Though Michaelle Triola Marvin and Lee Marvin were never married, she didn't need a piece of paper to validate her devotion or to ask for $1 million in alimony when the couple split, she said.

Michelle Marvin wants half the property accumulated by the actor during the six years they lived together because, she said in an interview, "I was like a wife to Lee."

A landmark 1976 California Supreme Court decision upheld her right to a jury trial on the matter, and now, for better or worse, the repercussions are rippling across the country. According to attorneys, hundreds of suits applying principles established in the Marvin decision have been set in motion nationwide.

In Michigan, the state Supreme Court classified an unmarried female cohabitant as a dependent and therefore entitled to workman's compensation survivor benefits by virture of her long-term relationship with the deceased.

The Minnesota Supreme Court cited the Marvin decision in ruling in favor of an unmarried woman claimant, while the Georgia high court has denied a claim based on Marvin's decision precepts.

Meanwhile, in Hollywood, the stakes are high.Actress Britt Eklund sued rock star Rod Stewart for $15 million, and a judge permitted her to occupy the singer's mansion while she negotiated reported seven-figure out-of-court settlement. Eklund's case stressed compensation for the business contribution she made to Stewart's career during their 2 1/2-year relationship.

For being by rocker Alice Cooper's side throughout his seven-year ascendacy from an unknown musician to a millionaire, 28-year-old model Cindy Land asks $3.5 million, or half of Cooper's acquired assets during that period.

Actor Nick Nolte was sued for $5 million this spring, after breaking with model Karen Ecklund (no relation to Britt), who had lived with him since 1972. She wants $2 million for her role as companion and confidant, $1 million for damages to her modeling and acting career and $2 million in punitive damages.

Linda Grey, a Hollywood publicist whose clients include Sylvester Stallone, filed suit this month for $1 million from the estate of prominent rock promoter Steve Wolf, with whom she lived for 11 months until his death by gunshots during a robbery at his home last fall.

In one of the most unusual applications of the Marvin decision, a San Diego judge has ordered a lesbian to pay her estranged "wife" $100 monthly support pending a community property trial next year. The couple had lived together less than a month.

"It's a sociological phenomenon that's coming," says Los Angeles divorce attorney Stuart Walzer, who conducts seminars for nonlawyers called "Living Together in California," in the wake of the Marvin decision. And Stephen Waterbury, author of a Harvard Law Review article on the decision, warns that "unmarried people are really up in the air. No one knows where they stand."

"I'm going to put marriage on trial in the Marvin case," promises Marvin Mitchelson, the attorney representing Michelle Marvin, whose court appearance is scheduled for Nov. 30. (He also represents models Ecklund and Lang.)

The sanctity that's been given to the license is religious-oriented. I'm going to show that when people live together, they have precisely and identically the same type of lifestyle as two people who have a license in their drawer, and they should be treated as one and the same."

Already, Mitchelson calls the Marvin decision "a victory for single people" because, in the absence of a written or oral contract between partners, it frees courts to construe "implied contract" or "tacit understanding" based on the "demonstrated conduct" of the couple.

Although Mitchelson includes Sonny Bono and rocker Stephen Stills among his clients, he is known in celebrity circles as a "ladies" lawyer.

Among his famous clients, he lists Sara Dylan (in her reported $12.5-million settlement from Bob Dylan this year), Jacqueline Chase in her present divorce proceedings from comedian Chevy Chase, "the wives of four Academy Awards winners" and, as the headlines in his newspaper scrapbook proclaim, Divorces for Rhonda Fleming! Pamela Mason! and Connie Stevens!

A glossed transparency of Botticelli's "Birth of Venus" is inset in the ceiling overlooking Mitchelson's desk. "She's my official symbol," he says, proudly. Reproductions are everywhere in his office suite. Venus rises even from the ashtrays.

To Mark Goldman, Lee Marvin's attorney from the law firm of Goldman & Kagon, the Marvin decision represents a sorry state of affairs.

"if you want to get rid of a partner, if you want to break up, it's much smoother to be married now, because there are established court procedures. This is a much dirtier fight," he says.

Claiming "companionship cuts both ways," Goldman says a cross-complaint filed by Lee Marvin will ask $1 million from Michelle Marvin, should she win a settlement for her household services to him.

"The claims are getting more and more farfetched," Goldman complains. "These are bedroom contracts. There's never any witnesses. There's never any corroborating evidence. Some of the claims may be legitimate, but there's no way to distinguish the frivolous from the legitimate." '. . . I Did My Part'

"The term professional girl friend comes up a lot," said Cindy Lang, with a shrug, in her first interview about the $3.5 million suit she has filed against Alice Cooper.

The couple met in a Detroit art museum in 1968, when Cooper was an unknown musician who was "basically playing high schools at the time," Lang said. She was an 18-year-old from a "strict Catholic family" preparing to enter a home-town Catholic college as an art major.

"I never believed that he would be a success, but he was the first man in my life, and I just had to take a risk.

"During our first three years, there were highs and lows, but basically we lived on $5 a week. I mean it was no fun. And I did my part. I sold Christmas trees if I had to, to keep us in food."

Eventually, Cooper became a millionaire rock star and, as he has publicly confessed, an alcoholic, recently cured. During the last three years of their relationship, Cooper's drinking made him so ill, Lang alleges, that, "Sometimes I thought he was dying. But as bad as it got, I never walked because that would have been one more reason for him to get drunk.

"The last year that Alice and I were together, we were alone three days. We had bodyguards. We had chauffeurs. We hardly knew what to do with each other. No matter how comfortable you are, you just may not be happy.

"My claim is much more like Britt Eklund's with Rod Stewart. She was supportive, helped his career, helped on the road, helped write songs.

"I was not a wife to Alice. I gave up my career of my own volition. I gave it up because what was more important to me at the time was my man."

When Cooper left her in 1975, she said, "He came to me and promised a house, a car and a small salary until I got on my feet. It was supposed to be a $100,000 home, free and clear." Instead, she said, she was offered a house "with only $10,000 down on it, and not even in my name, but the payments were."

When the woman realtor handling the home purchase advised her to see Marvin Mitchelson instead of signing the papers, Lang said, "We went that afternoon and I came away with Mitchelson as my attorney, even though I didn't have the money to pay him.

Land defends Cooper's "good faith," contending that it was his business representatives who reneged on the agreement after Cooper had left the country.

"At first, I was defensive about the claim," she said. "I was like every other woman. I didn't feel my worth. I found it hard to answer the question, 'What do you think you've done to deserve this figure?'

"I lived with this man for seven years. I thought he worshipped me. All of sudden he leaves me for an 18-year-old girl. Out of our seven-year relationship I was left virtually without a friend. Everybody went to where the bread was buttered, his side.

"Then people I never even knew would call me and say, 'Cindy, this involves all women.' I must say I feel much better about myself since I've exercised my rights. I know this suit could go on for years. I'm not sitting back on my haunches waiting to collect. I'm surviving."

Should Lang win, Mitchelson's firm will collect one-third of the amount in contingency fees. Recently, they crossed one hurdle by successfully defending against motions to dismiss the case by Cooper's attorneys. "The deposition was grueling, all about my sexual life, horrible things you'd never even think of," Lang said.

"I'm doing this because I'm trying to develop law," said the affable, silver-haired Mitchelson. "I'm after a uniform marriage and cohabitation act. I absolutely believe that there will be a decision on this in every state in the next five years, and I believe that I or someone else will take a case like this to the Supreme Court."

Mitchelson sits in a chair flanked by an alabaster statue of a buxom maiden, her nose rubbed snub by time. Based in Los Angeles, he has been admitted to practice law in 10 states and four foreign countries.

There will be plenty of grist for the Hollywood gossips when the Marvins meet in Los Angeles Superior Court Nov. 30 to tell their conflicting stories to a jury. Caring for a 'Baby Chicken'

"Do you know how I took care of Lee?" Michelle Marvin asks rhetorically. "I took care of Lee like he was a baby chicken. People forget that when I met him he was just a working actor. He was not yet the star in pictures that he became."

The stylishly dressed 43-year-old still seems shaken by what happened after Marvin left her in 1970 to marry a high-school sweetheart.

Michelle and Lee Marvin met during the 1964 filming of the movie "Ships of Fools." in which they both had parts. Shortly thereafter, they moved in together though Marvin did not divorce his estranged wife until 1967 Michelle Marvin gradually gave up her performing career when the pressures of attending to "Lee's career became so tremendous, so taxing," she says.

"I was just a young singer, but how will we ever know what might have been?" she says explaning the $100,000 portion of the settlement she asks in compensation for her career.

"But I haven't been the least bit angry up until right now," she says. "It's suddenly all dawned on me what he's up to with this cross-complaint.

"I'll talk - the drinking, it will all come out. It's Lee's own fault that it came to this because in the beginning all I was asking was just some temporary support." Initally, Marvin offered her around $1,000 a month for around five years, she said, but the checks stopped coming a year later. She then went to Mitchelson.

The case's publicity has been damaging and has made it difficult for her to find employment or resume her singing career, she claims.

Recalling her circumstances when the William Morris agency hired her in 1972, her eyes fill with tears. She had been "destitute," she says, and, "When I was at the Morris office, people that I had had at my dinner table as Mr. Lee Marvin would come in and see me sitting behind a typewriter.

"I'd like for this lawsuit to be over because it interferes with my life. The mere mention of my name - court battles, making a man pay for restitution and everything . . .

"Because of me, no man will be able to walk off with the deed to the house. That makes me feel good, but it doesn't make me hate men. I love men, especially gray-haired men.I'm the worst pawn for a silver fox, as I say. And I'll always be that way. I can't conjure up bitterness."

Though Marvin's attorneys claim she changed her name "only after it became apparent to her that the relationship was breaking up," she responds, "It was to Lee's advantage. We traveled a great deal and we felt that if Marvin were on all the passports it would be easier.

"Everything was for Lee, and that's all right. I'll never regret that because that's the way I was brought up. I was pounded into my head, evertything is for the man."

"Lee Marvin has always said that since he and Michelle had both come off previous marriages, neither wanted the responsibility of marriage," said Goldman. "You'd have to be awfully foolish to be suffering all the financial problems of divorce and immediately make a tremendous deal with somebody else for the balance of the property you have left."

Still, Goldman worries, "To what degree are juries going to say in cases like this. 'We feel sorry for this woman. She gave up the best years of her life to this man," and ignore the fact that there was never an agreement between them.

"They'll say, 'Oh, that's nothing to him. He can afford to pay it. She has nothing, and she put in a lot of valuable years. Let's give her a bunch of money.'"

"Even though you got a Marvin-type case, if the guy you got is poor, or even middle class, you might as well forget it," says Stuart Walzer. "The legal costs are devastating."

Cases similar to Marvin may arise indirectly through tax or workmen's compensation or insurance disputes, as Waterbury, the author of the Harvard Law Review article, points out. "In trying to achieve the value of predictability and simplicity. You can protect yourself by writing a non-nuptial or cohabitation agreement, but there seems to be an aversion to that somehow."

Evidently, the version extends all the way to Beverly Hills. "I have a lot of clients who are coming out of marriages and living with another woman, usually a younger woman, who says, 'Hey, I'll have to have you draft me a contract,'" says Stuart Walzer. "But somehow they're all a little slow in getting around to it. I say, 'You ought to have one, but it will put a terrible chill on the romance.' I mean, you know, maybe she'll move out!"

"All you really need to protect yourself is a written agreement saying there are no agreements," says Mark Goldman.

Though his firm is defending two businessmen clients against Marvin claims, as well as Marvin himself. "Most of our clients are worried but not willing to do anything about it," he says. "They're living wiith somebody and they don't exactly know how to bring it up."

Goldman, 36, is living with his ex-wife, with whom he had an agreement. "But the only reason I have it - otherwise I don't know how I would have gotten it - is I told her, "Look, honey,, I'm Lee Marvin's attorney! It would be very embarrassing for me not to have an agreement."