Despite the Bush administration's claims about Iraq's weapons of mass destruction, U.S. intelligence agencies have been unable to give Congress or the Pentagon specific information about the amounts of banned weapons or where they are hidden, according to administration officials and members of Congress.

Senior intelligence analysts say they feel caught between the demands from White House, Pentagon and other government policymakers for intelligence that would make the administration's case "and what they say is a lack of hard facts," one official said.

"They have only circumstantial evidence . . . nothing that proves this amount or that," said an individual who has regularly been briefed by the CIA.

The assertions, coming on the eve of a possible decision by President Bush to go to war against Iraq, have raised concerns among some members of the intelligence community about whether administration officials have exaggerated intelligence in a desire to convince the American public and foreign governments that Iraq is violating United Nations prohibitions against chemical, biological, or nuclear weapons and long-range missile systems.

"They see a particular truck associated with chemical weapons activities keep reappearing, and they estimate chemical activities are there, but that and most intelligence would not pass the courtroom evidence test. For policymakers, who are out on a limb, that is not enough," one official said, adding that he questioned whether the administration is shaping intelligence for political purposes.

Said another senior intelligence analyst, "If it walks like a duck, quacks like a duck and looks like a duck, we professionals say it's a duck. . . . They [policymakers] want a smoking duck."

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.

"They are clearly hiding weapons, but it is a Catch-22 situation that we will only prove after an invasion," one senior intelligence official said.

U.S. intelligence on Iraqi weapons sites has raised a credibility problem involving the U.N. inspectors and, more recently, members of Congress.

Intelligence agencies in December produced a 2-inch-thick book that listed high- , medium- and low-priority sites in Iraq related to weapons of mass destruction, according to senior administration officials and members of Congress.

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 was concerned that only a small number of sites contained in the December list had gone to Blix's team, but at a public hearing in February, Tenet said that all relevant information on high- and moderate-value sites had been shared with the inspectors.

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.

Levin wrote Tenet back March 7 saying the CIA director gave a "misleading assertion" and repeated a request that Tenet provide a percentage figure, not the number, of the "top suspect sites" listed in the December report that had been turned over to U.N. inspectors. "I can't believe we are holding back, and it would be shocking if it is being done, because it might lead the inspectors to something," Levin said.

A CIA spokesman refused to discuss the matter. But some officials charge the administration is not interested in helping the inspectors discover weapons because a discovery could bolster supporters in the U.N. Security Council of continued inspections and undermine the administration's case for war.

"We don't want to have a smoking gun," a ranking administration official said recently. He added, "I don't know whether the point is to embarrass Blix or embarrass Saddam Hussein."

Anther official familiar with the intelligence said, "Not all the top sites have been passed to the inspectors."

A senior intelligence analyst said one explanation for the difficulties inspectors have had in locating weapons caches "is because there may not be much of a stockpile."

Administration officials, in making the case against Iraq, repeatedly have failed to mention the considerable amount of documented weapons destruction that took place in Iraq between 1991 and 1998, when the previous U.N. Special Commission on Iraq had inspection teams in the field.

In that period, under U.N. supervision, Iraq destroyed 817 of 819 proscribed medium-range missiles, 14 launchers, 9 trailers and 56 fixed missile-launch sites. It also destroyed 73 of 75 chemical or biological warheads and 163 warheads for conventional explosives.

U.N. inspectors also supervised destruction of 88,000 filled and unfilled chemical munitions, more than 600 tons of weaponized and bulk chemical weapons agents, 4,000 tons of precursor chemicals and 980 pieces of equipment considered key to production of such weapons.

Destruction of biological weapons -- which were not discovered to be in Iraq's possession until 1995 -- was less advanced. The main facility where biological weapons were produced and developed, Al Hakam, was destroyed along with 60 pieces of equipment taken from three other facilities. In addition, 22 tons of growth media for biological weapons were destroyed.

Staff writer Bob Woodward contributed to this report.

Sen. Carl M. Levin (D-Mich.) says withholding data from inspectors in Iraq "would be shocking."