St Petersburg, Brussels - Capping a miserable G8 summit for Tony Blair, President George Bush has spurned an offer from the Prime Minister to go to the Middle East as a peacemaker, after deciding that he would rather send the US Secretary of State, Condoleezza Rice.

The snub was revealed in a private conversation that was accidentally broadcast yesterday. It is the latest in a series of frustrating setbacks that bedevilled Mr Blair, as he spent the weekend trying to reprise the role of world statesman that he played successfully at the Gleneagles G8 meeting last year.

This year's gathering in St Petersburg, which ended yesterday, has seen Mr Blair struggling to make any headway on the two issues, climate change and world trade, that he wanted to push to the forefront of the agenda.

The Prime Minister has also thrown his personal authority behind a proposal to send an enlarged UN force into Lebanon, but yesterday he confessed that it was an "open question"as to whether it will ever happen, with other powerful nations clearly sceptical about the idea.

His unguarded chat with the US President provided a unique insight into the relationship between the two men, from George Bush's opening line - "Yo, Blair. How are you doing?" to his use of a mild expletive to describe the morass in the Lebanon.

They were talking before the start of yesterday's working lunch in St Petersburg's Konstantinovsky Palace, unaware that they were being overheard halfway round the world by a technician who was up early monitoring a live feed for an American TV station. By the time Mr Blair spotted the live microphone, the two leaders had unwittingly shared their private thoughts with the outside world - and revealed who is the boss.

A transcript of their conversation, compiled by Sky News, showed how Mr Bush simply blanked out the Prime Minister's suggestion that he visit the Middle East, telling him: "I think Condi is going to go pretty soon."

Mr Blair tried again, suggesting that the Americans could not afford to have their Secretary of State go into the region and come away empty handed, whereas, he said, "I can go out and just talk." At his press conference later, Mr Blair confirmed that the trip was off.

Mr Bush also revealed his frustration at other governments for not leaning heavily enough on the Syrians, which both leaders suspect of being able to control Hizbollah. "What they need to do is to get Syria to get Hizbollah to stop doing this shit," he remarked.

The rebuff by Mr Bush in this manner was one of several frustrating experiences for Mr Blair during the three-day summit.

Climate change, which Mr Blair sees as the most important long-term problem facing the planet, was mentioned only in passing in a summit dominated by the Middle East crisis and by two powers - the US and Russia - with vast energy-producing interests that they want to protect. But when the Prime Minister reports back to the Commons today, he is expected to emphasise that every head of government in St Petersburg acknowledged that climate change needed to be addressed.

His mild expression of concern about civil rights in Russia was brushed off twice by President Vladimir Putin. First, with a joke at the Prime Minister's expense about the recent arrest of his friend, Lord Levy. Then later with an attack on the UK Government for failing to extradite a Chechen rebel, Akhmed Zakayev, whom the Russians want to put on trial for alleged terrorist offences.

Until yesterday's working lunch, Mr Blair also feared that his efforts to revive talks on a world trade deal had reached a dead end. In his private conversation with George Bush, he is heard saying "maybe it's impossible". But at his press conference later, he said his hopes of success had been restored by the lunchtime discussion, chaired by the German Chancellor Angela Merkel, in which all the protagonists seemed to agree that it was necessary to compromise.

But Mr Blair still risks being humiliated over his call for a peacekeeping force that would go into Lebanon after a ceasefire has been achieved. Mr Blair wants a multinational force much larger than the present contingent of 2,000 Ghanaian and Indian troops on the Lebanon-Israel border. But his hand is weakened by his reluctance to send in any British troops. European foreign ministers backed the principle of an international force, though no clear plan for a mission has yet been tabled.