Although senior intelligence officials said they are convinced Iraq is hiding weapons of mass destruction, they feel they will not be able to prove it until after an invasion, when U.S. military forces and weapons analysts would have unrestricted access. These officials said the administration is withholding some of the best intelligence on suspected Iraqi weapons -- uncertain as it is -- from U.N. weapons inspectors in anticipation of war.

Sen. Carl M. Levin (D-Mich.), while chairman of the Armed Services Committee earlier this year, several times asked CIA Director George J. Tenet about how many of the "top suspect sites" had been passed to chief U.N. weapons inspector Hans Blix. The initial transfers of information to U.N. inspectors were limited as U.S. intelligence was measuring the security of Blix's system. In one early case, U.S. intelligence data had been electronically intercepted by Iraq, officials said.

Levin said in an interview that his concern the United States was holding back its best information was heightened by a March 6 letter Tenet sent to Sen. John W. Warner (R-Va.), now Armed Services Committee chairman. In it the CIA director said the United States has "now provided detailed information on all of the high-value and moderate-value sites," as well as "far more than half of these lower- interest sites" to the inspectors.