Nick Clegg will make a direct appeal to disaffected Labour supporters thinking of voting Tory at the next election, in his speech to the Lib Dem conference.
Nick Clegg will shun talk of deals with other parties in a keynote conference speech and instead tell Lib Dems: "I want to be prime minister."
"You don't think we're contenders. I urge you to think again," he will say.
The Lib Dem leader is bidding to reassert his authority after a bruising week - and reach out to disaffected Labour voters thinking of voting Tory.
The Lib Dem leader will urge them not to sleepwalk into a Tory government because they think it's the only option and to vote for "real change" instead.
He will urge them not to sleepwalk into a Conservative government and opt for "real change" instead.
Mr Clegg is facing a revolt from within his party over his repeated insistence on the need for public spending cuts.
The Lib Dems say their private polling shows the next election is "wide open".
Senior MPs have criticised moves to means-test child tax credits and have accused him of preaching "doom and gloom" with his call for "savage" cuts.
Instead of talking about what might happen in the event of a hung Parliament, Mr Clegg will focus on what a Liberal Democrat government would do.
He will stress the party's commitment to fairer taxation and vow to "clean up" Westminster politics including MPs' expenses. He he will propose a 90 day job guarantee for unemployed young people paid for by scrapping Labour's VAT cut.
Mr Clegg will attempt to reassert his authority - and breathe some fire into the belly of rank-and-file members in Bournemouth - in what will be his final annual conference speech before the next election.
'Mansion tax'
Aides say it will be "serious" speech setting out the scale of Mr Clegg's ambitions for the party and the country and he will deliberately avoid talk of coalitions with other parties.
He will also harden his line on Afghanistan - saying there was "one more chance to turn things around".
The party's private polling shows the next election is "wide open" and that the Lib Dems stand a chance of forming a government, they told reporters.
Mr Clegg will deliver a message to voters who do not usually vote Lib Dem or have given up on voting altogether, telling them: "Don't stay at home, don't vote Conservative just because you think it's the only option."
"I know some of you believe we should call for British troops to withdraw now," he will tell delegates in Bournemouth.
He will say: "If you supported Labour in 1997 because you wanted fairness, you wanted young people to flourish, you wanted political reform, you wanted the environment protected, or you simply believed in a better future, turn to the Liberal Democrats.
"If things continue on the present disastrous course, then sooner or later that is a judgement which we may need to make."
"I know there are people who agree with a lot of what we've got to say, but who still don't vote Liberal Democrat. You don't think we're contenders. I urge you to think again."
But there will be no mention of dropping a pledge to scrap university tuition fees from its next manifesto - a suggestion which sparked open warfare in the party at the start of the week.
'People want hope'
He will briefly mention Vince Cable's £1m "mansion tax" in a section on rebalancing the tax system so that the wealthy pay more.
Mr Clegg will argue that voters have a choice at the next election between the "fake change" of the Tories and "real change" from the Lib Dems.
'Progressive austerity'
Mr Clegg has faced a battle this week with his own MPs and party members, after saying "savage" spending cuts were needed to tackle Britain's record debts.
The 0.5% levy on owners of £1m-plus homes sparked a backlash from some of the party's senior MPs earlier in the week, prompting an admission from the Treasury spokesman that he could have consulted more widely before announcing it.
He also ruffled feathers by suggesting a "debate" on whether child benefit might have to be cut for better-off families, although he stressed in a BBC interview that the principle of universal benefits was "important".
Mr Clegg will also address criticism from former leader Charles Kennedy, who said the party was in danger of losing its "heart" with Mr Clegg's talk of "savage" spending cuts.
Work and pensions spokesman Steve Webb told delegates: "I think we have over-done the despair."
Miriam Clegg, leader's wife, has just taken her seat #ldconf16 minutes ago Party starting awards ceremony-hardly the BAFTAS, but thankyous to party activists who do the hard graft27 minutes ago Conference hall already nearly full-gurkhas have their hats on and are in front row-Clegg on stage five past three34 minutes ago Baroness Scotland's former PPS tells Radio 4 she should go as a matter of 'personal honour' About 1 hour ago Lib dems claim their polling suggests the next election is 'wide open' but won't yet show us the research About 2 hours agoWhat is this?
Miriam Clegg, leader's wife, has just taken her seat #ldconf 24 minutes ago Party starting awards ceremony-hardly the BAFTAS, but thankyous to party activists who do the hard graft 35 minutes ago Conference hall already nearly full-gurkhas have their hats on and are in front row-Clegg on stage five past three 42 minutes ago Baroness Scotland's former PPS tells Radio 4 she should go as a matter of 'personal honour' About 1 hour ago Lib dems claim their polling suggests the next election is 'wide open' but won't yet show us the research About 2 hours agoWhat is this?
He added: "Doom and gloom does not inspire and motivate people. People want it straight but they also want hope."
Unlike Labour and the Tories, the Lib Dems had "come clean" about what cuts were needed and were guided by principles of fairness, he will say.
Mr Clegg hit back by saying: "I know people want me to use softer language. It won't make the problem go away."
"Not just austerity, but progressive austerity. Reducing the deficit, yes, but also building a fair society and a green economy.
The Lib Dem leader won his battle to include a proviso in the party's draft manifesto that some pledges might have to be dropped once full costings have been produced.
"Still driven by generosity of spirit, but fit for the circumstances of the day. It's the only way to deliver real change in Britain."
But the party's Federal Policy Committee, which decides what goes in the final version of the manifesto, has said a "clear majority" of its members did not want to scrap the party's commitment to end tuition fees for undergraduates in England - something Mr Clegg has suggested might be needed.
He will speak at length about what Britain would be like if the Lib Dems were in power, in what aides were saying is the most ambitious speech ever given by a leader of their party.
In a letter to Mr Clegg the committee said: "Our party makes policy in an open and democratic way and... policies cannot be changed merely by assertion to the contrary."
"I want to be prime minister because I have spent half my lifetime imagining a better society. And I want to spend the next half making it happen," he will tell the party faithful.
But former party leader Sir Menzies Campbell said Britain's economic situation had complicated the issue of tuition fees.
Mr Clegg will end by delivering a message to voters who do not usually vote Lib Dem or have given up on voting altogether, telling them: "Don't stay at home, don't vote Conservative just because you think it's the only option."
"If you find that you have to choose between making a concession which doesn't presently exist or cutting frontline education and health services then that's a very hard choice," he told the BBC.
He will say: "If you supported Labour in 1997 because you wanted fairness, you wanted young people to flourish, you wanted political reform, you wanted the environment protected, or you simply believed in a better future, turn to the Liberal Democrats.
"That's the kind of argument that we are going to have to have in the country in due course.
"I know there are people who agree with a lot of what we've got to say, but who still don't vote Liberal Democrat. You don't think we're contenders. I urge you to think again."
"We're having it here in an honest and open fashion."
Treasury spokesman Vince Cable, who will front the party's general election campaign with Mr Clegg, has also faced a backlash from some of the party's senior MPs over his alleged failure to consult them on his "mansion tax" proposals.
Mr Cable was told by one that the policy of taxing the owners of £1m plus homes was "complete codswallop," while another told the BBC it had left the Lib Dem Treasury spokesman "seriously damaged".
Sir Menzies added: "It wouldn't be a Liberal Democrat conference if there weren't one or two people who were concerned about the direction."
