He swears like a docker, berates his viewers, and mocks his president. So why has Jon Stewart been handed a show with a global audience of 160 million?

It is CNN on Saturday night and Jon Stewart cuts to his man on the spot in Baghdad for a situation report. He then switches to his man on the ground in North Korea. Baghdad guy suddenly gets angry. "Iraq is way more important than Korea," he whines. "Cut back to me." We can hear him in the studio. The guy in North Korea can hear him, too. "No way," he comes back. "At least North Korea actually has weapons of mass destruction." Within seconds, they are squabbling for airtime until Stewart pulls them both off air and returns to the bulletin, which seems to consist entirely of gaffes that President Bush has made in his speeches this week.

If this sounds more like Chris Morris and The Day Today than the prime time output of a respected international broadcaster, you are only half wrong.

Jon Stewart is the host of US cable network Comedy Central's The Daily Show, probably the most irreverent and certainly the most foul-mouthed of the late night talk shows in the Letterman mould that dominate post-10pm viewing.

Stewart is different in two ways; first, he does more sketches and routines than interviews, and second, he has been signed up by CNN International to do a weekly "best of" programme that will be broadcast to CNNI's 160 million viewers worldwide. The Daily Show With Jon Stewart - Global Edition goes out at 11.30pm on Saturdays and Sundays nights in every CNNI territory.

At times, it is difficult to believe that they have actually let him on air. He swears like a docker - in one curiously cute interview with Cameron Diaz they struggled to outdo each other with the number of "motherfuckers" they could say - and spends the final couple of minutes of the show berating his CNNI viewers. "You're in a hotel room in a foreign country on Saturday night. What are you doing watching me? At least go out and get a latte."

"We do set some boundaries, but he pretty much has licence to do what he wants," says Rena Golden, executive vice-president and general manager at CNN International. "His producers go through the week's shows and put together the 'best of' package and we usually just let it go out as it comes - although I do have licence to bleep."

Perhaps there is a strategic reason for this liberal approach. If 1991's Gulf war was seen as CNN's war, the news provider honours in the Afghan conflict went to Qatar-based Al-Jazeera. Immediately after September 11, CNNI was running US CNN's feed, which was about as draped in the Stars and Stripes as it is possible to get. Some observers feel that CNNI lost some of its impartial reputation. Critics have accused it of being too pro-American for an international channel. Is Stewart, who lambasts George Bush more effectively than any British satirist, their answer to the critics?

"Jon's show is not an attempt to redress any balance," Golden insists. "I think people's perception of CNNI lags behind the reality. International has a completely different perspective from the domestic station. Jon is on because he hits our demographic - young and intelligent - and because at the weekend our viewers stay with us for longer so we don't just give them rolling news."

Stewart's daily template for CNNI's weekly programme, The Daily Show, has been described by US Esquire as "to current comedy what Saturday Night Live was to 70s comedy". He also picked up an award from New York magazine in December 2001 for his wry approach to 9/11. Inevitably his CV includes time as a stand-up and a spell on MTV, which he ditched for a syndicated talk show no one watched. The Jewish comic delivered a Hitler-based sketch that outraged his bosses and promptly got him fired, so when The Daily Show came along it saved him from hanging out in Hollywood and being edited out of The First Wives Club.

As the Guardian's transatlantic call connects for our interview, the woman from CNN chirrups, "Hi Jon, it's CNN here." "Are we at war yet?" he barks. "No, not yet Jon," she replies, unsure if he's joking. "Well, let me know when we are, OK?" "OK, sure," she falters and the interview begins.

"I see myself as a driving force for global peace," he deadpans instantly. "Since we have been on CNNI, the border between India and Pakistan has been stood down from red alert. Coincidence? We're bringing healing to the international community."

He speaks at high speed, jumping with gags whenever possible. His show pokes fun at Bush a lot. "Well, you're seeing the edited highlights," he cuts in. "Our seven minutes of news on Staten Island won't play in Burundi. No, don't say that. Say we're a powerful voice of opposition."

Asked about the Chris Morris argument that calling himself a satirist sets him up for the same fall he delivers to world leaders, he becomes serious for a moment. "I don't set out to satirise as an end in itself," he says. "But when I watch TV these days it makes me crazy. Fortunately, I'm in a position to go into work and do something about it. I can scratch the itch. Not that I'm trying to change things. If my goal was to make a political point, there are people who can do it far better than me, and the audience is watching to laugh, not hear a lecture."

"When we spot silliness, we say so out loud," he continues. "We're not really Democrat or Republican. We're out to stop that political trend of repeating things again and again until people are forced to believe them."

When asked about Martin Sheen's contention that he has come under pressure from the right wing in America because of his anti-war views, Stewart says he has been able to mock the president every night without any similar backlash from advertisers or pressure groups. "But I imagine Martin Sheen has felt persecuted for many years. I mean, he's Charlie Sheen's father."

Besides, he says, he doesn't speak for those with strongly held political views - he speaks for the "politically disappointed". "Liberal and conservative have lost their meaning in America," he says. "I represent the distracted centre." As for his CNNI audience, "I've always assumed they were basically horny salesmen," he shoots back. "You know, the shameful thing is, we're in 140 countries with this show now and I've been to two of them. And one of those is Bermuda."

At the end of the interview, the Guardian stays on the line while Stewart asks the CNN woman how the show is going. Out of character, he sounds far less sure of himself, gratefully lapping up the nuggets of praise she tosses him. "It's so hard to know how the show's going down," he says, ruefully. She tells him they've been getting 20 to 30 emails of praise a week, mainly from expat Americans and many of them from Germany.

"Right," he seems perplexed. "From expats, right?" "No," she tells him. "These are from German Germans. They really like the show. I think it's to do with the anti-war thing." There is a long pause. "Huh," he says, for the first time completely lost for words.