Detailed arguments over spending and tax will continue
Labour unveiled a dossier claiming the Tory figures were an "incoherent mess".
But the Tories retaliated with their own document saying they had already refuted all the claims. They accused Tony Blair of "losing the plot".
The Lib Dems, whose leader Charles Kennedy is celebrating becoming a father, focused on their own tax plans.
How do they [the Conservatives] square this economic circle?
Tony Blair
Analysis: Tory manifesto Fact check: Tory budgets
The Tories say they can lower taxes, reduce borrowing and raise public spending in key areas by cutting waste. They brand Labour's attacks as "desperate smears".
Shadow Treasury spokesman George Osborne said that tax cuts would be set in motion in the first Budget, if the Tories won the election, but not come into effect until the next financial year.
That prompted Gordon Brown to say Tory tax plans were "unravelling".
Mr Brown said: "When all plans are taken into account, Mr Letwin has a black hole of £18.9bn in year one, £18.5bn in year two and £14.4bn in year three."
The cash gap would require either "huge" spending cuts or increased borrowing - which the Bank of England would have to take into account and put pressure on interest rates.
Shadow chancellor Mr Letwin hit back, telling BBC News: "On our spending plans it will be possible for us both to reduce borrowing and avoid the tax rises that are implied by Labour's spending plans after the election and to cut taxes by £4bn."
Party savings claims Labour Party plans £21bn efficiency savings 100,000 civil service jobs will be axed or changed Lib Dems say they can reduce spending by £26bn by axing the DTI and other savings Tories plan £35bn in savings 235,000 jobs to go, 91,000 into the private sector 40,000 reduction in recruitment freeze 20,000 voluntary redundancy
Kennedy joy at son's birth
Mr Letwin said that Labour would have to raise taxes if they were re-elected to cover their commitments.
"This election is not about questions of accountancy, whether you can or you can't achieve a particular change in a particular department on a particular timescale.
"This election is about a massive question of choice for the British public."
The Conservatives also suggested Labour was trying to "cover up" a likely rise in council tax bills in England as a result of property revaluations, which in Wales had led to an average increase of 9%.
Labour called the claim "scaremongering" and said Wales was not a precedent for council tax in England.
New taxes
Lib Dem frontbencher David Laws branded the Conservative plans "unrealistic".
He said the Tories were offering only £13.3bn of genuinely new savings - and £5.5bn of those were unachievable.
HAVE YOUR SAY What's obvious is the amount of tax we're all paying now - the party that can do something about that will get my vote
Barbara, Kent
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Treasury spokesman Vince Cable meanwhile highlighted Lib Dem plans for the economy.
He said the 50p tax rate on earnings over £100,000 would fund the scrapping of university tuition fees and the introduction of free personal care for elderly and disabled people.
The new tax rate would also help plans to replace council tax with a local income tax. The party says the move would be fairer even though some people would have to pay more.
Among the smaller parties, the Greens unveiled their manifesto, claiming to be the only party committed to a more just society with "the planet at its heart".
The Conservative Party manifesto, launched earlier today, has been criticised by opponents as being unrealistic.

The pledge of £35 billion of savings from "government slimlining", and subsequent tax cuts, has been attacked by Labour and the Liberal Democrats.  The Conservatives plan to continue funding front-line services at the current rate by relying on economic growth to make up the difference.  

Labour described the plans as "a complete economic mess", the current Chancellor, Gordon Brown claiming there would be a shortfall of "£18.9bn in year one, £18.5bn in year two and £14.4bn in year three."  Labour leader Tony Blair claimed that the Labour and the Conservatives economic roles had reversed since the 1980s, when many had lost faith in Labour's ability to handle the economy.

The deputy leader of the Liberal Democrats, Sir Menzies Campbell, claimed that £5.5 to 8 billion of cuts were unrealistic.

Labour's manifesto is launched tomorrow, and the Liberal Democrats launch theirs on Thursday.  Conservative shadow Chancellor Oliver Letwin has already criticised Gordon Brown's budget of March this year, claiming it will create an £11bn shortfall.