Taxes "must" be increased to cut the deficit after the next general election, Nick Clegg has said.
He also confirmed plans to collect a "mansion tax" on high value properties through new council tax bands.
The deputy PM told the BBC this would raise £1.5bn, which would be used to reduce the national debt.
The Lib Dem leader also accused Labour of "burying its head in the sand" over the deficit and the Tories of wanting to cut it by "beating up on the poor".
Mr Clegg told the BBC's Andrew Marr show it was not possible to "fill the black hole in the public finances either through spending reductions on their own... or by taxes on their own".
Only his party in government, he argued, could achieve the "stronger economy and fairer society" that the British public wanted.
Mr Clegg said his party's proposed "mansion tax" - a Lib Dem idea adopted by the Labour Party, which would involve a new levy on properties worth more than £2m - would be collected through new council tax bands, to cut down on red tape.
Unlike council tax, however, the money raised would go towards reducing the deficit.
Other tax changes proposed by the party - such as clawing back tax relief on the very largest pension pots - would be used to fund an extra £1bn a year for the NHS for two years.
'Tooth and nail'
Liberal Democrats at the conference have voted for a review of some of the coalition's key welfare changes.
Delegates called for a review of Universal Credit; reform of the Hardship Fund; changes to the Work Programme; an easing of benefit sanctions, and more support for claimants.
This will now become Lib Dem party policy - but it will not be be coalition policy and is not, ultimately, binding on the party leadership.
Mr Clegg has kicked off his party's final conference before the general election with a scathing attack on his Conservative coalition partners.
He said a freeze on working age benefits unveiled last week by the Conservatives showed David Cameron had "buried compassionate Conservatism".
At an eve-of-conference rally in Glasgow, Mr Clegg urged his party to fight "tooth and nail" to prevent a Conservative or Labour government.
Mr Clegg said: "Imagine again, if you can bear it, what it would be like in 2020, but this time with the Conservatives in government on their own.
"Britain, diminished and divided after a botched attempt to renegotiate our relationship with Europe and a vote to withdraw from the European Union."
He warned a Conservative leadership would be left "in hock to their right wing" with David Cameron "trapped between a poor man's Margaret Thatcher and a rich man's Nigel Farage".
And he claimed a Labour victory next May would mean a return to recession, soaring unemployment and a generation of young people "thrown back on the scrap heap".
He pledged to introduce a number of measures if the Lib Dems are in government again next year, including:
- Free school meals in primary schools
- Cut-price bus travel for young workers
- Extended paternity leave and free childcare
- "Proper" funding for the NHS
But he warned the party faithful they would have to "fight tooth and nail" ahead of next year's vote.
He acknowledged the party, which has seen poll ratings as low as 6%, faced "the fight our of lives" at the election.
Meanwhile, the chief secretary to the Treasury has said Lib Dems should be credited for the economic recovery - saying he was "disgruntled" the Tories had claimed the credit.
He told delegates: "We have to set the record straight. Just like I wrote this speech - we wrote the recovery plan. Just look at its main elements.
"Cutting taxes for working people - not a Conservative idea, a Liberal Democrat idea. A dramatic increase in apprenticeships - not a Conservative idea, a Liberal Democrat idea.
"Investment in infrastructure, including pushing for upgrades to the A1 and A303 - not a Conservative idea, a Liberal Democrat idea.
"Record investment in renewable energy - not a Conservative idea, a Liberal Democrat idea.
"Balancing the books, and doing so fairly. You ever hear that from the Tories? No! Absolutely core Lib Dem thinking. This recovery wouldn't be happening without Liberal Democrats in government."
Business Secretary Vince Cable attacked Conservative plans for a two-year freeze on working age benefits announced last week by Chancellor George Osborne.
He said it was "completely unnecessary that low income people will be punished, that the working poor should be punished, to give tax relief to people at the top end of the income scale".
The business secretary's comments come as a poll for BBC One's Sunday Politics suggested just 27% of Lib Dem candidates for next May's general election regard Mr Clegg as an electoral asset, while 45% disagree.
Just 36% said they were happy to use pictures of Mr Clegg on their campaign literature, according to the survey by ComRes.
The survey found 44% of Lib Dem candidates would prefer a coalition with Labour after the election, compared with 14% who would favour the Conservatives. Some 61% said the Tories had not been a good coalition partner.
Former party leader Paddy Ashdown, meanwhile, told activists the Conservatives were "reverting to type" and had become the "nasty party again".
Lord Ashdown added: "Labour will screw the economy and the Tories will screw the weak. Well, here's our message - we won't let them do it."