THIRD WORLD has never pretended to be strictly a reggae band. Unlike most mainstream reggae bands, which at best tacitly acknowledge their debt to soul and R&B, Third World has always been openly expressive about how black American pop has affected its Jamaican music-making.

Skim through "Reggae Greats: Third World," an anthology of their early hits, and you'll hear a wide variety of musical influences bubbling up through the heavy bass and skanking guitar. "Cool Meditation," with its warm harmonies and slick arrangement, owes much to the polished Philly soul of the O'Jays, while "African Woman" relies on vocal interplay and a monolithic groove reminiscent of Harold Melvin's Blue Notes.

True, there are a few songs that are simply straight reggae -- "96 Degrees in the Shade" is the standout -- but the best material is a true fusion, tying rich, soulful melodies like that behind "Now That We've Found Love" to a sturdy reggae beat.

Unfortunately, blending diverse styles is little appreciated on the American airwaves, so it ought to come as no surprise that Third World has moved even further from its reggae origins as its stake in the American charts has grown. In fact, "Sense of Purpose," the group's latest album, is mostly an R&B effort. Sure, there are moments like "One Song (Nyahbinghi)" that touch roots for the band, but it seems more inclined to hope that the tokenism of "Reggae Jam Boogie" will placate older fans while the slick pop reels in new ones. Not that change of pace is in anyway a cheat, for from the rap-fueled "Children of the World" to the uplifting dance pulse of the title song, Third World proves itself to be an ace R&B act with definite chart potential.

Dennis Brown has been making slick, generally vapid albums in this country for some years now, yet as his side of "Judge Not" demonstrates, he's capable of reverting to a righteous reggae sound. In fact, the three singles compiled here are among his best work in years, combining fervor and wit with the sort of aplomb rarely heard since the death of Bob Marley.

Brown's performance is so powerful that it almost completely overwhelms his B-side companion, Gregory Isaacs. Maybe it's that Isaacs' crooning delivery lacks the edge required for Brown's moral indignation. Certainly, Isaacs' warnings to a "Street Walker" seem more solicitous than stern.

But on his own album, "Reggae Greats: Gregory Isaacs Live," the singer manages -- even with the ragged backing he gets from the Roots Radics -- to charm his way through, coaxing and teasing his fans in the same sweet-voiced way he seduces the women in his songs. Like a true ladies' man, Isaacs understands that it's not what you say, but how you say it that counts.

THIRD WORLD -- "Sense of Purpose" (Columbia FC 39877) and "Reggae Greats: Third World" Mango MLTS 9789);

DENNIS BROWN & GREGORY ISAACS -- "Judge Not" (Greensleeves CGR/GREL 72);

GREGORY ISAACS -- "Reggae Greats: Gregory Isaacs Live" (Mango MLTS 9782); all appearing at the Reggae Sun Splash Saturday at the Washington Convention Center.