WHILE mainstream pop music reverts to a juvenile frivolity that looks back in spirit to the late 1950's and early 60's, many of today's hits still convey very dark undercurrents. In its lyrics and in cold, mechanized dance rhythms broken by nervous electronic flurries that sound like miniature detonations, pop music is anxiously contemplating nuclear war.

There is, however, an interesting and perhaps significant difference between American and British points of view. Pop music, of course, isn't a scientific sampling of public opinion, but it is one index of the mood of young people. And, according to pop music, British youth are more anxious than Americans about nuclear issues. In American pop, nuclear war and the end of the world are often presented as an ultimate fireworks display - inevitable but exciting. Trans- Atlantic groups like the Police, U2, Culture Club, and Frankie Goes to Hollywood, on the other hand, are expressing a more fearful and realistic concern. Recently, both Culture Club and Frankie Goes to Hollywood enjoyed No. 1 English hits with explicit warnings about the horrors of nuclear war. Though heavily promoted in America, neither of these songs became significant hits here.

In contrast, the American attitude toward nuclear confrontation as revealed in pop lyrics might be best expressed by Prince, whose soundtrack album for ''Purple Rain'' has sold more than 9 million copies. The renegade rock-funk star from Minneapolis, whose taunting lubricity suggests a composite of Jimi Hendrix, James Brown, Little Richard, and Mick Jagger, flaunts a fatalistic nihilism that says, in effect: The end is near, and there's nothing we can do about it, so let's have fun.

In the hit title song from his last album, ''1999,'' Prince awakens from a dream in which the sky is purple and people are running in every direction. After contemplating the horror, the singer concludes,''War is all around us, my mind's prepared to fight, so if I gotta die I'm gonna listen to my body tonight . . . I'm gonna party like it's 1999.'' At the end of the song, a child's voice is heard asking, ''Mommy, what about the bomb?''

The presumption of imminent catastrophe also colors the songs on ''Purple Rain.'' The central image of the soundtrack's majestic title song has Prince and his true love reconciled just in time for the end of the world. Amid a cloudburst of nuclear precipitation (''purple rain'') they are united in the hereafter. In ''Let's Go Crazy,'' Prince impersonates a sidewalk preacher exhorting frenzied pleasure-seeking in the face of extinction: ''We're all excited, but we don't know why; maybe it's cuz, we're all gonna die.'' The song builds to a screeching hail of electric guitar and ends in an explosion. There's just no escaping the sense that Prince isn't merely alerting us to nuclear peril, he is lusting for doomsday.

Even Michael Jackson, who in pop's panoply of competing icons has been cast as Prince's opposite - the nice young man versus the rebel - evokes horror as a thrill. The songs on ''Thriller'' are suffused with a nightmarish paranoia. As a show-business symbol - an ageless, sexually ambiguous fusion of Peter Pan and ''E.T.'' - Mr. Jackson personifies a collective fantasy of an occult rather than a practical solution to the problems of the world.

The seeming difference between American and British attitudes toward nuclear confrontation is evidenced by the American record buyers' embracing of Prince's eschatology and Michael Jackson's escapism and its rejection of British pop songs with more exhortatory antiwar sentiments. After their second album sold four million copies, the British pop group Culture Club seemed on top of the heap in America. But their third album, ''Waking Up With the House on Fire'' is a spectacular dud. The blame can be laid largely on the commercial failure of ''The War Song,'' the album's first single, in which Boy George proclaims, ''War is stupid, and people are stupid, and love means nothing in some strange quarters.''

Frankie Goes to Hollywood, the English pop quintet whose disco song, ''Two Tribes,'' explicitly criticizes the arms race, also received a frigid greeting in America. After selling more than a million copies of each of two different singles in Britain, the group arrived here last fall bent on conquering the United States and was roundly rebuffed, and ''Two Tribes'' barely got a foothold on the American charts.

If the sales of pop records are any kind of indicator of youthful conviction, one might conclude that there is a fundamental difference in the American and British outlooks. American youth would seem to feel so powerful and prosperous that its pop culture can afford to be oblivious to real nuclear peril. Less economically robust, and with a far less rosy future, British youth are expressing their sense of vulnerability.

Will the Grammy Awards ever be more than a reflection of mass commercial taste? Not when the major category nominations are decided by a voting body of more than 5,000. At least this year's nominees for Album of the Year represent a fairly consistent degree of quality. The five candidates - Bruce Springsteen's ''Born in the U.S.A.,'' Lionel Richie's ''Can't Slow Down,'' Tina Turner's ''Private Dancer,'' the ''Purple Rain'' soundtrack by Prince and the Revolution, and Cyndi Lauper's ''She's So Unusual'' - have been critical as well as commercial successes.

The lesser categories, however, include some odd choices, e.g. Pia Zadora for Best Rock Female Vocal Performance. It also seems misleading for compositions that were published years ago to be nominated on the basis of new recordings. ''City of New Orleans,'' by the late Steve Goodman, was a hit for Arlo Guthrie in 1972. Should it be eligible this year for Best Country Song because of a new version by Willie Nelson? Based on a recent recording, Samuel Barber's opera, ''Antony and Cleopatra'' was also nominated for Best New Classical Composition. Does this work, which opened the new Metropolitan Opera in 1966 amid great fanfare, qualify as ''new?'' If so, freshly unearthed and recorded 17th-century classics could be construed as new compositions.

In other Grammy matters, the jazz trumpeter Wynton Marsalis received nominations in both the jazz and classical fields for the second year in a row. And this year, a long overdue category of Best Reggae Record was inaugurated.

The enormous influence a record producer can exert over a group's fortunes is evidenced by the extraordinary resurgence of the rock-jazz group Chicago. By the end of the 1970's, this horn-based septet was considered washed up. But after moving from Columbia to Warner Bros. Records and changing its management, the group, helped by the producer-arranger-keyboardist David Foster, dramatically revamped its sound. From a scrappy jazz-rock ensemble, Chicago metamorphosed into a sleek pop-funk band oriented more around synthesizers and keyboards than horns.

A master craftsman of Hollywood pop-funk, Mr. Foster collaborates on the songs as well as producing and arranging the group's records. While the band is still recognizably Chicago, their sleekly layered grandly orchestral sound is the pop equivalent of having shaped up for the 80's by sporting a new wardrobe, a gym physique and a trim haircut. Having already spawned three top-ten singles and sold more than two million copies, the band's newest album ''Chicago 17'' is fifth on Billboard's album chart and climbing. There's no end in sight.