Mr Darling has pledged to halve the deficit in four years
The chancellor has warned that Britain faces the toughest spending cuts in 20 years if Labour is re-elected.
Alistair Darling said prime minister Gordon Brown "accepts and knows" that reducing government borrowing was "never negotiable".
"Once recovery is established, we have to act," he told the Times newspaper.
But shadow chancellor George Osborne said there was still "complete confusion" within government about cutting public spending.
He said only the Tories could fix Britain's debt crisis.
In the interview, Mr Darling said: "The next spending review will be the toughest we have had for 20 years... to me, cutting the borrowing was never negotiable. Gordon accepts that, he knows that."
He also said Labour had to regain the middle ground to win the election and confirmed there would be a pre-election budget.
'Cut to the bone'
Mr Darling said electors support his plan to balance the books.
"Most people know that public spending has doubled over the last 10 to 12 years, so we are coming off a much higher base, " he said.
"We are not talking about a situation where we have already cut to the bone."
The Times says Mr Darling declined to to say whether he put any conditions on his continuing support for the prime minister, following last Wednesday's call for a leadership ballot by two former cabinet ministers.
Mr Darling eventually backed the prime minister, but only after a delay lasting several hours, and following a face-to-face meeting with Mr Brown.
Mr Osborne said there was still conflict between Mr Darling's plans and those of the prime minister.
"We've got complete confusion in the government," he said. "We've got Alistair Darling saying spending has got to be cut and Gordon Brown saying it's going to go up.
"We need a strong, united, Conservative government to get this country back on its feet."
Mr Osborne, who has just returned from a visit to Afghanistan, also said that despite planned cuts, "our spending on our troops in the front line is protected."
Vince Cable, Liberal Democrat Treasury spokesman, also said there was "an alarming divide" between Mr Darling and Mr Brown.
"We desperately need a more coherent approach to this problem," he said. "The economy can't be managed on the back of power-play between government ministers."
BBC political correspondent Iain Watson said confirmation of the pre-election budget was designed to stem speculation there may be an early election.
By law, there has to be three months between December's pre-budget report and the actual budget, making a March election all but impossible.
Labour has been criticised by its opponents for not spelling out how it would deliver the pledge to halve Britain's deficit over a four-year period.
Our correspondent said to retain the confidence of the markets the chancellor wanted to talk tough about what would happen if a Labour government is re-elected.
He also indicated that it was essential for Labour to regain credibility with middle-class voters and stressed that election could only be won if his party recaptures the middle ground.