“New jihadist networks and cells, sometimes united by little more than their anti-Western agendas, are increasingly likely to emerge,” said Gen. Michael V. Hayden, during a speech in San Antonio in April, the month that the new estimate was completed. “If this trend continues, threats to the U.S. at home and abroad will become more diverse and that could lead to increasing attacks worldwide,” said the general, who was then Mr. Negroponte’s top deputy and is now director of the Central Intelligence Agency.

For more than two years, there has been tension between the Bush administration and American spy agencies over the violence in Iraq and the prospects for a stable democracy in the country. Some intelligence officials have said the White House has consistently presented a more optimistic picture of the situation in Iraq than justified by intelligence reports from the field.

Spy agencies usually produce several national intelligence estimates each year on a variety of subjects. The most controversial of these in recent years was an October 2002 document assessing Iraq’s illicit weapons programs. Several government investigations have discredited that report, and the intelligence community is overhauling how it analyzes data, largely as a result of those investigations.

The broad judgments of the new intelligence estimate are consistent with assessments of global terrorist threats by American allies and independent terrorism experts.