Nuclear experts yesterday questioned a decision by the Energy Department to leave in Iraq nearly 400 tons of natural uranium that could be enriched for a nuclear weapon or used to build a radioactive "dirty bomb."

On Tuesday, Energy Secretary Spencer Abraham announced that about two tons of low-enriched uranium and about 1,000 radioactive sources had recently been removed from an old Iraqi nuclear facility and brought to the United States for safety reasons.

Although low-enriched uranium can be made usable for a bomb much faster, the "natural uranium is still dangerous and could be used in a nuclear weapons program or sold to somebody that would misuse it," said David Albright, a nuclear analyst and former weapons inspector in Iraq.

Bryan Wilkes, spokesman for the National Nuclear Security Administration, said yesterday that the natural uranium is not considered an immediate proliferation concern and is being stored under the authority of the interim Iraqi government in a protected location.

The decision to remove the more dangerous materials was made by the National Security Council nearly one year after the invasion. The operation was completed on June 23, several days before the United States transferred political authority to the Iraqis.

"They lost a real opportunity to move the natural uranium, and that's disappointing since they had well over a year to do it when the country was exclusively under American control," Albright said. "We have no idea what Iraq will look like in a year."

The International Atomic Energy Agency kept Iraq's uranium under seal in storage facilities for more than a decade before the U.S. invasion in March 2003, but the storerooms were looted when Baghdad fell several weeks later.

The IAEA was allowed back into Iraq to help clean up the facility, and it urged U.S. officials to protect Iraq's former weapons sites from further looting.

But in recent months, radioactive equipment and Iraqi weapons components have been showing up in scrap yards and ports in Europe and the Middle East.

Mohamed ElBaradei, the director general of the IAEA, has unsuccessfully lobbied the White House to let international inspectors return to Iraq. He is now discussing the matter with Iraqi authorities. Before the war, ElBaradei reported that Iraq had no nuclear weapons program, despite assertions to the contrary by the Bush administration, which went to war to remove weapons of mass destruction. Such weapons have not been found.

In a letter to the U.N. Security Council yesterday, ElBaradei said the IAEA had been told about the operation to remove the low-grade uranium and radiological sources, but he made it clear that the international nuclear agency -- which has a mandate to oversee Iraq's nuclear materials -- was not consulted or asked to participate.