David Cameron has said the Budget will show the "stark difference" between the parties on the deficit and recovery.
The Conservative leader said Labour's reluctance to start cutting spending this year was "completely wrong" and more urgency was needed on the issue.
And he attacked Labour for "appalling" claims the Tories would cut help for pensioners such as winter fuel rebates.
Labour said Mr Cameron did not have an answer to any of the key questions facing the economy and public finances.
The Budget comes weeks ahead of the start of the election campaign, with the poll widely expected to take place on 6 May.
At his monthly press conference, Mr Cameron criticised Mr Darling's recent comments that what the country needed would be a "workmanlike" Budget, saying much more "urgency, energy and vision" was needed to tackle the hole in the public finances.
He urged the government to reconsider its commitment to increase public spending this year and to delay cuts in government programmes to next year as "ludicrous".
Without prompt action to tackle the deficit, the UK faced slipping into a "danger zone" with rising interest rates and eroding confidence in the financial markets, he added.
Mr Cameron said the Conservatives would publish the Budget in full on the party's website to allow the public to comment on the details - an online technique known as "crowd sourcing".
He said Labour had "form" on talking up election giveaways but burying the "nasty stuff" in the small print of the document.
Mr Cameron declined to comment on reports that an incoming Conservative government would have to find £31bn of spending cuts.
The Tories have said they will spell out more details of proposed cuts after the Budget but Mr Cameron said his party had already set out "the difficult choices" that would be needed.
Mr Cameron said suggestions that the Tories would cut the winter fuel allowance and other help for pensioners were Labour "lies".
He said his message to pensioners worried about his plans was "very clear": "I know you are getting letters from Labour saying the Conservatives would cut the winter fuel allowance, the free bus travel, the free TV allowance.
"Those statements by Labour are quite simply lies. A Conservative government would keep... these things. Do not be frightened by a government that is trying to scare you into not opting for change."
Saying he felt "very strongly" about the issue, he called on Gordon Brown to intervene to stop Labour candidates from telling "lies" about Conservative policy.
"They are appalling people," he added. "The sooner they are out of the government of this country the better."
Labour said that, unlike the Tories, it had a credible plan to cut the deficit in half over four years and to use public spending to stimulate private sector investment in the economy and drive growth.
"When it comes to the economy, he couldn't answer even the most basic questions," Treasury Chief Secretary Liam Byrne said of Mr Cameron's pre-Budget comments.
"How much is he planning to cut from spending in 2010-11? He wouldn't say. How quickly would he halve the deficit? He wouldn't say.
"By how much would he reduce the structural deficit? He wouldn't say. Unlike Labour, he can't answer a single one of these questions."
The Lib Dems have said cross-party agreement is needed over how to bring down the deficit but agree spending should not be cut until the recovery is more sustained.