It's only natural, in a picture-conscious society like ours, that investigative journalism should take the form of the documentary film.

It is not an easy road, film production and distribution being what they are, a world of big money, big theater chains and people not the least interested in rocking boats.

Nevertheless, the films get made, and they get seen. Two first-rate examples will be screened tonight at 7 and 9:15 at the Biograph Theater. They are "Song of the Canary" and "With Babies and Banners."

The canary in question is the little bird that coal miners used to take down the shaft with them to warn, by collapsing and dying, that carbon monoxide was present.

Today, workers themselves have become the canaries, the film asserts, with over 100,000 Americans dying every year of industrial diseases.

David Davis and Josh Hanig took their camera into a California chemical plant, discovered that workers were becoming sterile from being around a pesticide called DBCP. At first there are just accusations and denials, but finally some men are tested -- incredibly, no one had thought of this before -- and found sterile.

In a second episode, dust-caused brown lung is investigated in a Carolina factory, and we meet a remarkable group of fighting-mad retired people, the Carolina Brown Lung Association, which presses its case in a Senate hearing.

The second picture, by Washington filmmaker Lorraine Gray, tells how women helped the workers in the 1937 General Motors sit-down strike at Flint, Mich. Here too, the movie retelling blends into an actual event as the women attend the 40th reunion of the victory, wearing their red berets, find themselves excluded from the platform, and take action.

The filmers went to great lengths not to become part of the event themselves. They even sent their sound-woman home. But when the veteran strikers took to the platform with a passionate speech by Women's Emergency Brigade leader Genora Dollinger (". . . We are the foremothers of today's young women and we are proud of it . . ."), the camera was there to report it.

Putting together an independent documentary takes an amazing amount of energy. For one thing, the cost runs about $1,500 per minute of finished film.

Davis said he and Hanig worked with a $70,000 public television grant, a Film Fund grant and many small ones. He spent $100,000, wound up with 85 minutes of 16-mm color film. Gray and co-producers Lyn Goldfarb and Anne Bohlen needed slightly less for their 45-minute effort, got the usual small grants plus $17,500 from the National Endowment for the Arts but wound up $30,000 in debt.

The real problem, however, is distribution. Movie theaters are allergic to picture less than an hour long, whatever their politics. Television is forever cautious: Davis had a long battle with the Corporation for Public Broadcasting, which felt parts of his film were unfair to industry, but they compromised by having local stations add a studio discussion of the issue. The first screening may be held this fall.

Foreign TV gobbled up with pictures, gave them great play all over Europe. Film festivals brought in rentals, sales and prizes -- "Babies" won an Oscar nomination in '79.

But what the independent film-makers want most of all is that showing in the local movie theater. It can be done. A young man named Jerry Bruck pioneered self-distribution in 1974. A Johnny Appleseed of film, he traveled up and down the country, sleeping in people's living rooms, carrying his film on I.F. Stone literally on his back and a marquee banner in his suitcase.

"Bruck showed it was possible," Davis said. "Now there's a distribution cooperative, New Day Films, that handles a lot of independent pictures, puts out a catalogue and all."

The investigative documentary, or anyway the documentary with a point of view, seems to have begun with Emile De Antonio's "Point of Order" in 1964, a study of the McCarthy hearings. Since then the form has been expanding to cover a broad range of subjects.

A few, notably "Harlan Country U.S.A.," have made the big time, and feature-length pictures like "Northern Lights" seem to go over well at least as regional attractions: theater managers from the Dakotas and other northern states seek out the filmmakers for rentals.

But for the most part, if you hope to see fine, angry films like "Hearts and Minds," "Union Maids," "Six Days in Soweto" or "Fidel," you have to be lucky enough to live within driving distance of a theater that cares. That's what bucking the establishment if all about.