Launching a campaign push billed as Operation Fightback by Labour headquarters, Brown sought in a televised speech to portray the Conservatives as elitist.
If you, like me, are from Britain's mainstream majority, from an ordinary family that wants to get on and not simply get by, then my message to you today is simple: take a second look at us, and take a long hard look at them, Brown said.
The Conservatives hit back that voters would reject Labour because of its performance during its 13 years in office.
He (Brown) asks Britain to take a second look at Labour when the public have been looking at them for 13 years and know they have failed, said top Conservative George Osborne, who is expected to become chancellor if his party wins.
Labour have won three elections since 1997 under the leadership of Brown's predecessor Tony Blair. Brown took over as prime minister when Blair stepped down in mid-term in 2007.
But Labour's star has faded since the financial crisis dragged Britain into recession. The Conservatives, led by the youthful and telegenic David Cameron, are far ahead in all opinion polls, although the gap has narrowed in recent weeks.
The election date is widely expected to be May 6.
Addressing a party rally on his birthday, Brown unveiled four key pledges for the campaign: to secure economic recovery, support new industries and future jobs, protect frontline public services and stand up for the many, not the few.I'M NOT PERFECT
Focussing on the economy is a risky strategy for Brown, who was chancellor for 10 years before he took over as prime minister, and thus is seen by many voters as partly to blame for a downturn that has cost hundreds of thousands of jobs.
Brown argues that his decisions at the height of the 2008 financial crisis averted a much bigger disaster.
In his speech, he said Labour would nurture a nascent recovery and rein in a ballooning budget deficit while also shielding schools, hospitals and the police from spending cuts.
Often criticised in his own camp for his stiff manner and his difficulty in connecting with voters, Brown has survived repeated leadership challenges. In an unusually relaxed performance on Saturday, he said he had changed.
I know -- really, I know -- that I'm not perfect, he said, smiling, to chuckles from an audience of party loyalists.
The moment was the latest in a series of comments apparently designed to soften Brown's image. He gave a television interview, broadcast last Sunday, during which he became tearful while talking about the 2002 death of his infant daughter.
In his speech, Brown also tried to come across as a fighter.
A key theme was that Labour stood for equality while the Conservatives represented the elite -- an attack on Cameron, who has promoted the idea of compassionate Conservatism.Brown sought to exploit recent Conservative gaffes, such as a mistaken claim in a party campaign document that 54 percent of teenage girls in Britain's poorest areas became pregnant before they turned 18. The correct figure is 5.4 percent.
Can they claim they know the aspirations of mainstream Britain when they so clearly understand so little of how we live? he said.
(Writing by Estelle Shirbon; editing by Andrew Roche)