They would follow the same format, with the broadcasters drawing lots to decide which channel screens the first debate.
Tony Hall, director of BBC News, urged the parties to take part.
He said: "Televised leaders debates are a familiar part of the electoral landscape across the democratic world and it's time British voters had the same opportunity to see the politicians in action."
'Important'
Steve Anderson, ITV controller of news and current affairs, said: "We are setting aside the usual trench warfare between news broadcasters and uniting behind this important project."
Similar debates in the US in recent years have attracted huge audiences.
Other broadcasters would have free access to the debates, including Sky News, BBC News 24 and the ITN News Channel.
Parties in Scotland and Wales have also been invited to take part in separate debates on the BBC and ITV networks in the two nations.
Arrangements were expected to be made in Northern Ireland nearer the time.
Early reaction mixed
The broadcasters gave the parties until the end of January to respond, but the early reaction was mixed.
The Liberal Democrats welcomed the plan as fair and necessary, but the Tories raised questions over whether the Liberal Democrats should be included.
Tory Party chairman Michael Ancram said: "It remains the wish of the Conservative Party that there should be a series of debates between the leaders of the two main political parties, with involvement for the Liberal Democrats, though not in a three way format."
Labour says idea 'interesting'
A Labour Party spokesman said the "interesting" proposal would be carefully considered.
Margaret Beckett, Labour's leader of the House of Commons, said it was up to Mr Blair to decide, but added: "I am very mindful of past precedents. It has never happened before. Is it a good idea? Very interesting question."
The prime minister's official spokesman has already hinted that Mr Blair would be willing to take part.
Asked about the possibility recently he said he had a "hunch" the debates would take place.
'Three key subjects'
Plans for live debates before the 1997 election were scrapped after disagreements over the format they should take.
In the proposed debates, each broadcast would cover three key subjects, with each man making brief opening and closing statements.
An independent opinion-polling organisation would select a representative studio audience, who would be able to applaud but not ask questions from the floor.