A tremendously flawed and beautifully photographed documentary about Central America, "Guatemala: When the Mountains Tremble," finally arrives on public television tonight after months of delay and bureaucratic fumbling. The film will be shown at 9 on Channels 26 and 32 and followed by a PBS-mandated half-hour panel discussion designed to raise political points the film ignores.

Bette Craig, a spokesman for Skylight Pictures, which made the film, says PBS twice announced air dates for the film and then scrubbed them after deciding the taped "wraparounds" (introductory material) made by the producers were unacceptable. Finally, the task of producing the wraparounds was given to Washington's WETA, which came up with the version to be seen at the conclusion of the film tonight. Journalist Charles Krause is the moderator.

The film is bluntly didactic and one-sided in portraying Guatemalan rebels as noble freedom fighters and Guatemalan peasants opposed to the present regime as the victims of repression, torture and squalor. Codirectors Thomas Sigel and Pamela Yates take a sledgehammer to their own credibility early in the film by including two scenes labeled "Historic Dramatization" and purporting to show the origins of a misguided U.S. policy toward the country. An actor playing the U.S. ambassador tells an actor playing the Guatemalan president, "You clean those Reds out of your government" and suggests that the United Fruit Co. not be deterred in its systematic exploitation of workers.

That isn't the end of the slant. The film is narrated by a peasant woman who seems to be reciting lines from a suspiciously eloquent script. Actors' voices are used as interpreters, and while the voices assigned to the guerrillas and their sympathizers are warm and earnest, those given the colonels and others in authority are slightly to the right of Bill Sikes in "Oliver Twist." Codirector Yates, in the post-mortem discussion, concedes that the heavily dramatized voices were a "mistake."

In spite of these shortcomings, the film is frequently impressive for the excellence of its photography, much of it affording a rare look at a Guatemala all but ignored by, or inaccessible to, the news departments of the commercial networks. And there is the occasional powerful note, most particularly the aftermath of a massacre, allegedly by the military, in a small village. The camera lingers on the bloodied bodies and then on the mourners, chiefly weeping women. One gets a dishearteningly vivid impression from this of poverty, grief and hopelessness.

Gail Christian, director of news and public affairs programming for the Public Broadcasting Service, conceded yesterday that PBS had been slightly clumsy in handling the project. It demanded that Skylight Pictures produce the wraparound segments, then rejected two versions of them, one featuring actress Susan Sarandon, the other with journalist Alexander Cockburn. Christian said it was felt that the wraparounds produced by Skylight failed "to say something the film didn't say" and instead were merely extensions of the movie.

But she denied the producers' charge that PBS was out to sabotage the film. "If we were out to get the show, all we had to say to them is 'Thank you, but no thank you' and reject it outright," Christian said. "We really took some heat on this film, and the producers are not as appreciative as they should be." Christian characterized the documentary as "a lovely film" and said the producers did "a great job," but she also said she thought the film was "real nice and real heavy-handed."

Christian was asked if there is now a more nervous political climate in public broadcasting, the result of Reagan administration pressures and the conservative political views of Reagan appointee Sonia Landau, chairman of the Corporation for Public Broadcasting (CPB). Christian said, "I don't think there's a 'more nervous political climate.' I just think that what we need to do is come up with some conclusion about how to handle these point-of-view films. The stations want shows that are closer to what you get from the networks in terms of documentaries; they want that balance."

One would hope that public television would be an arena where strong points of view from all sides could be expressed. On the other hand, giving air time to independent producers can lead to all kinds of problems when their programs have a high advocacy profile. The way PBS handled this particular case may have been sloppy, but the fact is, the film is getting onto the air, on many if not all PBS stations, and thus will be available to a wide national audience. Wider, perhaps, than the producers deserve.