Urenco's Enrichment Technology Company division develops, designs and builds centrifuges used in uranium enrichment, the most expensive part of nuclear energy production.

This alarming assessment was immediately challenged by the Energy Department, which builds centrifuges and runs the government's nuclear weapons complex.

Iraq, for instance, built centrifuges for enriching uranium with welding and milling machinery from Germany, lubricants from the U.S. and carbon fiber from Japan.

Mr. Stemmler worked until 1989 for Germany's M.A.N. Technologien G.m.b.H, which builds centrifuges for Europe's nuclear fuel consortium, Urenco.

From buying patterns, it was clear the Iraqis were building centrifuges based on the designs of a European consortium known as Urenco, including its models G-1, G-2 and G-3.

Another installation, Furat, closer to Baghdad, that was secretly building centrifuges for enriching uranium to weapons grade, was never hit.

Mr. Janetzki's old company, Janetzki G.m.b.H., has 180 workers who build centrifuges used in medical laboratories that do blood testing.

Beyond the question of stopping all enrichment, some officials and arms experts object even to letting Iran import, build and install centrifuges and parts, which would let it move toward its stated goal of completing 3,000 centrifuges by the year's end.

Whether Tehran and Washington can find any face-saving middle ground could depend on how quickly the Iranians move toward, or delay, what they say is the next phase: building new centrifuges, with the aim of installing nearly 1,000 by the end of this year.

In April, Iran disclosed that it was trying to build more advanced and powerful centrifuges known as model P-2, which would speed its enrichment program.