He said opponents of centre-left policies were spreading the "myth" that the government caused the financial crisis and government spending was prolonging it.
And he accused them of "trying to use legitimate concerns about deficits to scare people into accepting a bleak and austere picture of the future for the majority".
Mr Brown added: "They seek to frighten us with the present level of the deficit but mention neither the automatic reduction that would be achieved as and when growth is resumed, nor the effects of growth on investor confidence for the good of the British people."
On Saturday, the Labour Party will launch its election slogan and themes, which will include a promise to secure the economic recovery.
The economists' letters have given Mr Brown a boost, but on Sunday, 20 other economists backed the Conservatives' call for cuts this year in a letter to the Sunday Times.
On Tuesday, Virgin boss Sir Richard Branson also called for spending cuts to begin this year - saying the UK budget deficit was a "serious risk" to economic recovery.
It's the lack of a plan of action from Gordon Brown that is undermining confidence in the British economy
George Osborne Shadow chancellor
The Tories say many business groups agree with them that the government lacks a credible plan to deal with the deficit, risking higher mortgage rates.
Mr Osborne said: "There are leading economists who support the Conservative position, but more importantly, there are also leading business organisations, top entrepreneurs - people like Richard Branson - who know more about creating jobs than the entire Labour cabinet put together.
"And people at home know that when you've got a debt problem then you have got to get on and deal with it and that is the key to the recovery."
He added: "It's the lack of a plan of action from Gordon Brown that is undermining confidence in the British economy."
Official figures out on Thursday showed the government borrowed another £4.3bn last month to plug the growing hole in the UK's finances.
It was the first time the government had borrowed money in January - usually a bumper month for income from tax receipts - since records began in 1993.
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