Back in the early '60s, music was a man's world even for women singers. It was all "One Boy" and "Johnny Angel" and "I Will Follow Him" and "I Only Want to be With You."

Fifteen years and a social revolution later, women seem to have taken a big step - backwards. The top single in the country today is a lady's libidinous invitation to "Ring My Bell."

In fact, women singers have the top five records in America for the first time in memory, but it's no victory for feminists. Three of the five songs are explicitly sexual, another suggestive, one merely cute. And four were written by men.

The hits are Anita Ward's "Ring My Bell"; Donna Summer's double-header, "Hot Stuff" and "Bad Girls" at No. 2 and No. 3 respectively; Sister Sledge's "We Are Family"; and Rickie Lee Jones "Chuck E.'s in Love."

"Ring My Bell," "Hot Stuff" and "We Are Family" were all written by the artists' (male) producers. Summer has a one-fourth writing credit with three men on "Bad Girls." Jones alone is responsible for "Chuck E.'s in Love."

It seems a long way, baby, from the way we were. In 1972, as radios were proclaiming "I Am Woman" and scolding "You're So Vain," it seemed rock 'n' roll was going to liberate Peggy Sue and Mary Lou from the back seat and the beach blanket. Men were supposed to love women for their PhDs as much as their physiques. So how come Donna Summer is groaning for "Hot Stuff?"

It's because in 1979 - Woodstock plus 10 - music is cycling back to sexist rock in an age of the New Immorality: post-liberation role play; muskrat love; le lust de Cartier in gold and platinum sales. Women are singing about sex in the night and sex on the dance floor and sex on the street corner.

"Meet me at midnight," says Anne Murray. "Light My Fire," sighs Amii Stewart. "Hey mister, have you got a dime? If you have, I've got the time," suggests Summer. "The night is young and full of possibilities," insinuates Ward.

It's red-light rock, and it's so commercially successful that Helen Reddy has abandoned her "I Am Woman" invincibility to entreat "Make Love to Me" to a disco beat. And even Cher, once a master of the male put-down, is moaning "Take Me Home" and "Wasn't It Good?"

And if the omens are to be believed, we're in for a lot more of the same.

"The music industry happens to be in a strange sort of slump," says pop super-producer Phil Ramone, "and nobody's sure why. Records that were supposed to be big sellers aren't, and the only thing that has been consistent is the disco thing. So what's emerging is this disco crossover into pop."

"Men like to hear a woman's voice saying what men want the woman to be saying," according to Gay Talese, who has been working since 1971 on a comprehensive study of sex in America.

"It's exactly like the X-rated, hardcore porno movies that are written by men, directed by men and attended by men. The women in porno films are aggressive. It's a male fantasy. You'll hear Linda Lovelace or Marilyn Chambers or Andrea True talk in ways you will not hear in the raunchiest boudoir on the West Side of Manhattan."

Disco music, says Talese, is an aural kind of porno film. "Of course the beat is sexual, the rhythm is sexual.

"The whole fantasy is that sex is easy. In real life, it's not easy. If it were, there wouldn't be a multimillion-dollar industry in sexual services. And a record player playing this aggressive song is just one more way men pretend."

Talese also points out that only recently have women writers been able to be "sexually explicit - erotic, graphic, in ways that 10 years ago would have been considered pornographic legally and otherwise." As examples, he mentions Erica Jong's "Fear of Flying" and Judith Rossner's "Looking for Mr. Goodbar."

Giorgio Mcroder, Oscar-winning composer of the score to "Midnight Express" and Summer's producer-mentor says that the music industry, "as it is now," calls for female superstars: "The whole disco scene is related to girls as singles."

Robert Spitz, an industry executive turned-critic who has just finished a book on the Woodstock festival, compares the new sexuality in music to "jiggle television," suggesting that Donna Summer is the vinyl version of a Charlie's Angel.

Meanwhile, the sex wave in music is swelling around some of the "clean" singers who were beached a few years ago by the advance of feminism. Olivia Newton-John has been trying to harden her image, a turnaround symbolized by her bobby-sox-to-black-leather switch in the movie version of "Grease."

Ramone is doing some preliminary studio recording with Karen Carpenter, whose old image Ramone variously describes as "Miss Virgin America" and "Miss Clean Goody Shoes."

"I'm trying to take the syrup out," says Ramone, who also produces the individualistic Phoebe Snow.

"I tell her, Look, you're 28 years old. One of these days your brother's going to retire and your mother won't be standing right behind you.' You don't necessarily have to make a sexual statement, but you do have to make some statement of reality." CAPTION: Pictures 1 and 2, Rickie Lee Jones and Donna Summer: "Music is cycling back to sexist rock in an age of the New Immorality."; Picture 3, Anne Murray is part of the disco scene that has "women singing about sex in the night and on the dance floor."