Better-than-expected tax and borrowing figures have given the Chancellor more leeway than anticipated – up to 12bn according to experts.
But despite the political pressure of a general election just weeks away, he insisted the focus would be on tackling the UK's record deficit.
"This will not be a giveaway Budget," he said, insisting the Government had to "continue to live within its means".
Among measures reported to be set for inclusion are a 1bn fund to kick-start investment in green transport and energy projects and extra help for the long-term unemployed.
Mr Darling is also thought to be considering whether to postpone a planned 3p rise in fuel duty.
He will use the Budget to confirm support for some form of global levy on banks if international agreement is reached.
However Tory leader David Cameron went further, promising to introduce such a measure unilaterally.
The Tories want to move faster on tackling the deficit, which the Government has pledged to halve in four years, but Labour insists that would "wreck" the recovery from recession.
In his weekly podcast, Prime Minister Gordon Brown warned: "We've reached a point in our economic recovery where we need decisions that will determine whether it takes root and we can go for growth – creating jobs and prosperity for all – or whether it withers and dies."Britain on borrowed time: