The term "silent film" is a convenient but slippery catchphrase to describe movies that were made in the years before Warner Bros. introduced spoken dialogue in the late 1920s. In fact, early films were rarely silent, but accompanied by music of considerable sophistication, played on the piano or organ or by full orchestra. No less distinguished a musician than Camille Saint-Saens wrote for the "silent" film; so did composers Arthur Honegger, Darius Milhaud and Dmitri Shostakovich.

The two short documentaries by the late poet, critic and filmmaker Pare Lorentz -- "The Plow That Broke the Plains" (1936) and "The River" (1938) -- which the American Film Institute will present today and tomorrow at its AFI Silver Theatre and Cultural Center in Silver Spring, are not technically silent films, as both feature narration and some sound effects, dubbed in after the fact. And yet their idiosyncratic twinning of music and image, combined with their lack of dialogue, infuses them with the spirit of both the silent film and the spectacular, plotless avant-garde syntheses that composer Philip Glass and filmmaker Godfrey Reggio would explore in works such as "Koyaanisqatsi" (1983) and "Powaqqatsi" (1988) half a century later.

It was Lorentz's decision to collaborate with the American composer Virgil Thomson (1896-1989) that elevated these films from visually arresting but decidedly of-its-time documentary realism into the realm of totemic American art. Thomson took Lorentz's images and set them to music that was both accessible and sophisticated, combining cowboy songs, bugle calls, Baptist hymns, hints of jazz and tangy dissonance, and then setting them all for saxophone, banjo, harmonium and orchestra. For these AFI performances, Thomson's scores will be performed live by a 40-piece orchestra, the Post-Classical Ensemble, under the musical direction of Angel Gil-Ordonez, and the narration will be read by local actor Floyd King. Immediately after the showings, there will be an onstage discussion of the Lorentz-Thomson partnership, featuring Andy Trudeau from National Public Radio, composer Charles Fussell, filmmaker George Stoney and Post-Classical Ensemble Artistic Director Joseph Horowitz.

It was the U.S. government itself that sponsored these two films -- $6,000 from the Department of Agriculture for "The Plow That Broke the Plains" and, after "Plow" had been released and admired, a full $50,000 for "The River" (the latter sum raised by undersecretary Rexford Tugwell in a half-hour, through a phone call to President Franklin D. Roosevelt).

To call "The Plow That Broke the Plains" and "The River" propaganda is to belabor the obvious. Both were lyrical exaltations of the New Deal, paid for by the New Deal -- the first a plea for desperate farmers and their families in the Great Plains, the latter a history of the Mississippi River culminating in the creation of the Tennessee Valley Authority. They serve an agenda and serve it well but will seem to many rather starry-eyed and promotional to count as successful history (although the Baltimore Sun said "Plow" included "more serious drama in this truthful record of the soil than in all the 'Covered Wagons' and 'Big Trails' produced by the commercial cinema").

Judged on their artistic merits, the films make a far stronger impression. Thomson's music is wonderfully fluid and expressive, and the images Lorentz presents -- whether the Mississippi roaring along from Minnesota to New Orleans or miles upon miles of parched desert grasses -- are hauntingly evocative. (How strange to see a paddle-wheel riverboat as a form of serious transportation, rather than a day-tripper's excuse for some gambling and beer.) The texts, by Lorentz himself, combine Gertrude Stein-ian reiteration with exuberant list-making in the manner of Walt Whitman (although one of these, which refers, in stentorian fashion, to "the Wachita, the Wichita, the Red and the Yazoo" rivers sounds more like a declamation from Groucho Marx).

Thomson has left a detailed description of the working method he evolved with Lorentz. "I played to Pare on the piano all the material that I planned to use and got his acceptance of it before composing with it," he told Robert L. Snyder, who was then a professor at Kansas State University, in 1961. "After Pare had cut his film, I composed my musical sections in accordance with his timing and played them for him on the piano in front of a projection of the film. After acceptance by him in this form, I orchestrated the complete music and it was recorded.

"At this point arrived the event which Pare had been working toward and waiting for all the time. He likes to cut his film to an existing musical background. But since a background cannot be composed, orchestrated and recorded until the film has been cut and the lengths of the shots and sequences fixed, Pare has to go through a cutting for the visual narrative, but his heart is not fully in it. When he gets the final recorded music track, then he goes back to the cutting room, finds inspiration for expressive visual narration through the musical detail, and wholly recuts his film."

In short, the film fed the music and the music fed the film -- a true collaboration.

Lorentz went on to make several more films, but none was as powerful and influential as these first ventures. Upon Lorentz's death in March 1992, the radical historian Patrick Renshaw, writing in the London newspaper the Independent, noted that "no other filmmaker has been able to secure such a high international reputation as Pare Lorentz did on the strength of just two films.

"Since first seeing them 40 years ago at the Walthamstow Film Society I have been haunted by their images of the devastation caused by natural calamities, and the heroic efforts made during the New Deal to provide answers," Renshaw continued. "Generations of my students watch them enthralled. Other feature films -- John Ford's version of Steinbeck's novel 'The Grapes of Wrath,' or Elia Kazan's 'Wild River' -- help us to understand the same issues. But neither does so with such imagination and economy."

As for Thomson, he went on to compose for another half-century, while distinguishing himself as perhaps America's wittiest and most perceptive homegrown music critic during his tenure at the New York Herald Tribune from 1940 to 1954. In 1948, for the first and only time in the history of the Pulitzer Prize, the composition award went to a film score -- Robert J. Flaherty's "Louisiana Story," with music by Virgil Thomson.

The Plow That Broke the Plains and The River will be presented by the Post-Classical Ensemble today and tomorrow at 3 p.m. at the AFI Silver Theatre and Cultural Center, 8633 Colesville Road, Silver Spring. Call 301-495-6720 or visit Tickets are $25 and available online.

"The River" is a tale of the Mississippi that ends with the birth of the Tennessee Valley Authority.Pare Lorentz, above, tapped the talents of composer Virgil Thomson for his two films.