Iraq May Have Produced Enough Uranium for 2 Bombs : Weapons: Top priority for a U.N. team is locating a vintage nuclear enrichment system.

Bush Administration alarm over Iraq’s remaining nuclear capability centers on evidence that Baghdad retains key parts of a system that may have produced enough weapons-grade uranium for two nuclear devices, Administration sources said Friday.

Top priority for the U.N. nuclear inspection team now in Iraq is locating a 1940s-vintage uranium-enrichment system and seizing any material already turned out by the process, the sources said.

Since arriving in Iraq earlier this month, the U.N. team has used U.S. intelligence data to search for the hardware and uranium. U.S. intelligence officials learned in June that the older system had evaded detection and destruction by allied bombers.

Analysts said inspectors were searching for the hardware and enriched uranium when they were turned away at gunpoint from an Iraqi military base. An Administration source said the inspectors were looking for the same items Friday when they were turned away from a second site, and Iraqi soldiers fired guns in the air to keep them from taking photographs.

The older system employs a calutron, an electromagnetic apparatus for separating isotopes that was used in the Manhattan Project to develop the first atomic bomb. It is regarded as an inefficient but proven technique.

“We have no question whatsoever that they were able to salvage some of the calutron machinery,” said one Administration official. “The top priority is to try to get the Iraqis to declare and eliminate the machinery.”

This source said U.S. technical experts are skeptical that Iraq’s calutron system produced enough enriched uranium for a nuclear device. But other sources, including one in touch with the U.N. team, said 40 pounds or more may have been turned out.

Weapons-grade uranium is a critical component of a nuclear weapon. The amount needed depends on the design of the device, but experts say that 50 pounds could produce two bombs. If Iraq possesses secret quantities of the material, technicians could assemble one or more nuclear bombs.

Administration sources insist that Iraq does not retain a wholly working system for developing nuclear weapons. Rather, they said, key components of its nuclear facilities were dismantled before the Persian Gulf War began and hidden. Now, some parts are being moved around the country to evade the U.N. inspectors, and others are believed to be stored in mountain caves in northern Iraq.

The mystery uranium would be in addition to about 50 pounds of weapons-grade uranium that international authorities knew existed in Iraq before the Persian Gulf War. That material has been located and sealed in preparation for its removal from Iraq. But the Iraqis retain control of the material. Iraq has denied that it has any more enriched uranium.

The possible existence of the second batch of enriched uranium was disclosed to U.S. intelligence officials earlier this month by a defecting Iraqi nuclear scientist. The defector said he did not see the enriched uranium himself but said he was told that it existed.

However, the scientist said he did see the facility and calutron-based hardware believed to have been used to produce the material. U.S. officials said the defector’s information has been corroborated by other means.

“We don’t know if the hardware was used successfully before the war,” said Leonard S. Spector, a nuclear arms expert at the Carnegie Endowment for International Peace here. “If it was, there might be weapons-grade material in the hands of Iraq that we had never known about before. It is very important to get our hands on the hardware so we can make a judgment about this.”

If U.N. inspectors locate and remove all weapons-grade material and enriching machinery, Iraq would essentially have to start over to develop new material. Doing so would depend on a resumption of the virtually free flow of Western technology and technicians that helped build Iraq’s war machine in the 1980s. The United States and its allies have pledged not to repeat that process.

The system that supposedly produced the uranium relies on calutrons, offshoots of the early cyclotron invented by University of California Nobel Prize winner Ernest Lawrence. Electric power sources that could be used for calutrons were sold legally to Iraq by a U.S. firm in 1989, according to Nucleonics Week, a trade publication.

While the method is cruder than the gas centrifuge system that Iraq was also developing, it has at least one advantage. The existence of the centrifuge was well known because Iraq had purchased high-tech Western components for the system. The calutron system left a far fainter trail, said a source.

U.S. intelligence reports have indicated that components of Iraq’s nuclear program were hidden at military and civilian sites during the war and escaped destruction. Among the locations identified as likely hiding spots are caves in the mountains of northern Iraq.

“From our research, we had a pretty clear picture of everything they had gotten for their nuclear program before the war,” said one Pentagon official. “But they had time to move the most sensitive stuff.”

And some material that was not even moved survived. For instance, the 50 pounds of enriched uranium now under seal in Iraq was stored at the two nuclear-reactor sites near Baghdad that were destroyed by allied bombers. The uranium was undamaged.