites had identified an advanced nuclear testing site in an area called Youngdoktong. At the site, equipment has been set up to test conventional explosives that, when detonated, could compress a plutonium core and set off a compact nuclear explosion.

Some intelligence officials say they believe that the existence of the testing range is evidence that North Korea intends to manufacture much more sophisticated weapons that would be light enough to put onto its growing arsenal of medium- and long-range missiles.

Previously, American officials had said they were uncertain whether North Korea had received enough outside technical help to even attempt the precision steps required to detonate such a "miniaturized" nuclear warhead.

The new testing capability does not mean North Korea can actually build a small weapon, but it suggests that the North Koreans are moving to combine their two most advanced weapons projects: nuclear technology and missile technology. The new intelligence reports suggest that they could develop such a weapon in less than a year, but some officials warn that that assessment represents what one called "a best guess rather than a solid estimate."

For months, Washington has been trying to convince Asian nations, especially South Korea and China, that the North Korean threat is so urgent that it requires a unified diplomatic front to force the country to give up its weapons. The new intelligence, officials who have seen it say, apparently is being marshaled to support the administration's argument.

According to officials who have been briefed on the American reports, conventional explosions simulating a nuclear detonation have been set off at the testing site, which is near North Korea's main nuclear complex. North Korea has never tested a nuclear weapon, though the C.I.A. long ago estimated that it manufactured two crude devices in the late 1980's or early 1990's.

North Korea, unlike Iraq, has made no secret of its plan to develop nuclear weapons. Now, administration officials say they fear that the North is on the verge of producing five or six new weapons, some of which might be miniaturized.

"This would give them the range they never had before, and the chance to spread their threat far beyond South Korea," said a senior Asian official, noting that about 60,000 American troops are based in Japan.

The new intelligence estimates provided to Asian allies, however, left it unclear how quickly the North could produce the small warheads. The worst-case estimate, officials say, is less than a year.

American satellites have watched North Korean nuclear activity intently since late last year, when the North evicted international inspectors. The inspectors had guarded a collection of 8,000 spent nuclear fuel rods, which can be reprocessed into weapons-grade plutonium.

In January, the North restarted its reprocessing equipment, which had been mothballed under a 1994 agreement with the Clinton administration. But according to American officials, it now appears that North Korean engineers ran into technical problems in restarting the program.

While intelligence officials have reached no consensus, they told allies last week that in the worst case, only a few hundred of the 8,000 rods had been converted into plutonium. It would take 1,000 to 1,500 rods to make enough plutonium for a weapon, experts say.

"What we are told is that it would take perhaps six months after that to produce a miniaturized warhead and put it into one of the missiles," said a senior official familiar with the intelligence. "But after Iraq, who knows how good those estimates are?"

After the claims made about prohibited weapons in Iraq, which have not been found so far, skepticism about the quality of American intelligence is widespread. And in the case of North Korea, as in Iraq, the immediacy of the threat depends on whose analysis seems most compelling.

So far, American intelligence has picked up almost no sign of the telltale krypton gas that is released into the atmosphere when nuclear fuel rods are converted into weapons-grade plutonium. That has led some analysts to argue that the North may be further from producing a weapon than feared a few months ago.

But others note that trucks were seen carrying the rods from their storage area months ago, and it is unclear where they are or whether the United States is sniffing for the krypton gas in the right place.

"We don't believe that the main reprocessing facility has been very active," a senior administration official said in a recent interview. "But could there be a second reprocessor? No one knows for sure."

Without question, though, North Korea's abilities greatly outstrip anything Iraq had in the last decade, and the North's program is probably several years ahead of Iran's.

President Bush and South Korea's president, Roh Moo Hyun, declared in mid-May that their two nations "will not tolerate nuclear weapons in North Korea." But it is unclear whether they interpret the meaning of that phrase the same way.

Mr. Bush has said he wants a diplomatic solution to the problem, but would not foreclose any option, including military options. Mr. Roh has said any pre-emptive strike against the North's nuclear facilities could prove disastrous.