The party plans to invest in wind energy, energy efficiency in public buildings and homes, and in bringing empty homes back into use through renovation.
Speaking at a press conference in Cardiff, Mr Clegg said that, for decades, a succession of Labour and Conservative governments had run Britain to "serve the interests of one square mile - the City of London".
He said: "We want to build a new economy which serves the interests of the 100,000 square miles of the UK, where we have growth that lasts."
The Liberal Democrats plan to create a one-year green job stimulus plan, for which £3.1 billion of cuts in government expenditure would be used to bring 200,000 empty properties back into use, and invest in new green energy infrastructure and public transport.
There would also be a "90-day guarantee" for young people, who would be offered a place of training, work or apprenticeship after 90 days of unemployment, so they were not "left in a state of despair".
Mr Clegg said: "We need all this infrastructure in any event but, of course, investing in that infrastructure is the best way to create jobs, particularly for young people today."
He also declared that the General Election campaign was "starting to come to life" as a clutch of opinion polls showed an upsurge in support for the Liberal Democrats.
"I think this General Election campaign is starting to come to life for the simple reason that a growing number of people are starting - it is only a start - starting to believe, starting to hope, that we can do something different this time," he said.
"That the old tired choices that they have been given by the old parties of the past, no longer need to govern the way in which we run politics in the future.
Mr Clegg said: "The opportunity is before us to use the crisis of climate change, and climate science tells us that this is our last chance for change, to use that crisis to help mould and shape a fundamentally new approach to growth in the British economy."
He added: "Over the longer term, we will fund the transition to a green economy through a UK Infrastructure Bank - an idea first set out by Vince Cable and now adopted by the other parties."
Energy and climate change spokesman Simon Hughes then outlined the series of plans to create 30,000 jobs by investing in wind energy, energy efficiency in public buildings and homes, and bring empty homes back into use through renovation.
There would be extra support for young people with 800,000 internships to help build up their experience.
He said up to a million people could take part in an "eco-cashback" scheme to give people £400 towards energy-efficient home improvements and small energy generation projects.
People will be able to apply for the cash to help pay for double-glazing, boiler upgrades and micro-generation such as solar panels, and domestic wind turbines, he said.
Mr Hughes said: "We don't want this just to be a scheme that deals with the public institutions or the corporate sector, we want real people to start feeling they can make a contribution and that would be a £335 million package, creating 8,000 jobs."
He said he wanted to make "as many schools as possible" much more energy-efficient. Schools could be lent money to make improvements, which they could then pay back through savings on their bills.
Mr Hughes claimed that 250,000 empty homes could be brought back into use. People who own these homes would get a grant or a cheap loan to renovate them so they could be used.
The party would also set up a bus scrappage scheme at a cost of £140 million to help bus firms replace old polluting vehicles with new low-carbon ones.
It was put to him that the better the Liberal Democrats did, the more the chance that Prime Minister Gordon Brown would be back in Downing Street after the General Election.
Mr Clegg said: "I hear these constant allegations and counter- allegations from the Conservatives. It is not fact at all, of course it is not.
"I have leaflets in my city of Sheffield with Labour saying a vote for the Liberal Democrats will give support to the Conservatives, and I have got the Conservatives saying precisely the reverse.
"Of course both of the old parties are going to lash out and claim that a vote for the Liberal Democrats is somehow a vote for another party."
He added: "We know - again, fact - that an increasing number of people over the last few days... we don't know what is going to happen in the future, but seem to be open to the idea, in growing numbers, of doing something very different.
"To short-circuit that process and then repeat this tired old claim that a vote for the Liberal Democrats is a vote for another party, misses, in my view, the blindingly obvious which says that a vote for the Liberal Democrats is exactly what is says on the tin - it is a vote for the Liberal Democrats.
"It is a vote for our policy on fairer taxes, on schools, on a new approach to the economy on cleaning up politics, nothing more, nothing less."
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