ONCE MIGHT BE happenstance, twice coincidence, but the third time, the third time it's for sure.

Once for director Joan Micklin Silver was "Hester Street," a low-budget, Yiddish language surprise that charmed audiences from Anchorage to Biloxi and ended up earning more than 10 times its production cost.

Twice was "Bernice Bobs Her Hair," starring Shelley Duvall and based on the F. Scott Fitzgerald short story, a major critical and popular success on PBS.

And if advance indications mean anything at all, the third time will be "Between The Lines," an extraordinarily warm and pleasing comedy about life on a Boston alternative newspaper. Set to open this week in New York and on May 18 at the Avalon, "Between The Lines" sold out two shows at the American Film Institute and was such a sensation at the U.S.A. Film Festival in Dallas that the director says "We wanted to stay and show the film there forever, and you know that's not because we want to live in Dallas."

If Joan Micklin Silver's life was a Hollywood movie, that's exactly where, as a bona fide. Hot Director, she'd be headed next, ready to tackle The Big Picture. Yet paradoxically her next film project will see her not directing but producing a prison drama. "On The Yard," to be directed by her husband, Ray, the man who produced "Hester Street" and "Between The Lines" for their own company, Midwest Film Productions. If that sounds very cozy, it's supposed to.

"I always felt we do these films together, it's very hard to make movies and its nice to have that kind of support," Joan Silver says. "Lots of times the director-producer relationship gets to be a battle of egos. We don't have to go through all that silly stuff."

But it's more than marital fidelity that has attached Joan Silver to Midwest Film. For her very success is a function of that company's uniqueness, of it's being what she calls "a mini-mini studio," capable not only of producing films but of distributing them to theaters, and distributing them very well, thank you.

It is this capacity that causes Joan Silver to say "I'm one of the most fortunate people in America. If we want to do a project, we can do it. When a major studio executive called me from Hollywood just to say how much he disliked the 'Between The Lines' script, I was able to tell him we were going right into production with it. It's the best feeling in the world."

Midwest Film was not always an organization working toward what Ray Silver calls "total fimmaking capacity." That idea began when the major studios, one by one, stoutly refused to send "Hester Street" out into the world.

"I'd been 20 years on my own in real estate," Ray Silver says," and the only reason that was possible was that I was able to control the decisions being made. When we were unable to find distribution for 'Hester Street,' that all came back to me in a rush. Unless you control the destiny of your film, you're at the mercy of a system which by everyone's admission, even those who are running it, is not working very well.

And though they laugh at Variety's description of them "flogging 'Hester Street' into a $5,000,000 grosser" - "our poor little film, never," Joan says, mock tearful - in fact it was very largely just persnickety hard work combined with a shortage of good Hollywood product that got "Hester Street," and probably will get "Between The Lines" as well, into wide national distribution.

"Most theaters are booked a year ahead with the studio product line - the majors tell them 'Film A will be a blockbuster, you'll get 10 weeks, Film B will give you six weeks,' and so on," Ray Silver explains. "Then what happens is that the pictures begin to fall out of bed, huge holes inevitably open up. So the studios say 'That's all right, we'll give a double bill of rereleases.' Our job was to convince the exhibitors that our film would do more business than those retreads," a job that entailed "hours and hours on the phone," as well as long, tiring personal visits to the hinterlands.

Yet their big success with "Hester Street" notwithstanding, the Silvers found that when they tried interesting the majors in first the script of "Between The Lines" and then the finished product, they couldn't get a commitment. It wasn't that the studio biggies thought the film was bad, it was stranger than that: like James Dean in everything he played, the Silvers' film was a misfit, it just wouldn't adapt to accepted patterns. So they ended up using the profits of "Hester Street" and making it themselves.

"Studio merchandizing is geared toward broad, national consensus films, films with bust-out potential," Ray Silver says. "If a film can't be marketed in conventional, established patterns, it doesn't matter who you are, they won't take the film on.

"Look at 'Taxi Driver.' Robert De Niro and Martin Scorcese had to work for practically nothing just to get it made, and still it played only 18 cities because the studios didn't know how to market it nationally, while 'Hester Street' had 900 play dates. With 'Between The Lines' the studios asked us 'Where are the handles?' They said they didn't know what to do with a film like this, a film that didn't fall into an easily pegged category."

Given all this, it's not surprising that Joan Silver has "that sort of wary feeling" about eventually working Hollywood. "I'm not exactly lionized now, California isn't calling hourly," she says, but even if that does happen she feels secure in her bearings. "I'm 41 years old, it's not as though I'm 21. The things that are important to me will be important no matter what happens. It's sort of like lotuslands. If it happens, it happens."

Yes, she is excited about the possibility of using actors and budgets that have previously been beyond her means, but she is also afraid of losing her current control and plainly horrified by the new movie trend "toward giganticism, toward big zap movies that just go out and throttle you. After seeing a few of them I had a terrible desire to run home and kind of spread my wings over my own film."

Ultimately, more than the business savy of her company, it is the uniqueness of those films that has made Joan Micklin Silver special as a director. Which is just as it should be.

"Many film people seem superdecadent, into the undersides of human nature, which means that audiences are often starved for a feeling of humanity," she says, admitting that if forced to pick an absolute favorite director or "we'll cut your head off," she would chose (who else but) Francois Truffaut.

"And it's not as though I sit down with my own films and say 'I want to get human warmth into this.' A lot of what happens in film is an outgrowth of your personality. So many directors have that cynical and alienated quality, the idea that everyone's a rotter. I just don't happento feel that way."