An extra £5bn of capital investment, funded by spending cuts elsewhere, will form the centrepiece of an overall £30bn national infrastructure programme due to be announced by George Osborne on Tuesday as part of an attempt to prevent the country from sliding back into recession.

The chancellor will unveil nearly 500 public sector projects, many of them to be funded by commercial pension fund investments.

Danny Alexander, the chief secretary to the Treasury, said the public money made available was being re-allocated from the spending review to a "more productive purpose" to ensure "the very best use" is made of the limited resources.

He told BBC Radio 4's Today programme thar areas of departmental "underspends" were being identified along with areas where project deadlines have slipped.

"We are very much sticking to the plan that we've set out," he said. "If anything, the case for that is reinforced by the problems we are seeing in the eurozone and elsewhere."

Some of the £5bn extra capital investment over the next three years will go to a £600m schools programme to fund an extra 40,000 places by 2014. In what is rapidly turning into a full scale "game-changer" budget to stave off the impact of collapsing European economies, Osborne will also announce plans to:

• Help energy-intensive industries.

• Increase the bank levy to maintain an annual income from banks of £2.5bn.

• Place a cap on announced rail fare rises.

• Defer a 3p rise in fuel duty which was due to be introduced in January

• Remove health and safety bureaucracy from 1 million self-employed people as the next stage of labour market deregulation.

He is also expected to announce a deal designed to unlock £40bn of bank lending for small businesses in which the government will underwrite the lending.

Alexander told Today: "Investment in infrastructure is one of the most productive ways that you can use both public money and indeed private money too to deliver both of those objectives, and so we'll be allocating some government money in this spending review, we'll be signalling some longer-term projects that we're going to fund in the future, and crucially through working with British pension funds, we are identifying ways to unlock around £20bn of pension fund investment to go into privately-funded infrastructure in this country."

On the public funding being made available, Alexander said: "Part of my job as chief secretary is to look at departmental budgets around government to identify areas where there are underspends or where projects haven't come to fruition on the right time scale.

"For example, the carbon capture and storage programme has been delayed because the original project couldn't be delivered and so we are committed to providing the money for that but it is more likely the majority of that money will be needed in the next parliament and so we can release the funds in this parliament for this sort of programme.

"So there are a few decisions we have made - obviously the chancellor will set those out tomorrow. Some of those are difficult decisions."

The Treasury is disgorging its growth strategy before the autumn statement since it knows the day itself will be dominated by the Office for Budget Responsibility's new forecasts for growth, borrowing, unemployment and their consequences for its goal of eradicating the structural deficit by 2015-16.

Speaking on the BBC's Andrew Marr Show on Sunday, Osborne admitted the OBR forecasts would be downgraded, saying: "This is an exceptionally difficult time. We have a slowing economy, a slowing world economy, we have this financial crisis brewing in Europe."

But he insisted he would stick to his deficit reduction target, saying: "I am absolutely clear the government will do what it takes to meet its fiscal mandate, to meet its debt target." He has until 2015-16 to meet this target.

With the autumn statement due to be fiscally neutral, Osborne has had to find nearly £8bn in savings to fund the additional £5bn capital investment, as well as the delay in the fuel duty rise and the higher than expected costs of benefit upratings. Some of that will come from lower than projected spending across Whitehall and higher corporate tax receipts, but he is also planning to freeze some working tax credits at the higher income end.

The chancellor may also be able to garner funds for the investment from overseas. China Investment Corporation is considering investing in the infrastructure of the UK, according to Lou Jiwei, the fund's chairman. The $410bn Chinese fund "is keen to team up with fund managers or participate through a public-private partnership in the UK infrastructure sector as an equity investor," Lou writes in today's Financial Times.

In an attempt to start winning the political argument on the economy, Labour plans to seize on Tuesday's higher projected public sector borrowing figures to claim the government will be borrowing to fund recession through higher welfare bills, while Labour would borrow to fund growth and ultimately higher tax receipts.

Government sources said ministers want to focus resources on protecting the "squeezed middle" and on finding job-creating capital investment in schools, roads, railways, high-speed broadband and energy projects.

The National Infrastructure Plan will draw on £5bn extra capital spending in the current spending period to 2014-15, £5bn extra spending in the following spending period and up to £20bn from a deal with pension funds. It will need guaranteed income streams for the risk-averse pension funds, such as tolls for new roads, or guaranteed income from power stations.

The government has signed a memorandum of understanding with the National Association of Pension Funds (NAPF) and the Pension Protection Fund (PPF) to develop a new pension infrastructure platform, and make it easier for pension funds to invest in projects such as renewable energy, power stations and ports.

The scheme is in some ways a substitute for Labour's private finance initiative that the government has declared has provided poor value for taxpayers money.

The National Infrastructure Plan will set out 40 top priority schemes among a longer list of 500 projects.

Joanne Segars, chief executive of the NAPF, said: "We're excited by the government's commitment to try to make it easier for pension funds to back major infrastructural projects.

"This could be a real win-win. The UK desperately needs to update its infrastructure, and pension funds are looking for inflation-linked, long-term investments.

"Pension funds hold over a trillion pounds in assets, but only around 2% of that is invested in infrastructure. There's the potential for that to be much higher".

Pension fund investment in infrastructure has been pioneered in Canada, Australia and was embraced by the former business secretary Lord Mandelson in 2010.

Osborne hopes to conclude negotiations within the next three or four months.

Ministers have also responded to lobbying from energy-intensive industries about the cost of the government's climate change levy and the European emissions trading scheme. Osborne will announce a £250m package of support, which will include increasing relief from the climate change levy from 65% to 90% in April 2013 for industries that sign agreements with Whitehall to cut their use of carbon.

Osborne refused to be drawn on the latest economic and financial forecasts from the Office for Budget Responsibility, the independent body set up by the chancellor in the aftermath of the last election.

However, the OBR is expected to say that the UK will grow by around 1% both this year and in 2012, down from 1.7% and 2.5% in March. Lower growth will result in higher borrowing, but Osborne insisted that sticking to the plans for budget austerity was vital in ensuring that market interest rates in the UK stayed low.

Osborne said that credit easing would involve the government underwriting commercial banks so that they could borrow more cheaply in the financial markets, with the benefits passed on to companies in the form of lower interest rates.

"The government will underwrite the loans the banks make to small businesses in order to cut the interest rates the small businesses pay," Osborne said.

"We are making available £20bn for the national loan guarantee scheme; however, it sits within an envelope that could be as large as £40bn.

"These are guarantees. We are not borrowing this money; we are underwriting the loans that are being made."

It is understood that the second £20bn of loan guarantees is being held in reserve for the moment but could be made available in the next two years.

A third scheme would offer an alternative to traditional bank loans by encouraging firms to sell bonds – or company IOUs – to the market.