Lib Dem leader Nick Clegg insisted he would not work with anyone in government who wanted to cut public spending too early.
As his party's crucial pre-election spring conference kicked off in Birmingham, Mr Clegg said it would set out plans for cutting Whitehall expenditure by £15 billion a year.
But he warned that "merrily slashing now" would be "an act of economic masochism".
The comments came amid intense speculation that the general election expected on May 6 could produce a hung parliament - with the Lib Dems potentially holding the balance of power.
The Tories have insisted that efforts to reduce the Government's spiralling deficit through cuts must start immediately, while Labour wants to delay action until the recovery is established.
Interviewed on BBC Radio 4's Today programme, Mr Clegg said his party backed significant reductions in spending.
"However, because of the frailty and the fragility of the British economy we do not think that should start in this financial year," he said.
"Self evidently I think, we think, that merrily slashing now is an act of economic masochism.
"So if anyone had to rely on our support, we were involved in government, of course we would say, no, do it sensibly.
"Do what myself and (Lib Dem Treasury spokesman) Vince Cable have been arguing for some time now which is explain to the British people and the financial markets that we have a better plan than anybody else to fill the black hole that Gordon Brown has created in the finances, but do it at a time when it is economically sustainable."
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