LONDON -- When the Independent Broadcasting Authority, Britain's commercial television regulatory body, recently sent out a questionnaire to survey viewer opinion about the nine television series deemed the "most violent" on the air here, seven of the shows were U.S.-made.

From "Miami Vice" to "Magnum, P.I.," "The Equalizer" to "The A-Team," the list was a catalogue of murder and mayhem in the streets of America. The IBA expects that this survey will confirm the results of previous polls showing the American shoot-'em-ups to be among the most watched fare on British television.

But despite their popularity, violence-packed U.S. adventure shows may soon become a thing of the past here. Prime Minister Margaret Thatcher, whose government has drawn a correlation between television and antisocial behavior, has asked broadcasters to adopt more "responsible" attitudes toward televised sex and violence, and has promised to create a new watchdog agency to monitor "offensive" broadcasting.

The government and conservative groups such as the National Viewers and Listeners Association, led by feisty septuagenarian Mary Whitehouse, say such an agency is necessary in part because the British public, unlike Americans who can pressure sponsors to stop supporting programs, is at the mercy of the networks.

The state-owned but self-governing British Broadcasting Corp., which operates two of Britain's four channels, has no commercial sponsors. Although the IBA's two channels do run commercials, advertisers can only buy blocks of time and have no say over which programs they accompany.

Both the IBA and the BBC say their surveys have indicated that the vast majority of viewers are neither offended nor influenced by the violent programming, which they can clearly identify as television fantasy.

The Thatcher government, some broadcasting officials here hint darkly, may be looking for a scapegoat for the apparent failure of its tough law-and-order policies. "They spend a lot on the police, and the crime rate goes up," said one official who declined to be named. "It makes good sense to blame TV for something they haven't been effective in curbing."

The networks also argue that they do screen programs for gratuitous violence. The BBC, for example, refused to show four recent episodes of "Miami Vice."

But the case for further curtailing such programs gained new currency here last August when a real-life madman went on a shooting rampage in the small town of Hungerford, killing 16 people.

The man, Michael Ryan, was dressed in a combat jacket and headband, and walked calmly down the village's main street with a semiautomatic rifle in each hand. It seemed clear that Ryan was imitating the movie character Rambo in the film "First Blood," which was shown on television here last year.

While Hungerford was still fresh in the public mind, the independent network last month broadcast the U.S.-made mini-series "Sins." It showed, among other things, the beating of a pregnant woman and the rape and torture of a 13-year-old girl.

"Sins," which caused barely a ripple when it was first shown in the United States in early 1986, brought a flood of public protest here, because of its content and because it began more than a hour before television's self-imposed 9 p.m. cutoff for "family viewing." The IBA publicly apologized, agreeing that the timing of the program was a mistake.

Last week, Home Secretary Douglas Hurd called IBA Chairman Lord Thomson and BBC Chairman Marmaduke Hussey to a meeting on televised sex and violence. As a result, Thomson said the IBA would immediately cut the level of foreign programs, most of them American, shown during peak viewing hours from 5 1/2 to four hours a week.

Hussey said the BBC would thoroughly review its monitoring system for imported programming.

Britain may have only itself to blame for certain types of programming. Nudity, fairly explicit sex and coarse language, far beyond the levels seen in the United States, are relatively common fare in local productions, particularly in late-night time slots.

But when it comes to televised violence, most of that shown here is made in the U.S.A.

No one claims that all American shows are violence-prone. Among the most perennially popular programs here and elsewhere in the world are glitzy soap operas such as "Dallas" and "Dynasty." But if television is their only guide, most Britons could be forgiven for thinking that all Americans are extraordinarily rich, carry their own guns, or both.

A lengthy independent study on television violence in Britain, commissioned by the BBC in 1986 and released in August, concluded that American programs shown here contained more than three times as many "violent acts per hour" as British-made programs.

When matched by genre, the study found that differences between American and British programming narrowed slightly. Thus, while 43 percent of all British dramatic fiction, cartoon and comedy programs contained some violence, 67 percent of similar American programs did. A whopping 81 percent of American feature films on television were found to contain violence, however, compared to 46 percent of British films.

Overall, Britain broadcasts relatively fewer American shows than many countries in Europe, with imported programming comprising only 14 percent of the total. Both the BBC and the independent production companies that provide programs for the commercial stations turn out prodigious amounts of their own material, including stylish series such as "Brideshead Revisited" and "The Jewel in the Crown" that are sold to the United States.

But just as "Miami Vice" may not be representative of the bulk of American programming, neither is "Brideshead" the standard homemade product, much of which would likely put the average American viewer to sleep.

In addition to enviable plays, nature and current affairs programs usually found only on educational stations in the United States, a typical prime-time evening in Britain also includes several hours of coverage of minimally active "sports" such as snooker or darts, boisterous live entertainment hours with a preponderance of bathroom humor and domestic made-for TV films such as "Claws," a BBC offering at 9 p.m. last Sunday.

"Sukey is a beautiful Albanian Brown kitten," the program guide to "Claws" explained, "the sort that anyone would fall in love with. Sylvia Mortimer does -- and so enters into the blue-rinsed world of pedigree cat-breeding, where competition is cutthroat and competition knows no bounds."