The Conservatives have called for a statement from Tony Blair on the future of UK involvement in Iraq.
The report may signal a change in US policy in Iraq
Following release of the Iraq Study Group report, Theresa May, the shadow Commons leader, demanded that Mr Blair address MPs on the issue.
She said the report was a "chilling commentary" on the management of war.
The report, by ex US Secretary of State James Baker, called the situation in Iraq "grave and deteriorating".
It also said the current US approach was "not working".
Mr Blair has returned from a visit to Washington, where he welcomed Mr Baker's report.
He said the people of the Middle East faced a choice - either secular or religious dictatorship, or "they can enjoy the same possibilities of democracy that we hold dear".
Ms May, speaking during business questions in the Commons on Thursday, said that the talks in the US between Mr Blair and President Bush would cover the government's response and the proposals for British involvement in Iraq in the future.
She asked for a statement on future UK involvement in Iraq to be made before the Christmas recess.
In response, Jack Straw, the Commons leader, said Mr Blair would be addressing concerns at a press conference in Washington.
Ms May expressed her disappointment and said the press conference was no substitute.
KEY SUGGESTIONS OF REPORT
Primary mission of US forces should evolve to one of supporting Iraqi army
By first quarter of 2008... all combat brigades not necessary for force protection could be out of Iraq
US must not make open-ended commitment to keep large numbers of American troops deployed in Iraq
Source: ISG report
Echoing her concerns, David Heath, for the Liberal Democrats, said a press conference was "not an appropriate response".
Addressing Mr Straw, Conservative MP Andrew Mackay said: "Can I ask you to pause and reflect that people out there realise that the report from the ISG is immensely important?"
He said the public would not understand why there had not been a response from the prime minister.
The Iraq Study Group report suggested a diplomatic offensive including talks with Iran and Syria.
Mr Blair has raised the possibility of discussion with Iraq's neighbours; something Washington has so far ruled out.
Following the Washington press conference, the BBC's diplomatic correspondent, Jonathan Marcus, said there was little sign Mr Blair and Mr Bush planned to shift their ground after the ISG review - with both sticking to their overall goals for Iraq and the Middle East.
The news came as Ministry of Defence figures revealed the conflicts in Iraq and Afghanistan would cost the UK £1.4bn this year - more than £3.8m a day. The war in Iraq is taking up £2.36m a day, or £860m a year.