The sources said the aide made telephone calls to certain reporters on his own initiative, without instructions from Annan.

Clinton administration officials acknowledged Thursday that U.S. weapons experts, including some from intelligence agencies, helped U.N. inspectors search for Iraqi weapons. They said information gained during the inspections assisted U.S. military planners but flatly denied the intelligence agents acted as spies.

"The business of weapons of mass destruction arms control is extremely serious and cannot be carried out by amateurs," said State Department deputy spokesman James Foley. "The United States has sent UNSCOM (the U.N. Special Commission) our best weapons experts, both from the government and private organizations."

A former U.N. official told CNN that French and Russian intelligence agencies were also involved, "with the full knowledge of senior U.N. officials."

Administration officials have suspected Annan's aides leaked the story to undercut chief U.N. weapons inspector Richard Butler, whose aggressive style has led to sharp criticism from Baghdad. Administration officials fear Annan is trying to find a reason to replace the UNSCOM inspection team with a less intrusive body, one that would lack any U.S. involvement.

Butler said he expected "real answers" from a meeting with U.S. officials about Washington's involvement in the inspections operations, scheduled for Friday.

Butler denied his staff ever spied for the United States or Britain but said he wanted U.S. officials to clarify whether "some other collection efforts or piggybacking on us may have been taking place."

"We don't want our system misused in that way," he said.

U.N. and U.S. officials told CNN they did not know of any independent espionage work done by Americans while they were working for UNSCOM. They said U.S. intelligence learned about Iraqi leader Saddam Hussein's movements and security arrangements through "cooperation" with UNSCOM, but only as a "byproduct" of U.N. efforts to monitor programs for weapons of mass destruction.

The sources said the U.S. Central Intelligence Agency did help UNSCOM, at its request, to eavesdrop electronically on officers of special Republican Guard units assigned by Hussein to both conceal his illegal weapons programs and provide for the Iraqi leader's personal security.

Butler said he never authorized any surveillance of Hussein's communications -- only messages that related to the National Monitoring Directorate, which works with U.N. inspectors in searching for arms.

Concern at the United Nations that international inspections benefited U.S. intelligence threatens to undermine the basis for the Clinton administration's policy on Iraq. More than a year of tension between Washington and Baghdad began in the fall of 1997 when Iraq demanded an end to U.S. participation in the weapons inspections, charging that they were espionage operations. Iraq's lack of cooperation with the U.N. inspectors since then culminated in the pre-Christmas U.S. and British airstrikes on targets in Iraq.

David Ensor