Marilyn Chambers, the legendary adult movie queen who was the wholesome model on Ivory Snow detergent boxes in the early 1970s when she made her adult movie debut in the X-rated classic “Behind the Green Door,” has died. She was 56.

Chambers was found unconscious Sunday evening at her home in Canyon Country, said Los Angeles County coroner’s spokesman Ed Winter.

The cause of death is under investigation, but foul play is not suspected and an autopsy is pending.

Throughout the ‘70s and ‘80s, Chambers was one of the biggest names in the porn industry, ranked by Playboy magazine as one of the top 100 sex stars of the 20th century and named one of the top 10 adult film stars of all time by Adult Video News.

“She certainly was one of the first famous porn stars,” said Mark Kernes, senior editor of Adult Video News.

“In her day, there was really Linda Lovelace, obviously for ‘Deep Throat,’ and Marilyn Chambers,” he said.

Chambers’ “Behind the Green Door,” Kernes said, “was made all the more exotic, I think, for some people because she had been on that Ivory Snow box. So here’s the Ivory Snow beauty queen having hard-core interracial sex.”

A fledgling actress, Chambers was living in San Francisco and making ends meet working as an exotic dancer when she saw a newspaper ad seeking actresses for what was described as a “major” motion picture.

It wasn’t until she filled out an application that she discovered the movie was pornographic. The producers -- Jim and Artie Mitchell -- offered her the starring role.

“I thought I’d take a shot,” she explained in a 1977 interview with the Los Angeles Times. “I was intrigued by the story. I really liked the fantasy involved. And I figured it might be my last chance at something really big.”

Chambers had some conditions, however: She insisted that all the actors be tested for sexually transmitted diseases, and she demanded a percentage of the movie’s gross receipts.

The low-budget “Behind the Green Door” became one of the biggest adult movie hits of the ‘70s, having received an unexpected publicity boost shortly after it was released in 1972.

Procter & Gamble, unaware of Chambers’ role in the X-rated film, used one of her photos that had been taken during her New York modeling days on its laundry detergent box -- she’s shown cuddling a laughing baby.

“Timing is essential for someone’s career,” Chambers said in a 2007 interview with Rhode Island’s Providence Journal.

“That’s what did it for me. The controversy of both those things happening at the same time,” she said.

Procter & Gamble, whose Ivory products were “99 44/100% pure,” quickly pulled the boxes from store shelves.

“The media attention of the whole controversy was insane,” Chambers said in a 2003 interview with the Philadelphia Daily News. “This was the first time attention was being paid to erotic films.”

Out of that, she said in a 2004 interview with the Montreal newspaper the Gazette, “came a Marilyn Chambers clause in all modeling contracts, saying that you can never have posed topless or nude or been in any kind of adult film or Playboy or anything like that.”

Chambers followed up “Behind the Green Door” with another hit produced by the Mitchell brothers, “Resurrection of Eve.”

And in 1975, Artie Mitchell produced a semi-documentary, “Inside Marilyn Chambers.”

Chambers reportedly longed for mainstream movie stardom, and she starred in director David Cronenberg’s R-rated 1977 horror movie “Rabid.”

But by 1980, after appearing in a cabaret act as a singer and dancer and cutting a disco-flavored record, she returned to adult films, including “Insatiable” and the film series “Marilyn Chambers’ Private Fantasies.”

“I would have loved to move on,” she said in a 2004 interview. “I’ve been stigmatized, and it’s something that’s very difficult to get out of.”

Chambers stopped making hard-core movies in the mid-'80s, but returned again in the late ‘90s with “Still Insatiable,” Kernes said. “In between,” he said, “she was doing soft-core late-night cable movies.”

Her last screen appearance was in filmmaker Victor Franko’s low-budget independent movie “Solitaire,” which was filmed in Rhode Island in 2007.

In the PG-rated film, which has yet to be released, she plays a Providence police officer in pursuit of a group of teenage petty thieves.

Chambers was born Marilyn Ann Briggs on April 22, 1952, in Providence, R.I., and grew up in Westport, Conn. She became interested in acting as a teenager and began working as a model, appearing in print ads for Clairol shampoo and other products.

After retiring from adult films, Chambers remained a popular draw at memorabilia and autograph shows.

Chambers was married and divorced three times, including a marriage to Chuck Traynor, who had previously been married to Lovelace.

Chambers had a daughter, McKenna, from her marriage to Tom Taylor. A complete list of surviving family members was not immediately available.

dennis.mclellan@latimes.com

Times staff writer Andrew Blankstein contributed to this report.