Press secretary Tony Snow said releasing the full report, portions of which President Bush declassified on Tuesday, would jeopardize the lives of agents who gathered the information.
It would also risk the nation's ability to work with foreign governments and to keep secret its U.S. intelligence-gathering methods, Snow said, and "compromise the independence of people doing intelligence analysis."
"If they think their work is constantly going to be released to the public they are going to pull their punches," Snow said.
In the bleak National Intelligence Estimate, the government's top analysts concluded Iraq has become a "cause celebre" for jihadists, who are growing in number and geographic reach. If the trend continues, the analysts found, the risks to the U.S. interests at home and abroad will grow.
Peppered with questions Wednesday about the report, he said the NIE report was "not designed to draw judgments about success or failure, it's an intelligence document, it's a snapshot."
He said that a bleak intelligence assessment depicting a growing terrorist threat was only a "snapshot" — not a conclusion
The document has given both political parties new ammunition leading up to November's midterm elections.
For Republicans, the report provides more evidence that Iraq is central to the war on terrorism and can't be abandoned without giving jihadists a crucial victory.
For Democrats, the report furthers their argument that the 2003 Iraq invasion has inflamed anti-U.S. sentiments in the Muslim world and left the U.S. less safe. Democrats continued their push Wednesday for release of the rest of the report.
"The American people deserve the full story, not those parts of it that the Bush administration selects," said Sen. Edward M. Kennedy, D-Mass.
Rep. Peter Hoekstra, R-Mich., chairman of the House Intelligence Committee, warned, however, that releasing more of the intelligence assessment could aid terrorists. "We are very cautious and very restrained about the kind of information we want to give al Qaeda," Hoekstra said.
Defense Secretary Donald H. Rumsfeld, in Tirana, Albania for a meeting of defense ministers, said Mr. Bush had declassified the report's key judgments, after parts of it were leaked to the news media, so that "the American people and the world will be able to see the truth and precisely what that document says."