Eva Marie Saint has been married for 30 years, but cannot for the life of her explain why. "We do everything together," she volunteered.

Then she went on a bit, trying other theories, such as, "I'd already done 'On the Waterfront' when we got married, so I already had my profession. And we both wanted to have a family." Taking another tack, she tried: "He's a director. I would never even date actors, you know, because they have needs that aren't reflected in the other person."

"In fact, our wedding anniversary is tomorrow," she said at lunch Monday, passing further explanation to Jeffrey Hayden, three decades' worth of husband seated across the parsley scallops at Jean Louis. Hayden is a veteran television director, and has worked on "The Incredible Hulk" and ABC's "Afternoon Specials," which is more or less the gamut of series life in Los Angeles.

A nine-second pause ensued (timed by Accutron wristwatch). Then: "No, Eva -- it's October 29."

Science has not yet figured out what makes marriages last in Los Angeles. In fact, science is not even working on it. However, a husband who remembers anniversaries is his own explanation.

It could easily be said that there was some reason for this lunch and this question (viz., "To what would you attribute the longevity of your marriage?"). It could be said that Eva Marie Saint was in Monday night's remake of "Splendor in the Grass" on NBC. Or it could be pointed out that she was here Sunday for the Richard L. Coe awards, and performed the part of Blanche in Tennessee Williams' "A Streetcar Named Desire" in a fund-raising excerpt.

Or it could be said that the world needed to ask her again what it was like to be chased by Cary Grant across Mount Rushmore in Hitchcock's "North by Northwest." Or, "What was the young Marlon Brando really like?" which in fact she did get asked, between the scallops and the lamb.

But the real reason for this report is that you would be crazy not to have lunch with Eva Marie Saint and Jeffrey Hayden if you had the chance.

Thus reason is caught short, and undone, and you might as well just dine as well as possible and not worry about it. A Lovely Couple

Gosh, frankly, what a lovely couple. Hayden is a sort of enthusiastic but thoughtful man with stylish eyeglasses and a necktie on a plaid shirt; and Saint is slim and lovely and touches your arm when making a point, and after about an hour you can get away with calling her "Eva." You could try it in 45 minutes, but it would be wrong.

On the way to Washington, they stopped in New York to see "Nicholas Nickleby," the 8 1/2-hour play based on Dickens' novel. They were flabbergasted by the skill and enthusiasm of the Royal Shakespeare Company -- and mind you, this is the 2 p.m. matinee which concluded after 11 p.m., and they had arrived the night before on a coast-to-coast flight that had been delayed on the runway at Los Angeles for four hours.

"I'm a little shy, but Jeff always says if you like the performances go backstage and say so. So we went and introduced ourselves to Roger Rees, who plays Nicholas, and he opened a bottle of wine and we became friends right away. Actors can do that."

Yes, but 30 years of marriage?

"We play tennis together," she volunteered.

Hayden said, "I used to have a stock response, you know, when on television. I'd say, 'Well, it's because we have an active sex life.' As soon as I said that, the interviewer would always go blip right back to Eva and say something like, 'Um, what was Brando really like?' Used to scare them a little."

Saint giggled demurely.

"Then I heard of a study which actually concluded that an active sex life led to long marriages, so I had to stop saying it," Hayden said. "Too serious."

They have two children. Laurette, just out of Stanford, is working with the legendary filmmaker Roger Corman. She's 23. Son Darrell, 26, is employed with the graphic designer Saul Bass.

Eva Marie Saint first realized she was pregnant with Darrell on a small boat en route from Block Island to New Rochelle. The sea was making up some, and she became nervous and asked Jeffrey to turn back. He did, without a complaint or accusation (Oh weakness, thou art woman!) or any of that stuff. Turned out the lady was going to have a baby.

"A lot of being married a long time is luck," she said, looking at Hayden. "I mean, getting a good one." The Real Brando

The real Marlon Brando didn't come up until later. Instead, the conversation turned to television today, and why it isn't better.

"I loved the first three hours of 'How the West Was Won,' because I'd wanted to do a western and never did. I liked my part because it was that of a strong, pioneer woman. She did more than make dumplings and do the wash. Jim Burns, who was writing it, promised it'd be that way. But then, as always happens on series, Jim wasn't writing them anymore after three scripts. Suddenly it was awful, and I started walking off the set and things like that. I went to ABC and they let me out of the contract. I've never wanted to do a series since."

Hayden was rolling his eyes. He has been in television for 25 years, and is not greatly encouraged.

"Oh, the system we have seems to be designed to allow only for the most aggressive, salesman types to rise to the top. The scripts are terrible because everybody's rising, nobody's writing. The writer wants to be a story editor. The story editor wants to be a producer. The producer wants to be a line producer. The line producer wants to be an executive producer. And the executive producer want to do spinoffs. Nobody has time to say, 'Give me a script with a beginning, middle and end that contains a certain amount of human conflict.' Instead, you get car chases." As a director, Hayden says he has been unsuccessful in trying to argue car chases out of scripts.

The problem is probably not immediately solvable. "What has done this is the need to get to the next commercial without losing people. Used to be 12 minutes, now it's eight or nine. You can't slow down for human conflict."

Hayden says years of directing series TV has made him suspicious of his own reactions. He didn't like the three-hour-long movie "The French Lieutenant's Woman" much, "but I kept wondering -- is it because I'm really waiting for a commercial? Has the business done that to me?" He concluded, in the end, that it was just a bad movie.

Saint said she admires Meryl Streep, and hopes she can survive the "hype." "It's very hard to live up to those kind of expectations," she said."Being on the cover of Time and all the rest."

But she survived, didn't she? "On the Waterfront" was, after all, her first picture, and made her a star.

"Yes, I was on the cover of Life. But you know, it wasn't as intense in those days. I remember Time magazine called me and said they wanted to do an interview, but I said no -- I couldn't, Jeff and I had a trip planned in our little boat. We were going to go from Block Island to Montauk. I had already been in Life. Of course, Time never called back." The Brando Mystique

After "On the Waterfront," she is most often asked about "North by Northwest." Sometimes, however, people forget to ask her, and if so, she doesn't always bring it up. But she has said (in the past) that when Hitchcock picked her for the part of the beautiful spy he said that "I was sexy, dangerous, mysterious and alluring," and that although her husband had been telling her that for years, when Hitchcock told her she believed it. She has also said that the famous Mount Rushmore scene was filmed on a lot at Metro and that the mountain, made of rubber, was 60 feet high. One day, climbing on Lincoln's nose, she saw the mattresses laid out way down there, in case she should fall, and got quite scared.

As for Brando, the fact is she was pretty impressed. "He was very handsome. I had gotten the movie role because they'd seen me in my first Broadway play, 'Trip to Bountiful,' with Lillian Gish. So during the day I took the tubes over to Hoboken and shot the movie, rehearsing between takes. Then I took the tubes home in the afternoon and cooked Jeff his dinner. Then at night I did the play on Broadway. It was quite an interesting time for a young actress."

But Brando, what was he like?

"I was very attracted to him. I used to tell Jeff, it's a good thing you married me, because Marlon is quite attractive."

Oops. All conversation suddenly stopped. Maybe, somebody had speculated innocently, it was bad luck to talk about a good marriage. Maybe it should be observed with awe and silence, like a white-knuckle no-hitter.

No, he said, he didn't think so.

Neither did she.