At last glance, the Purple Kingdom of Minneapolis had locked up three of the top six slots on Billboard's R&B singles chart. Prince, the great purple one himself, held down No. 3 with "Sign 'O' the Times." Sheila E., Prince's percussionist and sidekick, was at No. 6 with "Hold Me." Andre Cymone, Prince's best friend from high school, wrote and produced the No. 1 song, Jody Watley's "Looking for a New Love."

For all its commercial success, though, a certain decay has crept into the Purple Kingdom. It's not just that Prince's own double album, "Sign 'O' the Times" (Paisley Park 9 25577-1), sounds more like unfinished demos than the major statement it aspires to be. It's not just that the album "Sheila E." (Paisley Park 9 25498-1) is more a collection of riffs than actual songs. Nor is it that the album "Jody Watley" (MCA 5898) exposes just how limited a singer she is.

No, the real problem is that Prince and his disciples have steadfastly refused to face up to the contradictions in their esthetic of sexual liberation.

When Prince first emerged as a major artist on 1980's "Dirty Mind," he articulated an esthetic of uninhibited sexuality in defiance of every taboo. That album and his three subsequent efforts gathered much of their power from the tension between his vision of unrestricted sexual play and the repressive forces of society (the prejudices described on "Controversy," the nuclear threat described on "1999" and the Freudian guilt described on "Purple Rain"). In 1984 he seemed on the brink of a mature statement about the politics of that conflict.

Instead, he shrank from the challenge into the fantasy world of psychedelia and soft-core. His more recent sexual fantasies seem disconnected from the real world; they seldom acknowledge the real emotional and social complications that come with sex.

Nor has he faced up to the contradictions between his rebellious sexuality and his increasingly reactionary political and religious commentary. Inevitably, his music (and his films) has become more self-indulgent and lightweight as his lyrics have retreated from the real world.

Not surprisingly, this weakness has seeped into the music of his disciples. Sheila Escovedo, the California Latin percussionist, emerged in 1984 as Sheila E. with "The Glamorous Life." That stunning album captured the tensions between poverty and fantasy, lust and friendship. Unfortunately, she quickly followed her mentor's retreat into fantasy with "Romance 1600," a sound track for an imaginary soft-core mini-series.

Her new album, "Sheila E.," is a lot better musically than "Romance 1600," but is undermined by the same escapism. Her new hit single, "Hold Me," is a slow-grind sex fantasy that features Escovedo's swooning sighs and orgasmic moans. She does it very well, but the song is really nothing but a guitar trio vamp with no real melody or musical shifts.

Most of the other songs are just as slight. "Koo Koo," which actually has the album's most ambitious lyric, is an electric drum pattern and very little else. "Pride and Passion" offers a half-spoken romance novel plot over a percussion groove. "Boy's Club" and "Hon E Man" are nothing but dirty talk with production tricks.

Escovedo may not be much of a songwriter, but she is a superb percussionist and a steadily improving singer. She pays tribute to her roots with the hot-pepper instrumental "Soul Salsa," which features both of her parents and three of her siblings. "One Day" and "Faded Photographs" both rock out convincingly.

The album's best song is "Wednesday Like a River," which boasts a solid chorus melody and respectable lyrics. The vocal flows lushly and patiently over the agitated rhythm track. Escovedo makes the most of it, hitting the high notes fully and conveying second thoughts about an affair once the passion has worn off.

Escovedo is a rarity in the Purple Kingdom -- a female vocalist who can actually sing. Her predecessors, Vanity and Apollonia, relied far more on their looks than on their vocal cords to sell records.

That seems to be the case as well for Jody Watley, who was a "Soul Train" dancer, not a singer, when she was recruited into Shalamar in 1977. When the group folded in 1984, Watley became a London model. For her debut album, she teamed up with Andre Cymone, Prince's guitarist and bassist from junior high through the "Controversy" tour. Cymone cowrote five songs with Watley, produced them and played almost all the instruments. The sound is classic Minneapolis -- booming electric drums and punchy synthesizers. The appeal of the hit single "Looking for a New Love" is the staggered dance beat and the bright staccato synth riff. It certainly isn't Watley's pedestrian vocal -- she can't even rap effectively. And it certainly isn't the jealousy lyrics, which were seemingly generated by a computer too.

Cymone's four other songs all reflect Prince's latest self-indulgent sex fantasies. Cymone has Watley exclaim that it's "Still a Thrill" when she and "Some Kind of Lover" "Do It to the Beat." Unfortunately, Watley's halfhearted mumbles don't generate the same heat as Prince's squeals. Cymone has a real knack for refreshingly inventive dance rhythms, but his melodies and solos are unimaginative at best.

Bernard Edwards, Nile Rogers' partner in the pioneering disco-funk band Chic, produced three of the other songs. Like Cymone, Edwards is far better with clever rhythmic patterns than with melodies. He produced Watley's duet with George Michael on "Learn to Say No," which finds Michael outclassing Watley (much as Aretha Franklin outclasses Michael on "I Knew You Were Waiting").

In this era when the denial of pleasure is proposed as the answer to every social problem, an effective advocacy of sexual liberation would be most welcome. Unfortunately, Prince seems unwilling, while his followers -- Escovedo, Cymone, Jesse Johnson and Morris Day -- seem unable. Nonetheless, a couple of defectors from the Purple Kingdom are picking up the torch.

Jimmy Jam and Terry Lewis, the former members of Minneapolis' the Time who have become the hottest producers in the business, have celebrated sexuality within a quite realistic context on Janet Jackson's "Control" (A&M, SP-5106), which they largely wrote and produced.

Jam and Lewis are honest enough to exclaim the real pleasures of "Nasty" sex, but also to acknowledge that issues of "Control" surround sex and that sometimes it's best to say "Let's Wait Awhile." Jackson's album is a manifesto proclaiming that a woman can enjoy sex and still make her own decisions about it. It's also a promise that some artists in pop music won't shy away from the complicated issues of sexuality in the '80s.