With President Bush talking just weeks ago of the possibility of World War III if Iran developed a nuclear weapon, the newly-released National Intelligence Estimate (NIE) on the Iranian program this week is nothing if not a shocker.

You can't help but wonder what treasure trove of intelligence changed the Bush administration's mind. Because of the sensitivity of such things, we may never know. Until it's leaked, of course.

But while it's the seeming consensus of the 16-agency U.S. intelligence community that Iran "halted" its nuclear weapons program in the fall of 2003, there is no outside, independent verification.

There is still plenty of reason to worry about the current and future state of Iran's atomic ambitions.

First, the NIE confirms Iran had a nuclear weapons program, of "nuclear weapons design and weaponization work and covert uranium conversion-related and uranium-related work," separate from Iran's now-declared civilian nuclear program.

Way down in the two-plus page report, the NIE also mentions (almost as if to hide it) Iran's "considerable undeclared effort from at least the late 1980s to 2003 to develop such nuclear weapons."

If true, this would mean Iran violated the Nuclear Non-Proliferation Treaty (NPT), which obligates signatories to declare all of its nuclear activities as well as foreswear the pursuit of nuclear weapons.

In addition, the intelligence community is only "moderately" confident that as of mid-2007, Iran hadn't restarted its nuclear weapons program. Of course, a lot could have changed in the last six months.

Next, the NIE assesses "with moderate-to-high confidence that Tehran at a minimum is keeping open the option to develop nuclear weapons." This means Iran could decide to restart the program at any time. You can bet we won't be notified.

Indeed, the NIE judges the U.S. intelligence community doesn't have enough information to ascertain whether Iran will "maintain the halt" on the program indefinitely, or which criteria or deadlines would have to be met for Tehran to start it again.

Moreover, ignoring U.N. Security Council Resolutions calling upon Iran to cease uranium enrichment, the reprocessing continues. (Highly enriched uranium is a fundamental element in the production of nuclear weapons.)

Plus, Iran could easily develop uranium enrichment capability in the open, even complying with International Atomic Energy Agency inspection requirements while developing a parallel program for the clandestine production of fissile material.

For example, while lacking specificity, the NIE notes: "Iran has been conducting research and development projects with commercial and conventional military applications - some of which would also be of limited use for nuclear weapons."

More troubling, the report concludes - on its last line - that the intelligence community assesses with "high confidence" that Iran "has the scientific, technical and industrial capacity eventually to produce nuclear weapons if it decides to do so."

So the question remains whether the Iranian work stoppage is a short-term, tactical decision or a long-term strategic one.

While the NIE provides the basis for some (extremely) cautious optimism, it simultaneously reinforces the need for deep concern and continued vigilancce.

Peter Brookes is a Heritage Foundation senior fellow and former US deputy assistant secretary of defense.