An independent inquiry into intelligence used to justify the UK's decision to go to war with Iraq is expected to be announced on Tuesday.
Blair insists the war was justified because Saddam posed a threat
President George Bush has announced he is to launch a similar probe in the US.
The Tories and Liberal Democrats have both called for an inquiry to be held into apparent intelligence failings.
No 10 has said a statement may be made to MPs on Tuesday on an inquiry seeking to answer "valid questions" about the failure to find WMD.
Mr Blair's official spokesman said there was a need to see how the lack of WMD compares with the intelligence ahead of the war.
He refused to give details of what form the inquiry might take, saying it would be spelled out to Parliament "shortly".
It had been suggested a formal announcement could take place on Monday although later that was ruled out prompting speculation there would be confirmation on Tuesday.
The delay is understood to have come about because of concerns of the Liberal Democrats about the remit of the inquiry which could not be resolved in time on Monday night.
Lib Dem leader Charles Kennedy is understood to have told Mr Blair during a phonecall he wants the inquiry to look not just at the intelligence, but on the political judgements of that intelligence which led to the war with Iraq.
Across the Atlantic President Bush announced the creation of an independent bipartisan commission of inquiry into the intelligence used on Iraq's alleged weapons of mass destruction in the run-up to war.
Mr Bush said it would look at "where we stand" and "what we could do better".
Pressure has grown since the former chief US weapons inspector, David Kay, said Iraq appeared to have no weapons of mass destruction.
Mr Blair will be questioned about intelligence when he makes his regular appearance at the influential Commons liaison committee of select committee chairmen on Tuesday.
On Wednesday, MPs will debate the Hutton report, which did not cover the strength of pre-war intelligence, and disappointed critics of the war.
Last week Downing Street said it would wait and see whether the Iraq Survey Group turned up evidence of WMD.
But Tory leader Michael Howard, said while he still believed the Iraq war was justified, an independent inquiry into the quality of intelligence presented before the conflict was now needed.
He told BBC Radio 4's Today: "I hope the prime minister won't continue to be the odd man out and... to be isolated on this."
Liberal Democrat foreign affairs spokesman Sir Menzies Campbell said news of the planned US inquiry would "put yet more pressure on the British Government".
"Washington is now dictating the British political agenda. The government's
satisfaction at the Hutton report may well be short-lived."
Commons leader Peter Hain said he had seen "categoric evidence"
that Saddam Hussein had chemical and biological WMD.
"I saw that intelligence, so did the prime minister, so did other Cabinet ministers," he told BBC One's Politics Show.