Tony Blair has suggested that Gordon Brown would remain as chancellor if Labour won a third term in power.
There has been intense speculation over a Blair-Brown rift
He was the best chancellor for 100 years, Mr Blair said, adding: "It would be pretty foolish to put that at risk."
Mr Blair said Tory spending plans did not add up and would risk everything Labour had worked so hard to create.
The Conservatives say taxes will have to rise if Labour are re-elected, while the Lib Dems say Mr Brown has failed to make the current tax system fairer.
At the party's first official election campaign press conference, Mr Blair's attempt to focus on the economy was repeatedly derailed as reporters persisted with questions about Mr Brown's future.
He was pressed over when exactly he planned to step down as prime minister and whom he would endorse to take over from him.
There have been reports that the prime minister is planning to move Mr Brown from his job at the Treasury, especially if he secures a large majority.
And in earlier interviews he has refused to speculate about what job the chancellor might perform in the future.
Mr Blair said the present economic stability was "the absolute bedrock" of everything Labour wanted and needed to achieve and accused the Tories of wishing to dodge the subject.
This was because of their record and because their sums did not add up, he said.
Mr Blair said: "The Tories used to run on the economy in any election but now they are running from it.
"That used to be the number one place for them in the battleground in any election. Now they have vacated it.
"It's our task to make sure they can't do that."
The chancellor challenged reporters to look at the detail of the Tory economic plans and said they had opposed the 10 key measures that had created economic stability in Britain.
The Tories have denied they would put the economy at risk and say taxes will have to rise under Labour to fill a multi-million black hole in the chancellor's finances.
Shadow Chancellor Oliver Letwin said it was Mr Blair who did not want "talk about the truth".
"He certainly doesn't want to talk about the official figures since the Budget showing the first fall in incomes for a decade, the biggest monthly fall in house prices for a decade, the worst retail sales since 1992 and personal debt hitting record levels."
The Lib Dems say Mr Brown has missed the opportunity to make the tax system fairer.
They are planning to scrap the council tax and replace it with a local tax based on earnings. They also want to raise tax rates for the top 1% of earners.
Labour also announced plans to give tax breaks worth up to £50 a week for parents paying for child care.