WASHINGTON - The same intelligence unit that produced a gloomy report in July about the prospect of growing instability in Iraq warned the Bush administration about the potential costly consequences of an American-led invasion two months before the war began, government officials said Monday.

The estimate came in two classified reports prepared for President Bush in January 2003 by the National Intelligence Council, an independent group that advises the director of central intelligence. The assessments predicted that an American-led invasion of Iraq would increase support for political Islam and would result in a deeply divided Iraqi society prone to violent internal conflict.

One of the reports also warned of a possible insurgency against the new Iraqi government or U.S.-led forces, saying that rogue elements from Saddam Hussein's government could work with existing terrorist groups or act independently to wage guerrilla warfare, the officials said. The assessments also said a war would increase sympathy across the Islamic world for some terrorist objectives, at least in the short run, the officials said.

The contents of the two assessments had not been previously disclosed. They were described by the officials after two weeks in which the White House has tried to minimize the council's latest report, which was prepared this summer and read by senior officials early this month.

Last week, Bush dismissed the latest intelligence reports, saying its authors were just guessing about the future, though he corrected himself later, calling it an estimate.

The assessments, meant to address the regional implications and internal challenges that Iraq would face after Hussein, said it was unlikely that Iraq would split apart after an American invasion, the officials said. But they said there was a significant chance that domestic groups would engage in violent internal conflict with one another unless an occupying force prevented them from doing so.

Senior White House officials, including Condoleezza Rice, the national security adviser, have contended that some of the early predictions provided to the White House by outside experts of what could go wrong in Iraq, including secular strife, have not come to pass. But Bush has acknowledged a miscalculation about the virulence of the insurgency that would rise against the country's American occupiers, though he insisted that was simply an outgrowth of the speed of the initial military victory in 2003.

The officials outlined the reports after Robert Novak, in a column published Monday in the Washington Post, wrote that a senior intelligence official had told a West Coast gathering last week that the White House had disregarded warnings from intelligence agencies that a war would intensify anti-American hostility in the Muslim world. Novak identified the official as Paul R. Pillar, the national intelligence officer for the Near East and South Asia, and criticized him for making remarks that Novak said were critical of the administration.

The National Intelligence Council is an independent group, made up of both outside academics and long-time intelligence professionals. Its main task is to produce National Intelligence Estimates, the most formal reports outlining the consensus of intelligence agencies. One of the intelligence documents described the building of democracy in Iraq as a long, difficult and potentially turbulent process with potential for backsliding into authoritarianism, the officials said.