The most dramatic story on BBC television's showpiece nine o'clock news Monday night was not the insurrection in South Korea, the manhunt for the murderer of a retired vicar in soutern England or the prison escape of a legendary London gang leader. Instead it was the shooting of a Texas oilman who has become Britain's most popular television villain -- J. R. Ewing of "Dallas."

Staid BBC news televised a replay of the brutal, unsolved crime in the Ewings' penthouse offices in downtown Dallas that about 25 million Britons had watched "live" just minutes earlier. The replay horrified television critics and upholders of the traditional high standards of BBC news, but delighted millions of this nation's incurable "Dallas" addicts.

The important bigger-than-life American series is so popular here that BBC -- fighting a ratings war with the rival commercial television network -- held back this season's climactic episode for Monday night's spring holiday prime-time viewing, two months after American television viewers had already witnessed the shooting.

BBC was rewarded with an audience amounting to nearly half the country's population. Pubs, restaurants and highways emptied as "Dallas" fans flocked faithfully to their tellies.

After offering odds on which of J. R.'s enemies had finally decided to do him in, the William Hill chain of betting parlors (gambling on everything is legal in Britain) has been inundated with small wagers totaling more than a quarter of a million dollars by yesterday afternoon.

"Dallas Fever!" proclaimed yesterday's banner headline on Britain's largest selling newspaper, the Rupert Murdoch-owned tabloid Sun. Most of its front and two other pages were devoted to the "Dallas" phenomenon, including three stop-action photos of the shooting and an editorial cartoon in which a bedside Ronald Reagan is comforting the fallen fictional oil baron in his hospital room and pleading, "Don't die, J. R., I want you for vice president."

"Who shot J. R.?" was also a big story in Britain's other three national tabloids. But the Times, the stiff-upper-lipped "noticeboard of the establishment," ignored this social uprising. And the television critic of the equally highbrow Guardian scolded, "I have a message for BBC news: 'Dallas' is not real."

But "Dallas" extraordinary hold on the British public is measurably real. Its audience grew steadily over the past two years until it regularly topped 20 million for each episode this spring in a nation of 56 million people. BBC spokesmen said their switchboards were literally overloaded Monday by callers demanding to know who shot J. R., and when the series would reappear in the autumn.

Actor Larry Hagman, who plays J. R., was voted this month the top-drawing male character on British television. He was mobbed by newsmen and fans on a recent publicity tour here, during which his white Stetson hat, cowboy boots and gold-plated walking stick became as familiar as Churchill's cigar. Gossip columns have been filled with eccentric details of his jogging, dieting, wearing of disguises and refusal to speak to anyone on Sundays.

Hagman told British reporters from his home in Malibu Beach, Calif., Monday that "As far as I know the scriptwriters haven't yet decided themselves" who shot J. R. "It's not something I'd bet on," he said.

British bettors have put a lot of money on a "Dallas" character who was supposed to have been killed in a plane crash this season, Dusty Farlow, the rich cowboy lover of J. R.'s long-suffering wife, Sue Ellen. He's now the six-to-four favorite as J. R.'s assailant, according to bookmakers at William Hill.

J. R.'s sister-in-law and jilted mistress, Kristin, and cheated business associate, Vaughan Leland, are next at four-to-one odds. Fading fast is Sue Ellen herself, now a 16-to-one long-shot, apparently because she became too obvious a suspect. The fast-closing dark horse is J. R.'s devoted, soft-spoken mother, Miss Ellie, now at six-to-one, apparently because so little suspicion had been thrown on her.

The William Hill spokesman said there has been "absolutely phenomenal interest" in what the betting shop chain began as a lark. "We've offered odd bets before like when it would rain again, when it would stop raining, whether it would snow on Christmas or whether the tunnel under the English Channel would ever be built, but we've never had a response anything like this.

"I think people are tired of Olympics boycotts, Iran sanctions and Afghanistan. They were ready for the old-fashioned escapism that 'Dallas' has given them."

Popular disc jockey and talk show host Terry Wogan, who for nearly two years had been rehashing 'Dallas' the morning after with his listeners, is a little contemptuous now that everyone else in the media has caught on. "I give it one more season now," Wogan said yesterday. "Then it will be all over."