Saturday, March 8, 2003; Page A01

A key piece of evidence linking Iraq to a nuclear weapons program appears to have been fabricated, the United Nations' chief nuclear inspector said yesterday in a report that called into question U.S. and British claims about Iraq's secret nuclear ambitions.

Documents that purportedly showed Iraqi officials shopping for uranium in Africa two years ago were deemed "not authentic" after careful scrutiny by U.N. and independent experts, Mohamed ElBaradei, director general of the International Atomic Energy Agency (IAEA), told the U.N. Security Council.

ElBaradei also rejected a key Bush administration claim -- made twice by the president in major speeches and repeated by Secretary of State Colin L. Powell yesterday -- that Iraq had tried to purchase high-strength aluminum tubes to use in centrifuges for uranium enrichment. Also, ElBaradei reported finding no evidence of banned weapons or nuclear material in an extensive sweep of Iraq using advanced radiation detectors.

"There is no indication of resumed nuclear activities," ElBaradei said.

Knowledgeable sources familiar with the forgery investigation described the faked evidence as a series of letters between Iraqi agents and officials in the central African nation of Niger. The documents had been given to the U.N. inspectors by Britain and reviewed extensively by U.S. intelligence. The forgers had made relatively crude errors that eventually gave them away -- including names and titles that did not match up with the individuals who held office at the time the letters were purportedly written, the officials said.

"We fell for it," said one U.S. official who reviewed the documents.

A spokesman for the IAEA said the agency did not blame either Britain or the United States for the forgery. The documents "were shared with us in good faith," he said.

The discovery was a further setback to U.S. and British efforts to convince reluctant U.N. Security Council members of the urgency of the threat posed by Iraq's weapons of mass destruction. Powell, in his statement to the Security Council Friday, acknowledged ElBaradei's findings but also cited "new information" suggesting that Iraq continues to try to get nuclear weapons components.

"It is not time to close the book on these tubes," a senior State Department official said, adding that Iraq was prohibited from importing sensitive parts, such as tubes, regardless of their planned use.

Iraqi President Saddam Hussein pursued an ambitious nuclear agenda throughout the 1970s and 1980s and launched a crash program to build a bomb in 1990 following his invasion of neighboring Kuwait. But Iraq's nuclear infrastructure was heavily damaged by allied bombing in 1991, and the country's known stocks of nuclear fuel and equipment were removed or destroyed during the U.N. inspections after the war.

However, Iraq never surrendered the blueprints for nuclear weapons, and kept key teams of nuclear scientists intact after U.N. inspectors were forced to leave in 1998. Despite international sanctions intended to block Iraq from obtaining weapons components, Western intelligence agencies and former weapons inspectors were convinced the Iraqi president had resumed his quest for the bomb in the late 1990s, citing defectors' stories and satellite images that showed new construction at facilities that were once part of Iraq's nuclear machinery.

Last September, the United States and Britain issued reports accusing Iraq of renewing its quest for nuclear weapons. In Britain's assessment, Iraq reportedly had "sought significant amounts of uranium from Africa, despite having no active civil nuclear program that could require it."

Separately, President Bush, in his speech to the U.N. Security Council on Sept. 12, said Iraq had made "several attempts to buy-high-strength aluminum tubes used to enrich uranium for nuclear weapons."

Doubts about both claims began to emerge shortly after U.N. inspectors returned to Iraq last November. In early December, the IAEA began an intensive investigation of the aluminum tubes, which Iraq had tried for two years to purchase by the tens of thousands from China and at least one other country. Certain types of high-strength aluminum tubes can be used to build centrifuges, which enrich uranium for nuclear weapons and commercial power plants.

By early January, the IAEA had reached a preliminary conclusion: The 81mm tubes sought by Iraq were "not directly suitable" for centrifuges, but appeared intended for use as conventional artillery rockets, as Iraq had claimed. The Bush administration, meanwhile, stuck to its original position while acknowledging disagreement among U.S. officials who had reviewed the evidence.

In his State of the Union address on Jan. 28, Bush said Iraq had "attempted to purchase high-strength aluminum tubes suitable for nuclear weapons production."

Last month, Powell likewise dismissed the IAEA's conclusions, telling U.N. leaders that Iraq would not have ordered tubes at such high prices and with such exacting performance ratings if intended for use as ordinary rockets. Powell specifically noted that Iraq had sought tubes that had been "anodized," or coated with a thin outer film -- a procedure that Powell said was required if the tubes were to be used in centrifuges.

ElBaradei's report yesterday all but ruled out the use of the tubes in a nuclear program. The IAEA chief said investigators had unearthed extensive records that backed up Iraq's explanation. The documents, which included blueprints, invoices and notes from meetings, detailed a 14-year struggle by Iraq to make 81mm conventional rockets that would perform well and resist corrosion. Successive failures led Iraqi officials to revise their standards and request increasingly higher and more expensive metals, ElBaradei said.

Moreover, further work by the IAEA's team of centrifuge experts -- two Americans, two Britons and a French citizen -- has reinforced the IAEA's conclusion that the tubes were ill suited for centrifuges. "It was highly unlikely that Iraq could have achieved the considerable redesign needed to use them in a revived centrifuge program," ElBaradei said.

A number of independent experts on uranium enrichment have sided with IAEA's conclusion that the tubes were at best ill suited for centrifuges. Several have said that the "anodized" features mentioned by Powell are actually a strong argument for use in rockets, not centrifuges, contrary to the administration's statement.

The Institute for Science and International Security, a Washington-based research organization that specializes in nuclear issues, reported yesterday that Powell's staff had been briefed about the implications of the anodized coatings before Powell's address to the Security Council last month. "Despite being presented with the falseness of this claim, the administration persists in making misleading arguments about the significance of the tubes," the institute's president, David Albright, wrote in the report.

Powell's spokesman said the secretary of state had consulted numerous experts and stood by his U.N. statement.