U.N. weapons inspectors, in a recent routine search of Iraqi missiles, discovered traces of the deadly VX nerve gas on warheads, a senior Clinton administration official disclosed Tuesday.

The discovery, to be detailed at the United Nations, will strengthen the hand of the United States in maintaining economic sanctions on Iraq when the issue is taken up by the Security Council on Thursday, said the official, insisting on anonymity."If this report is true, it will just show that our insistence over these last many years on the U.N. inspection system is the right thing to do for the safety of America and the safety of the world," President Clinton said Tuesday.

"We'll stay with the position we've always had: Let the inspections go forward, and don't lift the sanctions until the resolutions are complied with," Clinton said.

Similarly, in New York, Bill Richardson, the U.S. ambassador to the United Nations, said, "If this allegation is correct . . . that will set back Iraq's efforts to try to lift sanctions. It shows that they've been concealing, they've been lying, and it calls into question their commitment to disarmament."

Also in New York, diplomatic sources confirmed that Iraq had placed the nerve gas in its warheads, a development in missile power that Iraq consistently claimed it had failed to accomplish.

The sources said Richard Butler, chief of the U.N. inspection team, reported to the council last week that Iraq had been told about "the preliminary results of the chemical analysis of certain excavated remnants of special warheads."

"The Iraqi side rejected these results," the sources said. "Both sides agreed to continue further discussions on this issue."

In Baghdad, Deputy Prime Minister Tariq Aziz said Iraqi scientists had experimented with VX but were unable to turn it into a weapon.