1997, it might seem, was the year ska-punk finally infiltrated rock's mainstream. The year's biggest-selling rock group was No Doubt, the standard-bearer for Southern California's long-simmering ska-punk scene. Southern California's Goldfinger and Reel Big Fish and Boston's Mighty Mighty Bosstones also put ska-punk on the charts.

And yet the Jamaican rhythm that dominated modern-rock radio last year was heard in such songs as Sugar Ray's "Fly" and Sublime's "Wrong Way." It was reggae, not ska.

The distinction may seem arcane. Both ska and reggae evolved in Jamaica in the '60s, and both once seemed exotic to mainstream-rock listeners, but in recent years they have demonstrated their enduring influence on Anglo-American pop music. Ska, which developed in the decade's early years, features a frantic rhythm that closely resembles the polka's. Although the style has sometimes been a vehicle for social comment, its almost cartoonish beat is usually associated with youthful energy and lighthearted, even silly antics. Ska's playfulness mirrors Jamaica's optimistic spirit during the first years of independence; its biggest international hit was Millie Small's blithe 1964 single, "My Boy Lollipop."

The history of ska-punk actually begins in the United Kingdom in 1979. A group of bands, notably the Specials, English Beat and Madness, developed the "two-tone" sound, named after the musicians' desire to unite black and white audiences as they melded Jamaican and British music. These groups employed ska's jumpy beat but also incorporated elements of punk and music-hall, the British equivalent of vaudeville. In the United States, the impact of Britain's ska revival was limited but abiding. Today, there are scores of American ska-punk bands, which alternate passages of bouncy ska and aggressive punk. There's also a growing number of groups exploring ska's original sound, which was jazzier and less frenetic.

The development of reggae followed ska by a few years. Reggae had a slower, loping rhythm and an outlook shaped by political disappointments and Rastafarianism's critique of the modern world, which it calls "Babylon." The style produced few American hits but it was globally influential, in large part because of the appeal of reggae pioneer Bob Marley. During the mid-'80s, "toasters" (Jamaican parlance for rapper-deejays) like Super Cat incorporated hip-hop's beat-box pulse into reggae, yielding a style known as dancehall. Dancehall is enormously popular in Jamaica and has influenced American hip-hop and such British styles as drum 'n' bass, yet it has never reached a mainstream American audience.

Despite his significant cult following, few Americans heard reggae dancehall star Super Cat until last year, when California rock quintet Sugar Ray asked him to add his charismatic growl to one of its songs. The result was "Fly," which Billboard certified as last year's second-biggest modern-rock track. While No Doubt's 1997 hit was a traditional ballad, "Don't Speak," that contained not an ounce of ska, "Fly" brought the dancehall-reggae sound its biggest American audience ever.

"Fly" was merely the most-played example of a burgeoning style. Almost as prominent were such laid-back hits as Smash Mouth's "Walkin' on the Sun," 311's "All Mixed Up" and Sublime's "Santeria" and "Wrong Way." Their variety of Caribbean (and occasionally Latin) rhythms brightened the sound of the genre that radio programmers call modern rock.

The modern-rock format exists primarily in reaction to the unexpected early-'90s triumph of Nirvana, the Seattle trio that played a punk-metal hybrid known as grunge. Nirvana's most revealing song title was "I Hate Myself and I Want to Die," and the band's influence helped forge a new radio format emphasizing songs that, though sometimes tempered by irony, were mostly bleak: Pearl Jam's "Nothingman," Soundgarden's "Black Hole Sun," Green Day's "Basket Case," Beck's "Loser." Combining punk's dissatisfaction with metal's despair, this was not good-time music.

The new reggae-rock has exchanged grunge's psychic black hole for a sunnier outlook. In a sense, the easygoing sound is the latest incarnation of beach music. Of the new bands, all but Omaha's 311 are products of California; Smash Mouth is from San Jose, while Sugar Ray and Sublime both hail from the harbor and beach towns south of Los Angeles. Almost 20 years ago, the latter area was one of the crucibles of hard-core, which took most of its raw style and rough sensibility from British punk. Subsequently, the south-of-L.A. scene was shaped by the reggae experiments of such British bands as the Clash, as well as Britain's late-'70s ska revival.

Now the California groups that seem to have captured the popular imagination are mostly hard-rockers like Sugar Ray, Sublime and Smash Mouth. These bands generally employ lilting island rhythms for change-of-pace songs only. Those deviations, however, are the ones that have gotten the airplay.

Reggae-fied rock is not purely a '90s development. The Jamaica-spiced track has been a staple of singer-songwriter albums ever since Marley achieved a cult following in the late '70s. But such performers generally appealed to an older audience. Hard-edged post-punk bands like Jane's Addiction and Red Hot Chili Peppers were more likely to incorporate funk rhythms, while mid-'80s collaborations between rappers and metal guitarists presaged bands like Rage Against the Machine, whose thundering style translated Public Enemy's strident hip-hop to the guitar band format. Although Rage Against the Machine stresses political manifestoes over psychological recriminations, the L.A. quartet has two things in common with Nirvana: urgency and discontent. Whether its grievance was personal or ideological, the rock music of the early '90s was bruising and grim. It didn't crack a smile.

The new reggae-rock bands, however, can barely stop giggling. That might reflect what they've been smoking. When these musicians are interviewed, a bong is a typical prop. The headline on a recent Rolling Stone profile announced 311 as a "weed-lovin', good-timin', record-sellin' " band. The first couplet of Smash Mouth's "Walkin' on the Sun" is, "It ain't no joke/ I'd like to buy the world a toke." Sublime essentially ended in May 1996, when singer-guitarist Brad Nowell died of a heroin overdose -- two months before the release of the group's self-titled third album and first mainstream success. Yet when the band's survivors were interviewed by Spin a year ago, they too had a bong bubbling. Recently they released an album of outtakes, blithely titled "Secondhand Smoke."

The woozy sound of grunge suggests the effects of heroin, and the speediness of punk and ska is the musical analogue of an amphetamine rush. Despite the claims of many well-publicized reports, however, it's really impossible to keep track of shifting fads in illegal drugs, let alone how they affect pop music. Nor is there any reason to think that pot ever really went out of fashion: After all, the biggest-selling American punk band ever, Green Day, named itself for marijuana.

Sublime is more likely to lope than thrash, but its music is the natural successor to Green Day's most popular album, 1994's "Dookie." That was Green Day's most relaxed effort and it -- like "Sublime" -- includes plenty of songs about being young and listless (and possibly useless), as well as a few references to smoking pot. What Sublime added to the formula was a lot of reggae, including a sample from reggae poet Linton Kwesi Johnson (on "Garden Grove") that anticipates Super Cat's appearance on "Fly."

Where Green Day and Sublime offer a lackadaisical form of sociopolitical commentary, their successors are less inclined to complain. Whatever "Fly" is about, it's no protest song. And 311's "No Control" is sanguine about the sort of travails that supposedly killed Nirvana's Kurt Cobain: "How can you say that you're blue," asks singer Nicholas Hexum. "A rich star you are/ You know you still complain/ That's insane."

Such cheerfulness is not necessarily narcotic in origin. The audience for bands like Sugar Ray probably doesn't spend much time thinking about the upcoming budget surplus, but it's clear that most Americans are content with the current state of the union. "Still complaining?" 311 fans might ask. "That's insane."

The popularity of such songs as "Fly" and "Walkin' on the Sun" also reflects the emergence of the "echo boomers," the new generation of young -- and, demographers argue, largely untroubled -- teenagers who don't get the anger of the rock that appeals to their older cousins. This audience has been credited with the success of such unabashedly teeny-bopper acts as Hanson and the Spice Girls. Some of these kids surely also bought albums by sensitive young neo-folkies like Jewel and Fiona Apple, as well as the work of the sunny new reggae-rockers.

More cynically, the success of easier-going rock can be attributed to the newly rigid formats of modern-rock radio. Nirvana's success threw programmers into turmoil, and the result was a few years of relative openness. More recently, however, tight playlists have become the rule, a situation that favors songs that are tuneful, inoffensive and even familiar.

Sublime breached the commercial airwaves with "What I Got," a song whose melody echoes the Beatles' "Lady Madonna." The bouncy organ riff of "Walkin' on the Sun" recalls the 1964 Zombies hit "She's Not There," and the band's second single is a relaxed ska cover of War's light-funk 1975 hit "Why Can't We Be Friends."

If there's a period that these bands most consistently evoke, however, it's the early '80s -- the golden age, such as it was, of MTV. In that period, when most American bands weren't yet making videos, MTV turned to Britain and found such resolutely frivolous popsters as Duran Duran, Culture Club and Adam Ant. Sugar Ray covers the latter's 1981 tune "Stand and Deliver" on "Floored," while the new album from the not-very-punk ska-punk band Save Ferris includes a rendition of "Come On Eileen," the Dexy's Midnight Runners Celtic-soul hit from 1983.

Pop music trends are fleeting, and these days rock stardom seems even more so. Sugar Ray's "Floored" has often been called its debut, but the band actually made a 1995 album, "Lemonade and Brownies," that stirred little interest. Green Day's two subsequent discs have failed to rival the impact of "Dookie." 311's latest album, "Transistor," is a commercial disappointment. Smash Mouth's "Fush Yu Mang" is unlikely to herald a lengthy career. Sublime will never record again.

Still, reggae and ska's springy rhythms show no sign of losing their utility. As the beat of "Fly" fades, the happy young echo boomers will grow older and probably surlier, the nation's mood may turn ugly again and audacious new bands will challenge the orderly programming of modern-rock radio. Some of them will surely make fresh use of a Jamaican rhythm. CAPTION: The Might Mighty Bosstones, right, are indeed a ska-punk band, but Sublime, above, and Sugar Ray, below, are reggae. CAPTION: Sunny sounds: Smashmouth's Greg Camp, Steve Harwell, Paul De Lisle and Kevin Coleman.