Seeking to clarify confusion after surviving a parliamentary vote on the divisive issue on Tuesday, Blair said an inquiry now would send the wrong signals to both the fledgling Iraqi government and insurgents.
"We certainly do not rule out such an inquiry and we said in our own motion that lessons must of course be learnt and it's important always to do that," Blair said during his weekly question and answer session in parliament.
"But this is not the time for such decisions."
Blair's government came through the potentially damaging vote with a reduced majority on whether he should order an immediate inquiry into how Britain joined the US-led March 2003 invasion.
There was widespread confusion when Defence Secretary Des Browne said after the vote that the government would eventually hold a retrospective inquiry once the situation allowed.
Blair reiterated on Wednesday that an inquiry now would send a signal of weakness.
"Had that motion gone though last night it would have sent a signal that would have dismayed our coalition allies, it would have dismayed the Iraqi government and it would have heartened all those that are fighting us in Iraq," he said.
"That's why we opposed that motion and why it is important, frankly, that we stand up and we fight those in Iraq who are trying to prevent the democratic process taking root."

Copyright AFP (Agence France-Presse), 2006