Clegg defends budget ring-fencing amid reported unease among ministers
Nick Clegg has said he is "adamant" the NHS, schools and overseas aid should still be protected from cuts, amid reports colleagues are unhappy about the effect on their departments.
The deputy prime minister said ring-fencing budgets was the right decision.
Four ministers are asking for some of their department's spending to be reclassified to fall within protected areas, the Financial Times says.
The government's review of spending for 2015-16 will be announced in June.
The coalition has said it must find substantial further savings for the period in question, which extends beyond the lifetime of the current Parliament and the expected date of the next election in May 2015.
Tuesday was the deadline for ministers to set out what level of cuts they believe are achievable then.
Reports have suggested areas of expenditure without protection face cuts of between 5% and 8%, on top of the squeeze in spending already announced since 2010.
The health service, schools in England and overseas aid have all seen a real-terms increase in funding since 2010, while other departments have seen their budgets cut by an average of 19%, as savings of more than £80bn are sought.
According to the Financial Times (FT) newspaper, Defence Secretary Philip Hammond, Business Secretary Vince Cable, Justice Secretary Chris Grayling and Local Government Secretary Eric Pickles have called for work done by their departments in areas such as military healthcare and medical research to be re-classified as health spending in future - which would lead to cuts in overall NHS expenditure.
Mr Hammond has said further cuts will leave the military in a "extremely taut" state, while Mr Cable has suggested the policy of ring-fencing certain departments is "very unbalanced".
But the deputy prime minister told BBC Radio 4's World at One programme: "I am absolutely convinced that at a difficult time like this, protecting NHS spending, protecting spending on schools, honouring our international obligations to developing countries around the world, was a big decision, was a controversial decision but I think was the right one to take and the right one to stick to."
He added: "I think we are right, and I am adamant about this, to stick to retaining those protections.
"The consequences are that there are knock-on effects on those departments that are not so-called 'protected'."
The FT says the Treasury has asked other departments to see whether any of their spending can be reclassified as international aid, whose activities are strictly defined, to help ease pressures.
Asked about the reported grumblings of ministers in unprotected departments - dubbed the National Union of Ministers by the media - he accepted they were "marshalling their forces" to argue for their priorities.
But he said this was "part of the argy-bargy" common to all spending rounds.
Although the Ministry of Defence has not commented on the spending round, Mr Hammond told the BBC earlier he "absolutely guaranteed" injured servicemen would continue to receive the treatment they needed.
'Dividing the cake'
The deputy prime minister rejected suggestions a decision on the scale of cuts had been taken, saying negotiations were "being played out in Whitehall at the moment" and had yet to be resolved.
"Until we know how the cake is divided between different departments, I cannot give you percentage figures," he said.
"I simply don't know what the answer is.
"No-one does know how it will settle down before we make these decisions in June."
Mr Clegg said he would not support further cuts in benefits, on top of the £3.5bn announced in last year's Autumn Statement, unless there was agreement the better-off should take the biggest share.
Prime Minister David Cameron has rejected calls for wealthier pensioners to be asked to forgo some universal benefits - such as winter fuel allowance and free bus passes - in the current Parliament.