Gordon Brown is set to urge voters not to risk the economic recovery with the Tories, as he seeks to shape the debate on public spending ahead of the next general election.
In a speech to the TUC conference in Liverpool, the Prime Minister will claim that the British economy is on the road to recovery - but will warn there is no room for complacency.
While continuing to insist that public services are safer in the hands of Labour than the Tories, it was reported that he would for the first time admit the need for spending "cuts".
His use of the word is expected to be seized on by the Tories, who have taunted Mr Brown over his refusal so far to acknowledge what many independent forecasters regard as inevitable.
Business Secretary Lord Mandelson said on Monday that Labour would reduce the country's massive debts by being "wise spenders". He said the Conservatives, by contrast, would impose "savage" cuts on services and were "foaming at the mouth" at the prospect of spending less on the NHS and schools.
Lord Mandelson insisted that it was too early to start reducing the £175 billion deficit now, warning that Tory plans to rein in spending immediately risked "triggering an economic relapse" before Britain has recovered from recession.
"While the freefall in the economy may have been brought to an end, the effects of the recession are not yet behind us," he warned. "This is why maintaining Government spending and investment is vital."
Mr Brown is expected to send a similar message to union leaders in Liverpool as he embarks on his last conference season before the next general election.
According to extracts from his speech that emerged at the weekend, he was to say: "Today we are on a road towards recovery - but things are still fragile, not automatic, and the recovery needs to be nurtured.
"People's livelihoods and homes and savings are still hanging in the balance, and so today I say to you: don't put the recovery at risk. Don't risk it with the Tories whose obsessive anti-state ideology means they can't see a role for government in either recession or recovery."