One of the more significant aspects of art in rock'n'roll is its adaptability to politics. Taking over from the folk music of the '50s and early '60s, rock music forged a new voice, whose volume and accesibility to large masses of people made it influential almost before anyone realized the potential.

It was clear in the '60s that many rock musicians were trying to say more through their work than "roll over, Beethoven," and they used many different musical styles to accomplish their goals. Besides the obivous social commentaries presented by people like Bob Dylan and Peter, Paul and Mary - performers who were holdovers from the folk days - bands like the Jefferson Airplane blasted out "Volunteers" and Crosby, Stills and Nash quietly expressed themselves through songs like "Long Time Gone" and "Wooden Ships." The times were indeed a-changin."

The '70s, though, brought a new type of sound and a new type of audience, and by the mid-'70s rock's importance as a harbinger of social and political change had been reduced to near zero. Rather than offend anyone, bands like Fleetwood Mac stuck to love laments, while wattage and macho do all their talking for them. The New Wave pumped some awareness back into the music, but New Wave groups' social observations were often undercut by their bizarre behavior.

So it's with a great deal of pleasure that one discovers a rock'n'roll band today that's truly a political entity without any compromise in its music or its presentation.

The Tom Robinson Band, which had been scheduled to appear at the Bayou this weekend but cancealed, is about as overtly political as a band can get without being didatic, yet its music is legitimate rock'n' roll.

The Tom Robinson Band was formed in 1977 and made news when bassist, composer, lead vocalist and leader Tome Robinson declared he was a homosexual. Not only did he say it, but he sang it before live audiences in "Glad to Be Gay." This is not exactly recommended procedure for stardom among young working-class Britons, who often beat such "misfits" to a pulp for entertainment. Yet Robinson, despite a few close calls, has not only survived but is gaining a substantial audience - both in England and in the United States.

One reason is that a new album, "TRB Two," is even better than his first one, "Power in the Darkness" (which was good), and another is that Robinson is no limp-wristed teaser who caters to an androgynous crowd. Tom Robinson is raw and dynamic. His voice nearly cracks from trying to jam more energy through his windpipe than it can handle. And his songs are first-rate.

"TRB Two" is more sophisticated than Robinson's debut album. A major factor in this is Todd Rundgren, who produced and mixed the album and added Utopia's Kasim Sulton to some of the tunes. Another plus is that though Robinson has kept guitarist Danny Kustow, he's replaced drummer "Dolphin" Taylor with Preston Heyman and keyboardist Mark Ambler with Ian "Quince" Parker - and both newcomers are superior musicians.

As for the songs, there's a lot of substance and very little rhetoic. "All Right All Night" is a straight-ahead rocker, while "Sorry Mr. Harris" shows Robinson's social savvy. As the melody bouces jauntily along, Robinson describes a rather frightening police interrogation. "Blue Murder" is equally unsparing in its depiction of crime, its aftermath, and how to avoid it. No gay-rights formula propaganda here. No cliches, either. Just straight talk.(It should be noted that there is little, if any direct reference to gay rights on "TRB Two." Also, "Glad to Be Gay" did not appear on the first Tom Robinson album, but did not show up here on a four-song sampler distributed by the record company and on a special "bonus LP" included in many copies of "Power in the Darkness9." That track is live. No studio version of "Glad to Be Gay" exists on either album).

Straight talk comes naturally to Robinson. As he said in England's New Musical Express: "I got no illusions about the political left any more than the right; just a shrewd idea which of the two side's gonna stomp on us first . . . To stand aside is to take sides. If music can cease even a tiny fraction of the prejudice and intolerance in this world, then it's worth trying. I don't call that unnecessary up for your rights."

Now that we've established politics as an integral aspect of rock'n'roll art, it should be pointed out that "fun" is just as integral a part of rock'n'roll in general. Van Halen is fun. No power-rock band, with the possible exceptions of Deep Purple and, currently, Bad Company and Foreigner, plays with more personality than Van Halen.

Its second album, "Van Halen II," is not as impressive as its debut, but it's worth it just to hear the menace underlying the Linda Ronstadt hit "You're No Good." Strangely enough, like Ronstadt, Van Halen made its name in the Los Angeles area, not a region known for its contribution to heavy metal.

Van Halen is heavy metal, but light-hearted metal. With bands like Styx, Yes, Supertramp and Kansas practcally choking on their own pretensions, it's nice to hear four guys who just like to play simple chord progressions real loud. No grimmicks, just fun. Exactly what some aspects of rock'n'roll are all about. CAPTION: Picture, VAN HALEN: THE FUN OF A POWER-ROCK BAND