In the summer of 1985, when I arrived in the capital of the United States, The Washington Post was one of the finest newspapers in the country. Ben Bradlee, its executive editor, who was best known for driving coverage of the Watergate scandal of just a decade earlier, dominated the newsroom with his gravelly voice and infectious smile. Even the lowliest copy boy called him "Ben". Everyone was committed to producing a great paper, around the clock, seven days a week.

I had joined the paper as the sixth Laurence Stern fellow, an annual prize bestowed to a young(ish) British journalist in honour of Larry Stern, a former Vietnam war correspondent and national editor who died, prematurely, while jogging on a beach in Cape Cod, in 1979. Bradlee, a close friend of the anglophile Stern, elected to create a fellowship in his name.

Entering the Post newsroom was like walking on to the set of All the President's Men , the 1976 film starring Robert Redford and Dustin Hoffman as the Post's own Bob Woodward and Carl Bernstein, with its row upon row of reporters, each with their desk-top computers. (At the FT, we still bashed away on typewriters.) Bradlee's glass office stood in the centre of the newsroom. Woodward's investigative team was tucked away at the back. There was a swagger about the place that was irresistible.

To spend time as a reporter on the national staff was to experience a rigour that was bracing - and unfamiliar. "Good story," growled Mike Getler, foreign editor, reading my first front page piece, "but you need to be more precise about your sources." Phrases such as "it is understood" and "people close to the situation" - all grist to the mill in Fleet Street - failed to cut the mustard on 15th Street in DC.

Reporters were given days, often weeks, to research stories. The editing process was exhausting: copy passed through at least four pairs of hands. The other eye-opener was the access that Post journalists enjoyed. A fat Federal government directory provided telephone numbers for officials, high and low. More often than not, they answered the phone. This was heady stuff for someone used to having Whitehall doors slam shut. At the end of my fellowship, I wrote a commentary headlined "America, you have wonderful bureaucrats . . . "

In retrospect, however, the Watergatescandal was a curse as well as a blessing for US journalism. In 2002, Jonathan Yardley, a Post columnist, noted how All the President's Men made celebrity a goal to which many journalists now aspire. Boys on the Bus , Timothy Crouse's account of how the press covered the 1972 presidential election when Richard Nixon trounced George McGovern, may have had a broader and deeper effect: "It turned the eyes of the press on the press itself," Yardley wrote, "and opened the way to the age of media self-absorption."

Writing in The New Yorker in March this year, Eric Alterman went further: "As the profession grew more sophisticated and respected . . . top reporters, anchors and editors naturally rose in status to the point where some came to be considered the social equals of the senators, Cabinet secretaries and CEOs they reported on. Just as naturally, these same reporters sometimes came to identify with their subjects, rather than with their readers."

An earlier generation of ink-stained newshounds saw life differently. Like the iconoclastic investigative journalist IF Stone, they saw it as their duty to expose establishment wrongdoings. The reflex reaction of the new journalism, however, has too often been a defensive crouch. Or how else to explain the uncritical acceptance of the Bush administration's case for invading Iraq, based on bogus claims that Iraq possessed weapons of mass destruction?

Most damaging, the mainstream press lost touch with its audience at the very moment when technology, via the internet, was dramatically lowering the barriers to entry. Whether this was an unhappy coincidence or complacency is unclear. What is undeniable is that public trust in newspapers started to slip, to the point where a recent study by Sacred Heart University shows barely one in five say they can believe "all or most" media reporting (well below comparable British figures).

According to Michael Elliott, the British-born editor of Time's international edition who has spent almost 20 years working as a journalist in the US, the decline in US journalism can be summed up thus: a broken business model overly reliant on classified advertising revenue that has now moved online; a mistaken notion that post-1945 newspaper staffs of 800-plus journalists were the norm rather than a historical aberration; and, crucially, a stultifying failure to innovate because of the lack of competition.

"The mainstream press in America is so conservative," Elliott says. "Where are the DVD giveaways, where are the special promotions like in Britain? Look at the sports pages! They write about sport like they do City Hall. Where is the sense of fun?"

Elliott attributes the lack of playfulness to "the terrible burden" of living up to the demands of the First Amendment, which guarantees free speech under the US constitution. At its best, it imbues every American journalist with a sense of moral purpose that views journalism as a civic duty; at its worst, it has encouraged a stuffy self-importance.

The contrast with British journalism is irresistible. At its best, the UK press is a riotous carnival offering a panoply of news and views. Obsessed with celebrity and often oblivious to privacy, the UK press is part William Hogarth, part Damien Hirst. It can never be accused of taking itself too seriously but it proved far more hard-nosed in its assessment of the case for going to war against Iraq.

In a post to an FT.com debate this summer on British and American journalism, Bill Emmott, a former editor of The Economist, wrote: "The London media . . . is much less professional, much more sensationalist, even in the so-called quality broadsheets . . . and much less scrupulous about sources."

Emmott added a caveat, however. The British media's willingness to blur news and comment has allowed them to be more opinionated and, therefore, more creative than their US counterparts. Thus, The Independent metamorphised into a "viewspaper" with campaigning front pages (though it now appears to be changing back to a more traditional approach). The tabloids have remained in touch with a mass audience, whatever the misgivings of the more politically correct. The Times and The Guardian have experimented with new formats, which in design terms put their American colleagues to shame (with the exception, perhaps, of the pioneering USA Today).

It would be premature to suggest US newspapers are engaged in a last roll of the dice. The arrival of Rupert Murdoch at The Wall Street Journal may herald a bolder approach to design and more mischief in news coverage, though I should probably recuse myself at this point. There are plenty of opportunities for growth, starting with a renewed focus on local news; a more sophisticated blend of online and print content; and a more adventurous approach to what readers and viewers want, particularly younger ones.

Overall, though, it seems undeniable that 2008 - and the coverage of the presidential election - will be seen as a tipping point in American journalism. The imperial status of the mainstream media - the television networks, big metropolitan dailies and lofty commentators - has been shaken. The lay-offs of hundreds of US newspaper journalists are a symptom of a wider malaise. We are witnessing a shift in the balance of power towards new media, with wholesale repercussions for the practice of journalism.

The sea change was palpable at the Democratic national convention in Denver in August. Hundreds of bloggers were present, many enjoying for the first time much-coveted seats inside the convention hall. Close by, the bloggers were installed in a "Big Tent", a 9,000-sq foot, two-storey structure devoted to new media and offering free massages. The mainstream press, one top New York Times journalist sniffed, were obliged to register as visitors before being allowed inside.

The 2008 campaign has already earned the tag "The YouTube election". Mass distribution of images online, exemplified by the wild popularity of hip-hop artist Will.I.Am's pro-Obama music video "Yes We Can", featuring Scarlett Johansson, has revolutionised the terms of political engagement, especially among younger voters. This online impact is also influencing news coverage, thanks to a swelling army of amateur journalists and opinion-merchants. Mayhill Fowler, a 61-year-old blogger from Tennessee writing for The Huffington Post, epitomises the new breed.

It was Fowler who broke the news that Senator Barack Obama had talked about the bitterness of working-class Pennsylvanians who "cling to guns or religion" and xenophobia as a way of coping with economic distress. It was a seminal moment that foreshadowed the Republican onslaught against Obama as an Ivy League elitist. Fowler later unleashed a second storm by reporting Bill Clinton's "scumbag" rant against a Vanity Fair reporter.

Yet, by her own admission, Fowler only gained access to Obama's meeting at a private mansion in San Francisco because she was a donor to his campaign. She agonised for four days before posting her scoop on The Huffington Post website. At the Clinton rally, her status was equally ambiguous. She failed to introduce herself as a reporter when she asked innocently: "Mr President, what do you think about that hatchet job somebody did on you in Vanity Fair?"

Fowler has no specialist training. She is one of several hundred "citizen journalists" that The Huffington Post - a big media winner this year - has let loose on the campaign under an initiative called "Off the Bus" - an ironic reference to Boys on the Bus . In Fowler's virtual world, traditional journalism has been turned upside down.

Alterman, in The New Yorker, summed up the change: "Whereas a newspaper tends to stand by its story on the basis of an editorial process in which professional reporters and editors attempt to vet their sources and check their accuracy before publishing, the blogosphere relies on its readership - its community - for its quality control . . . Only if a post is deemed by a reader to be false, defamatory or offensive does an editor get involved."

As an editor myself, I find this prospect alarming - not so much because it threatens to put me (and many colleagues) out of a job but because it signals a departure from an honourable tradition in which professional journalists do their best - through a process of discovery relying on multiple sources - to establish something approaching a rough historical record.

The question is whether this same journalistic rigour can survive the current maelstrom. In Denver, it was striking how the television channels, particularly cable, were happy to draw on partisan political consultants - Democratic and Republican mercenaries from earlier campaigns - to fill the airwaves. Seasoned political journalists, once viewed as impartial oracles, were left on the cutting room floor.

In the new world of citizen journalism, the role of the trained journalist as trusted intermediary no longer holds. Some may argue that this privileged status was always precarious, even a fiction. Perhaps there is no such thing as a neutral filter or objective truth, and (print) journalists were imposters to suggest as much.

Yet to abandon the quest to write the first draft of history carries risks. There will always be powerful forces seeking to suppress injustice or inconvenient truths. For all their failings, newspapers, especially the wellfinanced family-owned newspapers, have served as a counterweight. On both sides of the Atlantic, the line between news reporting and comment is becoming increasingly blurred. That is something that should give everyone in the profession pause for thought.