That staple of America's mornings, breakfast television, has finally arrived in Britain. While the accents may be different, the breezy blend of information and froth offered is proof again that imitation is the sincerest form of flattery.

The tempo, contents, graphics, even the program names are basically interchangeable with their transatlantic counterparts. No surprise, therefore, that the "Today" show's Jane Pauley, appearing on one broadcast, pronounced it "gangbusters."

After months of preparation amid enormous publicity, two separate but similar undertakings have been launched in the past two weeks. From 6 a.m. to 9:15 a.m. viewers now have a choice of the BBC's "Breakfast Time" or commercial television's TV-AM, whose main program is called "Good Morning Britain." It premiered today.

Genial and chatty hosts--David Frost of TV-AM is the only one well-known to American viewers--are ensconced in living room-style sets parlaying a stream of guests and regular performers as wrap-arounds for frequent and repetitious bulletins of news, weather and sports. There are health tips and astrology, television previews and gossip. Items rarely run longer than five minutes apiece.

The mood on the BBC show, in particular, is as determinedly cheerful as any of the giddy-talk local news shows in the United States. Only minutes into one morning's program, for instance, after the newsreader's once-over-lightly about a national water workers' strike and the Geneva arms talks, hostess Selina Scott hastily assured viewers that all "won't be gloom and doom." Then she introduced two music hall comedians and their St. Bernard, who spent much of the time in banter about how sleepy they were.

"Breakfast Time" is a far cry from the BBC tradition of its early years when radio announcers donned tuxedos to deliver the news. Frank Bough, the principal male host, wears cozy-looking cardigans, while the astrologer wears an outfit that has the shape of a brightly colored circus tent. "Relaxation" is the keynote of the enterprise, according to its editor, Ron Neil.

By contrast, TV-AM seems more earnestly ambitious perhaps because, unlike the BBC program, it is not part of an already substantial news enterprise. For its opening show, "Good Morning Britain" commissioned a national poll showing unemployment as people's greatest worry, and then Frost did a hectoring interview with the government minister mainly concerned with the problem.

The company was started from scratch three years ago. The chairman is 46-year-old Peter Jay, a former journalist who served as Britain's ambassador to the United States in the late 1970s. He, Frost and the four other cohosts (including Robert Kee, whose widely admired series on Ireland was a PBS success last year) are all investors, along with several banks and institutions. Their success will depend strictly on advertising revenues, a cause for concern because of a long-running dispute over commercial residuals between the actors' union and advertisers.

One novel aspect of the programming is that it also will appear in weekend versions, with an emphasis on leisure and children as well as the usual mix. With more than 20 hours a week of live broadcasting to prepare, the hosts are scheduled in rotation so that each is on the air about six months a year.

The studios and headquarters of TV-AM, a mile or so from central London, are in a sprawling, $20 million glass-and-steel structure with the sort of jazzy atrium, open work spaces and hanging walkways that accentuate the program's American feel. One madcap touch are five-foot egg cups arrayed along an outer wall, on the odd chance someone might otherwise miss the breakfast imagery.

Whereas "Breakfast Time" can rely on the considerable news resources of the BBC should it choose to do so, TV-AM has created its own news team mostly by recruiting hundreds of younger people eager for a shot at the big time. The company also has access to ABC's overnight news from New York but none of it seemed in evidence today.

Many skeptics have predicted that breakfast television will draw small audiences here for several reasons: British sets usually aren't in kitchens; the BBC's morning radio is still excellent; the country has the highest per capita newspaper readership in the world, and, on balance, the British are resistant to change.

Peter Jay strenuously disagrees. "It is a peculiar national vice," he says, "that we have to pretend anything new is not going to happen." Even the pervasive British tea bag, he contends, was once dismissed as a nonstarter.

Early returns, at least for the BBC program's initial weeks, show that audiences could turn out to be considerably larger than even optimists predicted. An estimated 8 million people a day watched, according to a national survey, compared with 5 million forecast for the two programs combined. "The Jeremiahs who said there wasn't an appetite for 'Breakfast Time' have been proved wrong," said the BBC's Neil.

BBC's "Breakfast Time" apparently is off and running. But for the self-sustaining TV-AM organization, with a substantial financial risk at stake--aside from some considerable professional reputations--there is still going to be some holding of breaths.

"We spent three years making the debut program," Peter Jay said today. "We have 24 hours to make the next one."