The Prime Minister urged voters to go behind the "gloss and the posters and the PR and the style" and see that Conservatives were planning an "assault on all the pillars of the welfare state".
He called on Labour activists to go out and "fight and fight and fight again" for a fourth term.
During Mr Brown's speech to young supporters at Westminster Academy in west London he pointed to David Cameron's interview with Jeremy Paxman on Friday, in which the Tory leader indicated public sector cuts would hit Northern Ireland and the North East first.
"They have Sunderland in their sights, Hartlepool, Redcar, Durham," Mr Brown warned.
"There will be new cuts in Newcastle, Middlesbrough, Morpeth – and what begins with the towns and cities of the North East will not end there, but will set the blueprint for their attacks on jobs and investment not just in the North East but in the North West, and the Midlands, in Yorkshire and the Humber, coming towards London too.
The Tories were "hurting not just modest income Britain but middle income Britain", he said.
"For once you go behind the gloss and the posters and the PR and the style you find that policy by policy, detail by detail, the Tories are planning an assault on all the pillars of the welfare state."
Only a Labour government could deliver fairness for all, Mr Brown said.
"If you believe in fairness you need to fight for it because a fairer future doesn't happen by chance.
"Get out and fight and fight and fight again, not for our party's future but fight for our country's future.
"Fairness is in our DNA, fairness is in the British people's DNA. We are fighting an election for the British people. Let's fight it and let's win it."
The Prime Minister's rallying speech came as Labour launched its green manifesto, including commitments to create 5,000 low carbon apprenticeships and help those on low incomes with their energy bills.
Mr Brown promised all pensioners over 75 in receipt of pension credits would receive a further 100 off their bills, on top of the winter fuel allowance.
And he warned that although the Conservatives had tried to improve their environmental image, the "green gloss" had peeled off to reveal they had not changed at all.
He highlighted his plans for referendums on electoral reform for the House of Commons and the creation of an elected House of Lords and said no democratic country could justify having hereditary peers in the House of Lords.