Eight years after they broke up, actor Lee Marvin and his former live-in companion, Michelle Triola Marvin, faced each other yesterday in a landmark breach-of-contract trial which may have far-reaching implications for unmarried couples who live together.

In a suprise opening move yesterday, the attorney for Michelle Marvin agreed to waive a jury trial and allow Los Angeles Superior Court Judge Arthur K. Marshall to decide the case. Testimony will begin Thursday and is expected to run for three or four weeks.

Michelle Marvin, 44, who legally took the actor's name although they never were married, is suing for what a wife would get in a divorce -- half the property accumulated by Marvin during the six years they lived together, after meeting on the set of the movie "Ship of Fools" in 1964. She is asking for approximately $1 million, including $100,000 for damages to her career as a nightclub singer.

Although the case has no formal legal significance outside California, attorneys say that it already has sparked hundreds of similar cases in more than a dozen states, including several multimillion-dollar Hollywood celebrity suits and at least two claims by homesexuals against their partners.

Michelle Marvin's attorney, the flamboyant Marvin Mitchelson, said that he agreed to waive the jury "because the judge in this case can deal with the complex legal issues more readily than a jury."

As testimony unfolds, Judge Marshall will be asked to examine the former couple's domestic past in order to determine whether, in the words of a 1976 California Supreme Court Decision (now known as the "Marvin Decision"), there was "an implied contract" to share property based on their "demonstrated conduct."

Mitchelson said during trial preliminaries that he plans to introduce as evidence "their joint bank accounts, paid bills in the name of Mrs. Lee Marvin, introductions of my client as Mrs. Lee Marvin to a Catholic bishop and to the premier of Japan, and even love letters."

Should the judge find merit in Michelle Marvin's claim and award her the settlement she asks, the second phase of the trial will deal with Marvin's sauce-for-the-gander cross-complaint asking $1 million in compensation for his services to her -- driving the car, escorting her to various entertainments, introducing her to important people like the premier of Japan.

The actor's attorneys -- a battery of five from the show-business specialist firm of Goldman and Kagon -- have declined to discuss defense strategies specifically. One of the attorneys outlined possible defenses "in cases of this type." Mark Goldman said last summer that, "the first defense is that he didn't promise her anything. The second defense is, even if he did promise, her services were defective, just like you can defend against a plumber if they were lousy services.

"The man has a right to defend and say, 'the housekeeping was miserable. Even if I did hire you as a companion, I really thought I was going to get more out of this than I did. You embarrassed me in front of my friends... didn't fulfill my needs and I had to get companionship elsewhere.'"

More recently, Goldman said that such testimony could get down to "each and every time she had a headache."

If so, the other side hints that they'll counter with testimony about the actor's "hard living and hard drinking."

"It could get messy," admitted Michelle Marvin as she sat chain-smoking in an empty corridor during trial preliminaries last week.

It already has. This week nine of her love letters from Lee Marvin were excerpted in an Associated Press story. "Oh, baby, I want so much for you, please," Marvin was quoted as having written.

When pressed, Michelle Marvin's attorney did not deny that he had provided the letters to AP. An attorney for the actor characterized the letter look as "a subtle way of letting someone know that if they are going to go through the course of this trial, their private life will be exposed to the public and they will be made miserable."

As he sat, also chain-smoking, in another empty corridor during the preliminaries, Lee Marvin seemed miserable indeed, much older than his 54 years. Accompanied by his current wife, Pamela Freeley, the childhood sweetheart he married shortly after breaking up with Michelle Marvin, the actor wore an untailored gray suit with baggy pants, his tie and collar askew.

When the trial's principals arrived at L.A. Superior Court last week to await assignment of a judge and a courtroom, the scene was pure Hollywood: a movie, Joseph Wambaugh's "The Onion Field," was being filmed in an adjacent courtroom and the hallway was filled with actors, extras and film crew. Attorney Mitchelson promptly agreed to a small press conference with local TV reporters.

Dressed like the well-to-do Hollywood housewife she claims she was for six years, Michelle Marvin nervously answered questions not related to specific evidence in the case. Between camera takes she complained of a dry mouth, prompting Mitchelson to crack, "Better your mouth than your eyes." The attorney quickly explained that his client was prone to tears when asked to recall her relationship with the actor.

"It hasn't been easy," Michelle Marvin said of her struggle to rebuild her life after the breakup. "Women today aren't greeted with smiles, as they should be."

Perhaps because she claims she "was like a wife to Lee Marvin" and gave up her career to "serve his needs," feminist groups have not rushed to her side with offers of financial or rhetorical support.

In pretrial motions, Lee Marvin's attorneys moved that the liability and financial portions of the trial be separated, meaning that the court should first determine whether Michelle Marvin was entitled to a settlement before scrutinizing the actor's personal worth.

Yesterday, Judge Marshall partially denied that motion by ruling that Mitchelson could present evidence of the actor's assets up until the time of the couple's break-up in May of 1970.Then, if liability is determined, the court may "trace" what became of those assets subsequently.

Now that the jury has been eliminated, a motion by Lee Marvin's attorneys to exclude such evidence as love letters becomes "immaterial," Goldman said.

"In a way, this has probably made the trial more interesting," he said, "because there was a chance that the public would never have had a chance to witness some of that stuff. Now we don't care if it's introduced, because a judge has the ability to ascertain its relevance."

Mitchelson says the letters are "essential" to his case, because "he (Marvin) takes the position in a deposition that he never really loved her, that it was a skin-deep relationship. But those letters show either that he Ioved her very much or that he lied to her."

Between May 1970 and November 1971, Michelle Marvin accepted monthly payments of $1,055 from Lee Marvin. Both Michelle Marvin and her attorney have said that the actor promised to make the payments for five years.

Goldman does not dispute the five-year time period, but he said, "Keep it in mind that it is our contention that there was no agreement. They were gratuitous payments and nothing more. In any event, it is not material in this lawsuit because that is not the agreement that Mitchelson is suing on."

When the trial resumes on Thursday, Mitchelson himself may emerge as the central character in the drama. The garrulous attorney has repeatedly declared, "I'm going to put marriage on trial in the Marvin case. I intend to show that when two people live together they have precisely and identically the same lifestyle as two people who have a license in their drawer and they should be treated as one and the same."

In explaining his goal to nationalize the Marvin decision, Mitchelson said, "I'm after a uniform marriage and cohabitation act. And I am convinced that, in the next five years, I or someone else will take a case like this to the U.S. Supreme Court."

Based in Los Angeles, Mitchelson is licensed to practice in 10 states and four foreign countries. Standing to collect one third of any settlement to Michelle Marvin, he also represents model Cindy Lang and Karen Ecklund in their multimillion-dollar companionship claims against rock singer Alice Cooper and actor Nick Nolte respectively.

Other California cases have included a claim by actress Britt Eklund against rock star Rod Stewart, and the more recent claim by a man alleging he was the companion of the late actor James Daly. In San Diego, a judge awarded a lesbian partner temporary support, citing the Marvin decision as a precedent.

The decision also has been formally recognized by courts in Minnesota, Oregon, Washington, Wisconsin and Michigan. However, a Georgia court has rejected a claim based on the decision.