But he said that “over time” he hoped to secure a “fresh deal” for Britain in Europe, which would mean finding a way to obtain “the fresh consent of the British people”.
He made clear that he is leaving open the possibility that this could mean a referendum with the option of UK withdrawal on the ballot paper.
Pressed by Tory backbencher Julian Lewis, Mr Cameron appeared to concede he was willing to give his right-wing critics what they wanted amid fears Tory votes are seeping to UKIP.
Mr Lewis, the MP for New Forest East, asked: “Is it your position that, on any referendum on Europe, while you are PM, the option of voting to leave the EU will not appear on the ballot paper?”
Mr Cameron replied: “That is not what I’ve said.”
However, the Prime Minister said: “As Europe changes to meet the challenges of the eurozone, so our relationship with Europe will change, too.
“There are those who argue for an in-out referendum now. I don’t agree with that because I don’t believe leaving the EU would be best for Britain.
“Nor do I believe that voting to preserve the exact status quo would be right, either.”
He went on: “I don’t agree that the status quo is acceptable.
“But just as I believe it would be wrong to have an immediate in-out referendum, so it would also be wrong to rule out any referendum for the future.”
Labour leader Ed Miliband accused Mr Cameron of playing “hokey cokey” politics with the referendum.
Mr Miliband said the Prime Minister was leading a “party talking to itself” and the government was letting people down as a result.
He said: “It’s all about managing the divisions in his own party. But a ‘nudge nudge, wink wink’ European policy is neither good for the country nor will it keep his party quiet.”
But this was followed by a succession of Tory Eurosceptics demanding a referendum.
Leading Tory Eurosceptic Bill Cash said: “Will you take the advice of the London taxi driver who I’ve just spoken to, who said the British people are not stupid, they understand the position, give them renegotiation, give them a referendum, get rid of the coalition agreement, and then we will get re-elected by a massive majority?”
Tory MP Conor Burns, Margaret Thatcher’s former secretary, said: “The British public are heartily sick of broken promises on European referendums, not least because of the decision of the Labour party to renege on a referendum on the Lisbon Treaty.”
Edward Leigh, chairman of the Public Accounts Committee, said: “What the British people want is what they were offered in the only referendum they have ever been allowed to have – namely the common market, no more no less.”
Kettering MP Philip Hollobone said: “Given you are now not ruling out a future referendum on our membership of the European Union, isn’t it now time for the government to commission an official, full-scale, independent, comprehensive audit of the costs and benefits of our membership of the European Union, to better inform that referendum when it comes?”
There was a reminder from Conservative Philip Davies that the Lib Dems had an in-out referendum in their 2010 general election manifesto.
But Liberal Democrat deputy leader Simon Hughes said: “The coalition agreement is clear. There is a provision for a referendum if there is a handover of power from the UK to Brussels. There is no provision for any other referendum.”
The exchanges came after former defence secretary Liam Fox called for a referendum on creating “an economic not political relationship” with the EU.
Dr Fox said: “If this approach is rejected outright [by the EU] or falls short of necessary ‘red lines’, then we would have no alternative but to recommend rejection and consider departure from the EU.”
He insisted: “There is nothing to be scared of a future outside of the EU.”
Meanwhile, First Minister Alex Salmond accused Mr Cameron of contradicting himself in his calls for a referendum on Europe.
Mr Salmond said it was “extraordinary” that the Prime Minister should suggest holding an unspecified referendum on the UK’s European future while “threatening to obstruct” the independence referendum.
He said: “If Mr Cameron thinks it is the Westminster Parliament’s right to determine the parameters of an EU poll then equally clearly it is the Scottish Parliament’s to determine the parameters of a Scottish vote.”