Les Blank's "Burden of Dreams" (at 10 tonight on Channel 26) is a castaway addition to that contemporary sub-genre of documentaries devoted to behind-the-scenes impressions of movies in production. The subject is a notorious problem production, "Fitzcarraldo," an allegorical adventure about a 19th-century entrepreneur's obsession with building an opera house in the Peruvian wilderness. German director Werner Herzog has been struggling to complete the film for the past few years on primitive locations along the shores of the Amazon.

It's possible that "Fitzcarraldo" may end its tortured journey at a few art-houses before the year is out, but then again it may not. At best "Burden of Dreams" offers a superficial, inconclusive impression of an esoteric project whose distribution is bound to be haphazard.

An admirable documentary specialist who works out of Oakland, Calif., Blank usually takes a contemplative view of regional American folkways.

"Burden" seems one of the least distinctive and satisfying commissions Blank has ever accepted. (The backers included the Usual High-Minded Suspects, from the Independent Documentary Fund to the National Endowment for the Arts.) One can appreciate the difficulty of drawing a bead on a subject as amorphous as a possibly sinking movie-in-progress. Evidently, Blank didn't even arrive near the scene of arduous perplexity until "Fitzcarraldo" had gone through its initial shipwreck: Herzog had to start all over again after Jason Robards, originally cast in the title role, contracted amoebic dysentery in the jungle, flew back to Connecticut and announced, under doctor's orders, that he had no intention of returning to Peru.

It's obvious that Blank has been forced into many organizational shortcuts in an effort to stitch the random footage together. The most annoying are post-dubbed snatches of chatter that feebly pretend to reproduce and even translate remarks that couldn't be recorded live. Even when the commentary is live and authentic, it may not bring this arbitrary document into focus. Herzog himself is a many-splendored source of contradictory testimony and self-conscious artistic bombast. When the end credits announce that a transcript of "Burden of Dreams" is available for $2, you may jump at the offer in order to savor nifties like "Everyday life is an illusion behind which lies the reality of dreams."

Nonsense this exquisite may suggest that something did snap while Herzog was shooting "Fitzcarraldo." However, "Burden of Dreams" indicates that Blank was never in a position to document Herzog's vicissitudes in a coherent way. Even when Blank is apparently on the scene during shooting mishaps linked to unwieldy props--a steamboat that has to be pulled up a steep incline and a second vessel that gets banged around on the river--his reconstruction seems to obscure or defuse the sense of crisis that existed at the time.