The Justice Department and CIA are not being fully cooperative with Congress' investigation into how the terrorists who carried out the Sept. 11 attacks escaped detection, the chairman of the Senate Intelligence Committee said Wednesday.

Some documents are not being turned over and interviews of potential witnesses are taking place in intimidating circumstances, Sen. Bob Graham, D-Fla., told reporters. He said committee officials intend to present their complaints personally to Attorney General John Ashcroft and CIA Director George J. Tenet.

"We thought we had from those highest levels the kind of assurances we would get cooperation," Graham said.

Justice Department and FBI officials could not be reached late Wednesday to respond to Graham's criticism. Graham acknowledged Justice officials told the committee that disclosing some documents could interfere with criminal investigations, but Graham said the committee regularly deals with classified materials and there's no chance those documents will be made public.

CIA spokesman Bill Harlow described the agency's cooperation with the investigation as "extensive, extraordinary and unprecedented."

"We've given them access to thousands of highly classified documents," he said. "We've given them briefings. We've given them information we have assembled, which, without our efforts, they would be unable to find. We've housed members of their staff in our headquarters. We've done all these things while we're fighting a war."

One official familiar with the investigation said some committee requests for information have required the compilation of hundreds of thousands of documents. But the investigation has uncovered no single missed piece of intelligence that would have allowed U.S. authorities to stop the attacks.

Graham said the committee may exercise its subpoena power to force cooperation.

Congress' investigation has hit other snags.

Its director, former CIA Inspector General L. Britt Snider, resigned after little more than two months on the job, apparently forced out over a personnel dispute with the Senate Intelligence Committee's vice chairman, Sen. Richard Shelby, R-Ala.

Graham acknowledged Snider's departure has caused some interruption in the investigation.

The tumult has forced back the beginning of public hearings on the issue, once promised to take place as early as April. They now won't begin before June.

The Democratic senator suggested the reluctance to cooperate reflected a tendency in the Bush administration, noting the administration's refusal to let Homeland Security Chief Tom Ridge testify to Congress and its resistance to turning over documents relating to its consultations on national energy policy.

Also Wednesday, Graham's committee passed a 2003 intelligence budget. Graham and committee officials declined to provide details. Shelby said it contained a "meaningful" increase in funding for the nation's intelligence community.

The war on terrorism has led to large spending increases for U.S. intelligence, as military and civilian agencies devote more resources to tracking and fighting Al Qaeda.

The total intelligence budget is kept secret, although open-government advocates last managed to get the government to disclose its total in 1998: $26.7 billion. Since, it has been estimated to be around $30 billion. The recent increases have probably pushed it closer to $35 billion or more.

Last year, the intelligence budget went up by about 8 percent. Officials said revitalizing the CIA's spy networks and improving the computers that analyze signals intelligence remain key goals in this year's budget.

This year, President Bush was believed to have proposed increasing the CIA's budget, which only makes up a portion of the total intelligence budget, from about $3.5 billion to between $5 billion and $5.5 billion for 2003.

Much of that would pay for expanding CIA's corps of overseas case officers, hiring allies and equipping counterterrorism teams in foreign countries averse to having U.S. military advisers on their soil.

Other intelligence agencies included in the budget are the National Security Agency, which conducts electronic wiretapping and signals gathering for foreign intelligence purposes; the National Reconnaissance Office, which designs and operates spy satellites; and the National Imagery and Mapping Agency, which interprets satellite imagery and makes military maps.