The British Broadcasting Corp. was plunged into its second serious controversy in less than a month as its management today confirmed weekend newspaper reports that for decades it has allowed MI5, Britain's internal security service, to screen BBC employes secretly for suspected security risks.

A statement issued after an emergency management meeting said the practice was introduced "at the request of the BBC in 1937 and has continued under successive administrations." It said that "only relatively few members of staff go through this procedure; they are necessarily involved in sensitive areas, or require access to classified information."

In a front-page story yesterday, The Observer listed eight cases in which employes or potential employes had been turned down for promotions or jobs based on security checks of which they were not told. All eight were blocked following MI5 allegations that they had leftist sympathies.

On Aug. 7, BBC television and radio news staffers staged a 24-hour strike to protest the cancellation of a television documentary about Northern Ireland after the government had charged that it gave "succor" to terrorists.

Although state-owned, the BBC operates under a charter that assures it independence from government interference. Despite government insistence that its "request" for the show's cancellation did not amount to censorship, journalists said their independence and integrity had been compromised.

The revelations about the screening, or "vetting," procedure have added fuel to those charges. In a news conference today, Harry Conroy, secretary general-elect of the National Union of Journalists, said the union was "not opposed to all vetting; many employers vet potential employes. But we are opposed to vetting in secret that doesn't allow the person who has been vetted to examine the evidence against him and perhaps correct any inaccuracies."

"And also," Conroy said, "we do wonder why the state security service should be involved in the BBC."

The union asked for meetings with BBC management and Home Secretary Leon Brittan, in charge of law enforcement and broadcasting regulations. The Home Office said that Brittan is on vacation and that it would not comment on "security matters."

Opposition politicians today harshly criticized the vetting policy and indicated that they would bring it up for debate when Parliament reconvenes in October.

Among the examples listed by The Observer and confirmed today by former BBC officials, journalist Isabel Hilton was vetoed for a BBC television job in Scotland in 1976 because MI5 said that she was an organizer of a pro-Chinese group, the Society for Anglo-Chinese Understanding.

A BBC official later determined that the security report was the result of a clerical error. Hilton, a Chinese linguist, served as secretary of an academic body based at Edinburgh University, the Scottish-China Association. By the time the error was discovered, however, she had taken another job.

In another case, journalist Richard Gott was approved for a job as editor of The Listener, a BBC general-circulation magazine, in 1981. But the decision was reversed after MI5 said Gott was a leftist, was known as a protester against the Vietnam War and had been arrested in Bolivia for publicly supporting Che Guevara nearly 20 years earlier. Gott was not informed of the vetting or the reason for the denial.

Personnel files of perceived security risks already on the BBC staff are marked, Aubrey Singer, former BBC managing director for television, said today. Singer said the system had been "an open secret for years" within BBC management and was begun because of "fear of infiltration" among journalists who reported on sensitive security, defense and scientific subjects.

"I didn't like it," Singer said. "It was deemed by the powers that be to be necessary. In the end, it demeans