In an interview with The Daily Telegraph, the Deputy Prime Minister says graduates should face a new levy on their wages that will make the best paid contribute the most.
After adopting social mobility as one of his priorities in government, Mr Clegg says the tax is the best way to encourage more working-class children to go to university.
Nick Clegg fears expenses reform is being swept under carpet In endorsing the policy - first suggested by Vince Cable, the Business Secretary - the Liberal Democrat leader suggests it is of greater importance to him than securing electoral reform.
In the interview, Mr Clegg says he wants to send a "signal" that ministers want a new higher education funding system which puts the financial burden on people who have left university. "It's one we think is acceptable," he says.
Lord Browne, the former BP chief executive, is conducting an independent review of university funding.
But Mr Clegg makes it clear that if possible, the Government wants Lord Browne to draw up a plan for money to be taken from graduates after they complete their courses. "We're genuinely waiting for Lord Browne to try and work through the problems.
"But the signal I'm sending to you is that we will look very kindly at a system that ... is fair, progressive and encourages students from [poorer] backgrounds to apply," he says.
By contrast, increasing upfront fees would not be acceptable to Mr Clegg because it deters working-class children from going to university. "[Poorer] children are very intimidated by levels of debt. That is why I and my party have always been critical of tuition fees," he says.
"The perception of [a tuition fee] is that it imposes a wall of debt as you walk through the entry gates of university. This has a chilling effect on applications. It sends a signal which seems to be discouraging."
Mr Clegg concedes there would be difficulties, saying: "The question is whether you can make it work. You might not be able to."
University funding is one of the most divisive issues facing the Coalition. University leaders, backed by many Conservative MPs, want the cap on annual tuition fees to be lifted, allowing colleges to charge as much as £10,000 a year.
But the Lib Dems' election campaign promised to fight any increase in fees, which are unpopular with student groups. When Mr Cable floated the idea last month, it was thought that it was not being considered seriously at the highest level of government.
Mr Clegg's intervention suggests that the policy is, in fact, the Government's preferred option.
David Willetts, the Universities Minister, this week insisted that the Browne review should be allowed to report on the issue. Earlier this week, Mr Clegg said middle-class children had taken a "disproportionate" share of university places in recent years, and pledged to change the situation.
He promised that five years of the Coalition would deliver clear improvements in social mobility.
He pledged to break down the "social segregation" in which middle-class children dominated higher education and the professions.
In the interview, Mr Clegg says that work is more important to him than Lib Dem attempts to change the voting system, which was a central demand in entering a coalition with the Conservatives.
Ending the first-past-the post system is not "the be all and end all", and the Lib Dems will not walk out of the Coalition if their reforms are rejected, Mr Clegg says.
The Deputy Prime Minister talks down next year's referendum on electoral reform. If voters reject the proposed move to the alternative vote system it "won't be the end of the world", he says. "I'm not going to throw my teddies out of the pram."
A Downing Street spokesman said: "We are not going to pre-empt Lord Browne's review into university funding, the results of which we are expecting in due course."
Any move to impose a levy on graduates' pay would be controversial. Universities would not receive the funding directly. Instead they would have to rely on the Government to give it to them.
Critics of the plan claim it would remove competition between universities, with less popular institutions still guaranteed funding regardless of how many students apply.
Research suggested that under the scheme, professionals would end up paying tens of thousands more over their working lives for a university education than they did by paying annual tuition fees.
To avoid a public backlash, Mr Clegg signals that ministers are likely to present the post-university levy as a "graduate contribution" and argue that it is simply a deferred tuition fee.
"As soon as you mention a tax, people go a bit loopy," Mr Clegg says. "It's saying that students make a contribution, but we're not going to do it in a way that stops students applying, and we're going to make it dependent on how much benefit you get from going to university."
Withdrawing benefits from drug addicts and alcoholics who do not take up treatment would be "fundamentally inhumane", a senior Liberal Democrat has claimed.
The Government is considering financial sanctions for welfare claimants who fail to address their addictions, it emerged yesterday. Tom Brake, the chairman of the Lib Dem backbench committee on home affairs, said he and some colleagues would be opposed to the measure.