If Iraq's weapons of mass destruction (search) posed enough of a threat to justify war, they should have been found by now, the top Democrat on the Senate Intelligence Committee (search) said Thursday.

Sen. Jay Rockefeller (search) of West Virginia challenged comments by Bush administration officials that the weapons were well-hidden and may not be located soon.

"You can't quite say that it's going to take a lot more time if the intelligence community seemed to be in general agreement that WMD was out there," Rockefeller said in an interview.

Rockefeller said that if the weapons were so well concealed, the United States should have considered giving U.N. inspectors more time to find them.

The Bush administration's main argument for the war was that Iraq possessed chemical and biological weapons and was possibly developing nuclear weapons. Those weapons threatened the region and, if given to terrorists, could be used against the United States, it said.

In recent weeks the administration has tried to diminish expectations that weapons will be found soon. Undersecretary of Defense Douglas Feith told a House committee May 15 that it "will take months, and perhaps years," for a complete account of Iraq's weapon programs to emerge.

Defense Secretary Donald H. Rumsfeld said Thursday, as he has before, that U.S. teams are unlikely to find any weapons of mass destruction unless Iraqis involved in the programs tell the officials where to look.

"It's not because they're not there. We do believe they are there," Rumsfeld said in an interview on the Infinity Broadcasting radio network. "We never believed that we or the inspectors would just trip over them."

In a speech Tuesday, Rumsfeld joined others who have been saying for a month that Iraq may have destroyed chemical and biological weapons before the war. On Thursday, Rumsfeld said there was "speculation and chatter" among intelligence agencies that such weapons may have been moved to other countries or buried.

Iraq also may have developed the capability to quickly make biological or chemical weapons, eliminating the need for storing large amounts of dangerous material, Rumsfeld said. Proof of that, he said, includes the two trailers found in northern Iraq which American intelligence officials say were mobile biological weapons production facilities.

Rockefeller said that, based on the intelligence he saw before the war, he was persuaded that Saddam Hussein had chemical and biological weapons. He said it is still possible "something may very well turn up."

White House spokesman Ari Fleischer Thursday called the two trailers "proof positive" that Iraq lied about not having mobile labs.

But Rockefeller said it's not enough to prove the weapons existed.

"In the business of WMD, and proving to the American people your case, you've got to come up with WMD. It's not happened," he said.

In a related matter, Rockefeller criticized the FBI response to his request for an investigation into forged documents used by the Bush administration as evidence against Saddam before the war. The documents indicated that Iraq tried to buy uranium from the West African nation of Niger.

He said the FBI sent a "bland" letter saying the forgery was not an administration attempt to manipulate public opinion, but offered no specifics. He said an aide told the FBI this was unacceptable and asked for more details.

FBI spokesman Bill Carter said the bureau was continuing to look at issues raised by Rockefeller and his staff. "We have not closed the book on this," he said.

Rockefeller and Intelligence Committee Chairman Pat Roberts, R-Kan., this week also requested that the State Department and CIA inspectors general investigate the forgery.

Rockefeller said either intelligence agencies hadn't detected the forgery, or they suspected the documents were forged, but may have faced political pressures to rethink that view.

"In either case, it's not a very happy outcome," he said.