This romp through gospel music is a G-rated joy

Say Amen, Somebody is a romp through the world of gospel music - full of soulful tunes, earnest lyrics, and friendly visits with musicians who sing them to the rooftops. It's a G-rated joy. And it's a fine follow-up to the last movie by George A. Nierenberg, ''No Maps on My Taps,'' which took a somewhat more somber look at the hoofers who struggle to keep American tap-dancing alive.

Since I enjoyed ''Say Amen'' at last year's New York Film Festival, I was pleased to see it picked up for commercial release - a happy fate that doesn't greet many documentaries. But then, Nierenberg doesn't think of his films as ''documentaries'' per se.

In fact, some of his methods go directly against the grain of much nonfiction filmmaking. A soft-spoken radical, he shuns the doctrine that a director shouldn't influence (much less manipulate) what's being photographed. On the contrary, Nierenberg plunges into his projects with all the resources at his disposal, as willing to stage a scene - in a natural setting - as to catch one on the run.

He got the idea for a gospel-music film when a friend told him there had never been one. His curiosity piqued, he and his wife ''started going to churches, gospel programs, halls - anywhere we could find this music, which we knew nothing about,'' he told me recently at his office here. ''We got very involved, and liked it a lot. It seemed a subject I could really dig into.'' As for his ignorance, ''It was an advantage. I could approach the whole thing from a fresh point of view.''

The next step was finding personalities the film could focus on. ''For me,'' says Nierenberg, ''the first year of putting a film together is almost like casting it, just as you'd cast a fiction movie. My films are character-oriented, so I look for people who will come across well - people who can capture an audience simply with who they are.'' Among his finds were Thomas A. Dorsey, who has been called ''the father of gospel music,'' and noted performer Willie Mae Ford Smith, who appears with various members of her family.

''If I hadn't found the right people, I probably wouldn't have gone ahead with this subject,'' acknowledges Nierenberg, who enjoys getting involved with his ''characters'' as much as he relishes the technical challenges of shooting and editing. ''My goal,'' he continues, ''is to portray people who are really doing things, not just acting at it.''

To reach this goal, Nierenberg uses the film medium as fully as he can. ''I have to develop a relationship with my characters, and understand a certain essence of them. Pinpointing this requires a long editing process that begins even before the film is shot. I sort out possibilities in my head, choosing aspects of their lives that I want to re-create on film.''

He then proceeds carefully with this ''re-creation,'' controlling it as much as possible without distorting it. ''Everything that occurs on film is something I've already experienced,'' he says. ''My job is to make it happen again, for the camera.''

It doesn't bother him that most documentarians prefer filming events as they happen, spontaneously, for the first time.

''I don't believe in capturing the moment when it first occurs,'' he explains , ''because I know that moments aren't singular. They happen time and again. If someone has a conflict with his wife, or goes to help somebody, it's something that happens over and over. I like to see if it works - through my own eyes - before putting it on film.

''Then the actual shooting just rolls along. I shot this whole thing in 15 days, which isn't long for a 100-minute film with no studio controls! I could do that because I knew just what I was going after with my cameras. . . .''

It's a risky business, Nierenberg admits. ''When I finally do start shooting, after all the preparation,'' he says, ''I have a pretty good idea of what will happen in a situation I want to film. But it might not happen as well as before, or it might change in some way.''

Still, he prefers his method to the direct cinema veritem style. ''I tried that approach long ago,'' he says. ''I set rules for myself, and promised I wouldn't affect anything that went on, because if I did, there would be something 'wrong' with it. But it was stupid to put on blinders. The film was a mishmash. And I realized I could have made it so much better, so much clearer, by just reaching out and controlling things a bit!''

Hence his new attitude. ''I don't like sitting around and waiting for something to happen. I'd rather create a situation that will make it happen. Why limit myself? Why not open myself to all possibilities and all techniques? Just as long as it helps me express my subject matter the best way on film.''

Yet caution is needed when putting real-life ''characters'' in a planned situation, lest it interfere with their natural rhythms and habits.

''The context must be completely motivated,'' Nierenberg says, ''and the people must be there for its own sake, not to re-create a scene. My job is to make the feeling real for them, not just set them up to say certain things. If the environment isn't right, the characters will be uncomfortable. Then I'll have to change something, take a break, or give somebody a line to set things moving.

''But once somebody does respond, it doesn't matter whether the cameras are going or not. The response is always genuine - it has to be! - and the rest just snowballs.''

The objective is ''to be concerned about the truth. You're not trying to make the characters into people they're not; you're trying to be honest as to who they are. So whenever you try to re-create a situation, you have to assume a lot of responsibility. After all, you're dealing with somebody's life.''

To this day, Nierenberg himself is ''amazed at how natural people can be in front of the camera, even in a situation that's almost as controlled as a fiction film.'' But the combination of natural subjects and carefully devised structure is the crux of ''Say Amen,'' in his view. ''It reaches people because of its control,'' he says. ''And that matters a lot to me.

''I want to reach a broad audience. My subject matter may be educational, but I want to educate through entertaining. I have to get people involved with the characters and who they are, trusting and believing in them.

''One of my goals was to dispel the mystique of the gospel experience, which people have all kinds of misconceptions about, or don't know what to think of. I wanted to enter that experience through my characters - introducing my audience to them so there would be a lot of trust and liking. Then you'd see the experience through their eyes. If that happens, then I've gotten what I was after. . . .'' Multimedia evening

Patrons walking into Meredith Monk's next show will be greeted by a movie - starring a mermaid - to get them into the right mood.

And what is the right mood for a multimedia cabaret evening called Turtle Dreams? A mixture of whimsy and wonder, with an undercurrent of serious thought about where the world is headed. Those are some main ingredients of the latest Monk work, according to the talented artist who directed, composed, and choreographed it, and who will be the most prominent performer when it opens April 19 at New York's Plexus Club. It will run through May 1, to be followed by a theatrical run next fall, and its music - spectacular, judging from a cassette version I've heard - will be available this summer on an ECM/Warner Bros. record.

Miss Monk is no novice at blending film and live action into a seamless flow, having mixed various media in narrative and concert-type productions before. ''Turtle Dreams'' will alternate live music and movement - including ''a funny cha-cha where everyone sings, dances, and plays the organ'' - with movie sequences. The result, she says, will be ''futuristic'' and even ''apocalyptic, '' suggesting dark thoughts about the future of mankind but finally insisting on the redemptive power of ''humor and heart.''

Although the Monk style is strikingly different from any other on the current scene, in cinema as well as music and dance, it has been increasingly visible lately. Her gentle film-elegy on time and history, ''Ellis Island,'' was shown nationally on PBS in February, and her last onstage production - ''Specimen Days ,'' rooted in Civil War imagery - proved so popular with New York audiences that it was revived as soon as she returned from the international tour that curtailed its original run.

''Turtle Dreams'' marks another step in her evolution, meshing film with live performances in a deliberately informal setting that will ''break down the formal art atmosphere'' which sometimes seems to separate artists from their audiences. If it lives up to earlier Monk efforts, it could be a ''variety show'' to remember.