Nick Clegg has set out proposals to curb benefits to European Union migrants without "tearing up" freedom of movement rules within the 28-member bloc.
David Cameron is due to set out his own plans to restrict EU migration in a highly anticipated speech in the coming weeks, but Mr Clegg warned the Tories were in danger of making "irresponsible declarations" on Europe in a bid to quell unrest at the rise of Ukip.
Instead the Liberal Democrat leader insisted the UK could find allies in Europe to support efforts to tackle so-called "benefits tourism" without challenging the key principle of free movement which is regarded as non-negotiable by countries including Germany.
Mr Clegg suggested that migrants could be prevented from claiming the new universal credit until they have "worked and contributed" to the system.
He also proposed restricting access to in-work benefits like tax credits, suggesting that migrants could be required to work the equivalent of full-time hours on the minimum wage in order to qualify.
Mr Clegg warned the Prime Minister's speech could put the British economy at risk if he proposes measures which would jeopardise the country's EU membership in an effort to win back supporters from Nigel Farage's Ukip.
Writing in the Financial Times, Mr Clegg said Mr Farage wanted to "pull up the drawbridge" and acknowledged it was a "message that has played well" in the by-elections in Clacton and Rochester and Strood.
But he said: "The bigger danger now is that a rattled Conservative party resorts to equally irresponsible declarations, in a bid to calm their own ranks.
"David Cameron will soon give his much built-up immigration speech. If the Prime Minister asserts that a Tory government will introduce caps or overall quotas on the number of EU migrants coming here, we will find ourselves in the worst of all worlds.
"Ukip will say it is not enough. Europe will say it is not possible. Once again the British people will be plunged into a cycle of wild overpromising and inevitable disappointment, their scepticism confirmed. And the risks to the openness of the British economy will be considerable."
Mr Clegg said it would be possible to work with allies in Europe to secure reform within the existing freedom of movement rules.
The Deputy Prime Minister, who was expected to discuss the issue German vice-chancellor Sigmar Gabriel during a visit to Berlin, said: "I have already proposed that we work with other states to stop EU migrants from claiming child benefit for children who are not living here.
"As a first step, we should pay the same rate as the country in which those children reside. In the UK it is about £80 a month, whereas in Poland it is less than half that. And there are other proposals we must now explore.
"As we streamline our welfare system by combining a range of benefits in a single Universal Credit, we should make sure that only migrants who have worked and contributed can receive the support.
"New jobseekers should not be eligible. Applying the same principle - that support should be reserved for migrants who are paying something into the pot - we should look at increasing the earnings threshold for in-work benefits such as tax credits. EU migrants could, for example, be required to work the equivalent of full-time hours on the minimum wage in order to qualify."
He said Germany was pursuing five year re-entry bans for migrants involved in identity or benefit fraud, suggesting that "we must see if we can strengthen our laws as well".
Crucially, he said these measures could be pursued "without tearing up the freedom to move across Europe or threatening to pull out of the EU".
"The choice is clear," he said. "We can feed people ever more irresponsible claims about immigration, raising hopes only to dash them in the end. Or - far better - we can reform the rules to address people's legitimate concerns, while safeguarding our open economy too."Suggest a correction