Following speculation that he may block a repeat of the TV clashes which dominated the 2010 election, the Conservative leader insisted: "I want the debates to take place."
But he said that the format could be tweaked to ensure that the rest of the campaign is not overshadowed.
Mr Cameron told BBC1's Andrew Marr Show: "I want the debates to take place. They were good in the last election."
But he added: "I thought they took up too much of the campaign, so I think we could start them a bit earlier.
"My only regret is that if you are leading a political party, the election campaign is a moment when you really want to get around the country, you want to have arguments and interviews, and I found the whole election was just the run-up to the debate, the debate, and the analysis of the debate.
"Now we've got a fixed-term Parliament, we can stretch those things out a bit."
Mr Cameron said there was "lots of time for negotiation" over the exact format of the broadcasts before the election scheduled for May 2015.
But he made clear that he does not believe that the UK Independence Party leader Nigel Farage should be invited to take part alongside himself, Liberal Democrat leader Nick Clegg and Labour leader Ed Miliband.
"I think the debate predominantly should be about people who have a prospect of becoming Prime Minister," said Mr Cameron.
Asked if he thought that Mr Farage was among the figures who could potentially become PM, he replied: "I don't think so, no."
Mr Cameron once against dismissed suggestions that he should take part in a televised debate with Scottish National Party (SNP) leader Alex Salmond ahead of the 2014 Scottish independence referendum.
"Alex Salmond wants the question to be about anything other than the question," said Mr Cameron.
"So he would like the debate to be the SNP versus the Tory Party or Scotland versus England. It's not - it's a debate between Scots.
"What it should be is between Alistair Darling, leader of the No campaign, and Alex Salmond, leader of the Yes campaign.
"Let them debate. But he wants to change the question. He's a canny guy but I saw that one coming."