Mr Brown expressed determination to lead the country through difficult times
Gordon Brown has said it is "time to adapt and rethink New Labour" policy in response to new global challenges.
In an article for The Monitor, Mr Brown admitted people's chances in life had not improved as much as he would have liked and pledged to do more.
He said global and domestic pressures had changed and there was a "need to forge a new kind of government... to rise to conquer these challenges".
Aides said he did not mean changing his approach but the policies of the past.
In the article, Mr Brown, who has faced weeks of speculation about his performance as prime minister, said that long-term and short-term pressures had all changed since his party came to power in 1997.
"And so, the way we govern must change too. That is why in Manchester (where this year's party conference is) this year it is time to adapt and rethink New Labour policy," he wrote.
At a time of "profound change" in the global economy, technological development and population change, Britain was "well placed to withstand the shocks" but the government "must do more" to help seize opportunities, he said.
People must be equipped "for the inescapable challenges ahead" through education and training and helping people rise "as far as their talents can take them", he added.
"I want everyone in this country who works hard and plays by the rules to get their fair chance to benefit," he said.
The BBC's political editor Nick Robinson said Downing Street had been trying to play down the significance of Mr Brown's comments.
Aides said he was not about to adapt and rethink his own approach, but was instead saying, as he has on other occasions, that the policies of the past must be rethought and adapted to new challenges.
But for the Conservatives, Chris Grayling said Mr Brown had had 10 years to think about what he would do when he became prime minister, but now he was there had already changed his mind.
And Lib Dem frontbencher Danny Alexander said he had to prove himself "through action, not words".
Downing Street also dismissed claims that the prime minister had come out in favour of Democratic US presidential candidate Barack Obama - therefore breaking British convention.
In his article he praised Mr Obama's plans to help tackle the current credit crunch as part of a list of action by "progressive politicians" across the world. There was no mention of Republican candidate John McCain.
Downing Street said that Mr Brown was not backing one candidate over another but talking about the response from centre left parties around the world to the global economic crisis.
The prime minister has faced calls to improve his performance, with the party trailing the Conservatives by as much as 20% in the opinion polls.
Ahead of what could be a make-or-break speech to Labour delegates in Manchester later this month he also said he was determined to demonstrate he can provide the leadership needed.
"What I ask of our country, our government, and our party, cannot be done without leadership.
"So, at conference in Manchester and in the weeks that follow, I will set out how I - and our party, and our government, and our country - must rise to conquer those challenges and to ensure fairness for all," he said.
The prime minister acknowledged improvements in social mobility under Labour had not matched expectations: "We need to be honest with ourselves: while poverty has been reduced and the rise in inequality halted, social mobility has not improved in Britain as we would have wanted."