He is an expert at making centrifuges, hollow tubes that spin very fast to enrich natural uranium into bomb fuel.

The Russians put Dr. Zippe and other German prisoners of war to work making centrifuges to obtain the rare U-235 isotope.

Iraq used European designs for centrifuges in its earlier efforts, and American experts know what type of tubes are needed to make such centrifuges.

They say Iran would also want to convert uranium at Isfahan and to continue making centrifuges.

They also said it was the intelligence agencies' unanimous view that the type of tubes that Iraq has been seeking are used to make such centrifuges.

But making centrifuges is no easy trick.

Among the operations sold were companies that made centrifuges, Estes model rockets and Hi-Flier kites.

Presenting new information, he said that the United States has intercepted aluminum tubes that had a special coating that would make them useful for making centrifuges to enrich uranium.

After he secured a job in the Netherlands in the early 1970's at a plant making centrifuges - the devices that purify uranium - Dutch intelligence officials began watching him.

So the inspectors can no longer enter plants where Iran makes centrifuges and their numerous parts.