The government will not change course on spending cuts, Deputy Prime Minister Nick Clegg will tell the Liberal Democrat conference later.
The Treasury has denied BBC reports ministers are considering a £5bn rise in spending on infrastructure in a bid to kick-start the UK's stalled economy.
Mr Clegg will stress in his speech that boosting growth is a top priority.
And despite the public spending squeeze the government is not "helpless" to halt rising unemployment, he will say.
The comments come after the International Monetary Fund cut its growth forecast for the British economy and said the government should delay its deficit reduction programme if growth slowed further.
The coalition has already brought forward spending on some infrastructure projects but BBC political editor Nick Robinson said cabinet ministers were in the early stages of discussions about injecting £5bn extra into the economy to boost growth.
Such a move would represent a U-turn by the coalition and was immediately denied by the Treasury and Lib Dem cabinet ministers Danny Alexander and Chris Huhne, who both said they "did not recognise" that figure.
"The government has set out its spending plans and is sticking to them," said a Treasury spokesman.
Mr Clegg will focus strongly on the economy in his speech - but he will not announce any new measures to boost growth.
He will use the speech to reassure party members that they remain a distinct political force and that manifesto commitments on reducing the tax burden of the lowest-paid, providing more money for the most disadvantaged pupils and restoring the link between earnings and pensions, have been delivered.
Responding to last month's riots in England, Mr Clegg will say the disorder showed that some young people "had fallen through the cracks" and had "nothing to lose" by their actions.
"It was about what they could get here and now, not what lies in front of them tomorrow and in the years ahead," he will say.
Some of those involved "lost touch with their own future" years before the riots, he will argue.
The Lib Dem leader will also announce a programme of catch-up summer classes for children "most in need" prior to starting secondary school.
"So often the people who have gone off the rails are the ones who were struggling years earlier," he will say. "This is a £50m investment to keep them all on the right path."
The Lib Dems have been trying to regroup after suffering heavy losses in council elections in England and Scotland.
The party also suffered a defeat in a referendum on the UK voting system, when the alternative vote campaign it backed was overwhelmingly rejected by the voters.
Despite these reverses and continuing poor poll ratings, Mr Clegg has insisted he will remain in his job "well beyond" the end of the current parliament.
The conference speech - which brings the five-day event to an end - is Mr Clegg's second as deputy prime minister and his fourth since becoming Lib Dem leader.