LOS ANGELES- Tired from her shift at a strip club and in need of a heroin fix, Sharon Mitchell was about to turn the key in her front door on a March night in 1996 when a man sprang from the darkness and grabbed her by the throat.

Pushing her inside, he crushed her larynx, sank his teeth into her cheek, broke her nose and raped her. Choking on her blood, she managed to knock him out with a 10-pound dumbbell. It was then that she recognized him as the man who, obsessed with her pornographic movies, had heckled her earlier at the strip club.

“That was the wake-up call from the universe, the moment of clarity,” Dr. Mitchell said in an interview. “I didn’t want to be standing on the side of a freeway some day, holding a cup.”

She got off drugs, kept her clothes on and went back to school for a doctorate in human sexuality. Then, 22 months after the attack, she founded the Adult Industry Medical Health Care Foundation, which every month tests about 1,200 sex-video performers for sexually transmitted diseases.

In recent weeks, as the multibillion-dollar sex-film industry here has been brought to a standstill by an outbreak of H.I.V., Dr. Mitchell, 46, has become the most prominent figure in the unfolding story. Scores of actors have flocked to her clinic to be tested, at her insistence.

“This whole thing has knocked 10 pounds off me,” Dr. Mitchell said in her tiny office, as she unwrapped a chocolate bar and simultaneously fielded telephone calls, e-mail messages, and questions from a Swiss reporter and four staff members.

As of Sunday, five sex-film actors here have been told they have the virus that causes AIDS.

The H.I.V. outbreak, the first in the industry in Los Angeles in six years, was traced to an actor who apparently contracted the virus while working on a film in Brazil in early March and who passed it on to at least three actresses here. The fifth case apparently originated in New York and is unconnected, Dr. Mitchell said.

When the outbreak was first made public, Dr. Mitchell and her organization called for an immediate halt to filming. Production is not expected to resume until at least June 8. Her clinic was able to trace the sexual contacts between the two actors who initially tested positive and almost 60 other performers. She said all will be tested for H.I.V. at least three times over two months. Potentially, the number of actors exposed could be large, given that they sometimes perform three or four scenes a day, often with multiple partners.

“Everyone’s been contained,” Dr. Mitchell said. “We’re not looking at a lot of people out there working and spreading disease. If we had not put everyone on quarantine so early, this would really have spread.”

An adopted, only child raised as a Roman Catholic in the farm country of Monmouth County, N.J., Dr. Mitchell was an Off Broadway actress and dancer she toured with the Martha Graham company before starring in hard-core movies in the mid-1970’s. It was, she acknowledged, a radical, liberating rupture from her upbringing.

“I was quite proud,” she said of the moment she first saw herself 16 feet high on a screen.

“The worst thing you could get in those days was crabs or herpes, and that was few and far between,” said Dr. Mitchell, who was briefly married at 17.

Drugs were a different matter. Dr. Mitchell delved into heroin, she said, an addiction that would last nearly two decades. “People I worked with knew I was an addict,” she said. “I never felt it necessary to hide it.”

Working in the sex industry was exhausting, she said, and heroin helped her cope. “The trauma on the body is too much and the whole thing created personal problems, relationship problems,” she said. “It was hard to say, `Honey, I’m going to have sex with a girl, two guys and six rhesus monkeys and what do you want for dinner?’ ”

Dr. Mitchell who legally changed her last name in 1975 in homage to Martha Mitchell, the outspoken wife of Attorney General John N. Mitchell in the Nixon administration made some 1,000 sex movies over 20 years, including 38 that she directed.

She fondly recalled starring roles in “Captain Lust and the Pirate Women” and “Sexcapades,” among others. She also had bit parts in mainstream films like “Tootsie” and “The Deer Hunter,” and played a nurse on the soap opera “The Edge of Night.”

By all accounts, Dr. Mitchell’s transformation from sex-film star to white-coated doctor could not be more profound. On her office door, a sign says, “Well-behaved women rarely make history.”

Though many sex-film performers were casual, at best, about getting checked for H.I.V. years ago, the situation seems markedly improved under the monthly checkups instituted by Dr. Mitchell, who has recorded just 11 H.I.V. infections in the industry between the clinic’s founding in January 1998 and the outbreak last month. By contrast, about 40,000 new cases of H.I.V. are reported annually in the United States, she said.

Health officials appear to have left Dr. Mitchell largely to her own devices, though the latest outbreak is giving them reason to reconsider.

Jonathan E. Fielding, director of public health for Los Angeles County, said his office was investigating whether the clinic was following proper procedures and whether the virus had spread from workers in the industry to people outside it.

“Most of the oversight is by the industry itself,” said Paul Koretz, a California Assemblyman whose district includes parts of the San Fernando Valley area, where the industry is based.

“But it’s not foolproof,” Mr. Koretz added, referring to the clinic’s approach.

The industry employs about 6,000 people and churns out about 4,000 videos a year. Economists here estimate that it brings in as much as $9 billion a year.

As the industry watchdog of well-being, Dr. Mitchell also acts as something of a detective, investigating the origin of each infection and badgering performers who were exposed to come in for testing. Since the outbreak, dozens of names the performers almost invariably use stage names have been posted on the clinic’s Web site, along with their date of exposure and whether they have tested positive.

Not everyone cooperates. One of 12 actresses who had sex with the first performer to test positive in the outbreak ignored requests to be tested, Dr. Mitchell said. Last week, Dr. Mitchell and her assistants tracked the actress down in Las Vegas.

Dr. Mitchell offered her $500 in cash to be tested and the actress accepted. “Whatever works, right?” Dr. Mitchell said.

She was also looking into rumors that some performers on the quarantine list had gone back to work before learning whether they had been cleared.

“This is a very difficult population to deal with,” Dr. Mitchell said. “I’ve had to battle more within the industry than without.”

In the hot afternoon, actresses, most in platform sandals, tank tops and miniskirts, strolled into the clinic’s storefront waiting room on Ventura Boulevard. Tattoos and pierced noses and navels abounded. One girl, sullenly filling out a form before her H.I.V. test, wore a T-shirt that said, “Wasn’t picked for cheerleading.”

Another actress, Monica Bailey, 20, did not seem to mind the $110 cost of an H.I.V test.

“It’s way worth it,” Ms. Bailey said. “I can go to a regular doctor and get it done, but it’s nice to come here and it’ll be ready in two days. I encourage my friends to come here. They’ll set you straight.”

During the production hiatus, Ms. Bailey said, she has been working at the Frisky Kitty as a stripper and doing a little filming, but acting opposite women only, not men.

“Everything was going so well,” she said, “that something like this was bound to happen.”