Tony Blair says his party's next manifesto will be "unremittingly New Labour" and aimed at producing "personal prosperity for all".
Families have won under Labour, said Blair
The prime minister is trying to draw a line under speculation over the state of his relationship with Gordon Brown with the speech in Chatham, Kent.
He said that prosperity meant both individual wealth and ensuring "radically improved" public services.
He also claimed Labour was more ideologically united than ever.
Mr Brown is currently touring Africa after a week of questions about his alleged spat with Downing Street.
A new book by journalist Robert Peston fuelled speculation by claiming Mr Blair had gone back on a pledge to stand down as premier.
Mr Blair tried to put the focus on the substance of Labour's plans for a third term in government.
He insisted New Labour was not an electoral device but about making traditional values meet modern challenges.
The economy would be central to the election campaign, he said.
"I want to talk about the central purpose of New Labour - which is to increase personal prosperity and well-being, not just for a few but for all," he said.
"By prosperity I mean both the income and wealth of individuals and their families, and the opportunity and security available to them through radically improved public services and a reformed welfare state."
Mr Blair hailed Labour's record in cutting pensioner poverty, improving primary school standards and cutting waiting lists by 300,000.
But he said he was complacent neither about the "huge challenges" ahead nor on the election result.
Mr Blair said Labour had to earn a third term in power
"A third term needs to be earned," he said. "Life is tough for people as you solve one problem in government what you learn over time is that another one emerges."
So there were now legitimate worries about future pensions, truancy, hospital super bugs and gun and knife crime.
Mr Blair said voters faced a straight choice between New Labour's desire to extend prosperity and Conservatives "concerned only with a few at the top".
After the damaging talk of feuds, the prime minister heaped praise on Mr Brown achievements, calling him "the most successful British post-war chancellor".
The Tories are trying to capitalise on the apparent feud - the focus for their latest poster campaign.
Tory co-chairman Liam Fox said Mr Blair was asking people to believe he could finally deliver after eight years in office and 66 tax rises.
"But nothing he can say will be believable to the British public because they, like Gordon Brown, cannot trust a word he says," said Mr Fox.
Lib Dem Treasury spokesman Vince Cable said Labour complacency meant longer-term problems such as rising consumer debt and a spending deficits had been ignored.
"The prime minister should have put forward proposals on how things can be improved for pensioners and those on low-incomes, not spin and self-congratulation, said Mr Cable.