A report on US policy in Iraq is to urge negotiations with Iran and Syria over the future of their neighbour, according to leaked excerpts.
The report is expected to recommend a phased withdrawal
US President George W Bush has said the Iraq Study Group (ISG) report will be taken "very seriously" and has promised to "act in a timely fashion" on it.
US broadcaster ABC says the report, to be made public later, stops short of a firm timetable for troop pullout.
Washington has so far refused to hold direct talks with Iran and Syria.
Speaking after meeting ISG members for about an hour, Mr Bush said their report gave "a tough assessment" of the situation in Iraq.
"It is a report that brings some really very interesting proposals, and we will take every proposal seriously and we will act in a timely fashion," he said.
According to ABC News, the ISG makes 79 recommendations in its long-awaited 142-page report.
The leaked extracts confirm what many expected, says the BBC's James Westhead in Washington.
US must not make open-ended commitments to keeping large numbers of troops in Iraq
Primary mission of US forces should evolve to one of supporting Iraqi army
All combat troops could leave Iraq by the first quarter of 2008
Source: ABC News
According to ABC, the report calls for "a new diplomatic offensive to build stability in Iraq", including direct talks with Iran and Syria - something President Bush has so far set strict conditions on.
Speaking ahead of the report, Syria has repeated its willingness to co-operate with the US.
Information Minister Mohsen Bilal said it was in Syria's interest to help Iraq, and that his country had had interesting discussions with members of the ISG.
The BBC's Jon Leyne in Damascus says the Syrian government sees developments in Washington as an opportunity to come out of international isolation.
The ISG had also been expected to recommend a gradual phased withdrawal of US troops over the next 18 months.
According to the leaks, the report will back a reduction in the number of US troops in Iraq - perhaps halving it from the current level of 140,000 - as well as changing the nature of their engagement from a combat to a back-up role.
"The primary mission of US forces should evolve to one of supporting the Iraqi army," ABC News quotes the report as saying.
The report suggests there should be an initial increase in the number of US troops dedicated to supporting Iraqi troops, ABC says, but does not specify whether this will mean an increase in overall US troop numbers before they start falling.
The report ends with a plea for a broad political consensus, predicting that without it US foreign policy is doomed to failure.
Mr Bush has previously indicated he will look closely at, but not necessarily follow, the suggestions of the group, which headed by former Secretary of State James Baker.
The 10-member panel of influential former policy-makers and practitioners of international affairs has been working since April to come up with recommendations.
The ISG has met or spoken to more than 170 individuals, including Iraq's leaders, President Bush, UK Prime Minister Tony Blair, ambassadors and other senior officials from among Iraq's neighbours and the US.
Hundreds of others have fed their suggestions to four working groups, which have written analytical papers for the panel's benefit.
Mr Blair arrived in Washington on Wednesday for a visit which will include meetings with President Bush and congressional leaders.