*** NEIL YOUNG, “Unplugged”; <i> Reprise</i> : *** ROD STEWART, “Unplugged . . . And Seated”; <i> Warner Bros.</i> : *** VARIOUS ARTISTS, “Uptown Unplugged”; <i> Uptown/MCA</i>

What was once a hip, informal TV hootenanny has inevitably turned into a cheesy cottage industry--”MTV Unplugged,” that is, the formerly modest acoustic show that’s now a bandwagon for superstars to jump onto and make product out of. Its trendiness can’t help but inspire cynicism; then again, most of the episodes are nice.

Young’s “Unplugged” is a superior document of his last road trip, with no sense of being a TV soundtrack or a nostalgia fest. The first half, with Young solo on guitar or piano, is all spooky and dirge-like, culminating in his weird, funereal pump-organ version of “Like a Hurricane.” The second half, on which he’s joined by a quiet band, is equally mellow but warmer, following in the key of his “Harvest Moon” material.

Stewart’s approach isn’t nearly so stripped down, naturally. There’s a full band and orchestra, doing a fair amount of rocking out amid the ballads, and you wouldn’t even notice the absence of electric guitars or synths if you didn’t become aware at some point how unusually tasteful this all is for Stewart. This doesn’t seem so much like a pointedly “acoustic” detour as just close to the way Stewart would be smart to arrange his stuff all the time.

Much the same could be said for the Uptown Records roster. The black-music label’s collective “Unplugged” has its young artists backed more traditionally--but no less energetically--than usual by an R&B; band hotly dominated by piano, horns and rhythm section (the fat bass part of which, at least, sounds as if it was pretty near an AC outlet).

Young crooners Jodeci and Mary J. Blige strut their gospel-influenced stuff more effectively here than on their regular, overproduced releases, while rappers Heavy D. and Father M.C. prove that LL Cool J’s premier “Unplugged” rap episode wasn’t just a hip-hop fluke after all.

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