Not every hot singer whose seven albums and 16 singles have sold 25 million copies worldwide would be happily schlepping around the country; off the concert circuit, suffering on-the-air calls from fans who want to know how old she is (29), if she's married to Elton John (definitely not) and whether she's as Breck-blond pretty as her album covers (yep).

But Olivia Newton-John is searching for the magic formula that will put her voice back at the top of the pop charts. Even though her records continue to sell to the juicy tune of $7 million a year for MCA records, there is some concern that time off from the studio to cultivate Hollywood in the coming movie "Grease" may have cost her fans.

Company officials get antsy whenever a big name like Olivia hasn't had a million-selling single or album in two years; they fret over elusive Top 40s fame. They know that to radio program directors, baby, any hint that your song might make listeners turn the dial, no matter how blue the eyes, sunshine blonde the hair, or girl-next-door-wholesome the image, you're off the air. Business is business.

"The question I always ask myself is, 'If I play her song, will it tune in more people than it tunes out?" says Jim Elliott, bearded music director for WPGC, the Avis of local Top 40s station.

"Two years ago all the record companies had to do was hand you Sedaka, Captain and Tennile, John Denver, The Carpenters, Frankie Vallee or Olivia, and bingo! Now you couldn't get them arrested on Top 40," Elliott says. Take Olivia:

"She's got from what we call 'active listener acceptance' to passive, which means she's liked by a lot of people who say, 'Oh, Olivia Newton-John, isn't she sweet,' but who wouldn't go out and buy her record."

It simply doesn't matter that she once burned up the charts with, "Let Me Be There," "If You Love Me, Let Me Know," "Have You Ever Been Mellow" and the rest. Or that every album has either turned gold (1 million sales) or platinum (1 million units sold), or that her eighth, a "Greatest Hits" repackaging effort, is expected to turn gold by Thanksgiving day, when 200 radio stations around the country, including WPGC, will air her two-hour special with guests Peter Frampton, Shaun Cassidy, Karen Carpenter, Alice Cooper and Kiki Dee. Or that she has won three Grammys, was elected the Country Music Association's top female vocalist in 1974, reigns as a queen in Japan and Europe and may well be the most popular singer in the world.

Ancient history, sniffs Elliott, leaning back in jeans and a "So What?" T-shirt. "Once you've cooled off, you've got to prove yourself all over again."

Which is why Olivia herself, idolized as the Fawcett-Majors of love songs, has hired Scotti Brothers Entertainment of Los Angeles, the same ultra-slick marketing men who dusted off Barbra Streisand and The Beach Boys, sent the Osmonds into every home and made pat Boone's daughter, Debby, 19, a star. Among other things, the brothers have advised her to sortie from the ranch above Malibu, abandoning six horses, three Great Danes, one Irish setter, a cat and (on-again, off-again) boyfriend/manager Lee Kramer (It's back on") to staddle a stool in the WPGC studio and field questions from listeners, live and on the air, and drown the Heartland in sugar and spice.

"I have a little surprise for everybody," croons DJ Dave Fox: Olivia Newton-Johm has come to Bladensburg.

"Is that your real name?" asks a caller. (Yes.) "What was your first hit?" asks another. (Dylan's "If Not For You.")

And the public comes to learn that: Olivia sounds like Twiggy when she talks and giggles after each answer, was born in England, where her father taught at King's College, Cambridge, and moved to Melbourne at five; won a local "Gong Show," had "nightmares" after dropping out of high school at 16 to pursue singing, blossomed later in England, wilted momentarily, bloomed later in the States; doesn't feel "any desperate need" to meditate or do yoga, cavorts with her animals if she needs to relax and doesn't use booze or drugs.

As she sits, very composed in white corduory jodhpurs and boots - neither terribly profound nor the insipid Barbie Doll that detractors would have you believe - the console phones don't exactly explode like firecrackers: "flicker" would be more like it. And between questions, she closes her eyes, snaps her fingers to music emanating from headphones, rhythmically twitches about and squeaks, "Yeah, yeah . . . ta, dah," very off key.

Suddenly, it's all over, and a young technician bounds into the room, "Olivia, I met you in Germany when you came on the Armed Forces Network and you kissed my roommate's wrist and it's still the high point of his life!"

"Oh, that's nice!" she says later, musing over such incidents back at the hotel. "It amazes me that I make some men nervous. Some guys actually tremble when they shake my hands."

She doesn't know why; it's just seems to go with her cheerleader image as the fantasy sweetheart of every all-Americans male. "People come up to me and say, 'You look like my sister or my girlfriend.' I must have one of those faces. But I don't consider myself overly glamorous. I haven't worked at an image."

Yet The Image remains as essential as The Voice in the (Re) Making of a Star. And no one is more conscious of what face goes before the public than Olivia Newton-John, who this particular afternoon turns away a newspaper photograph seeking a "natural" portrait.

"She doesn't like surprises," says an ever-present PR woman. "Wouldn't you want to look your best?"

And Olivia squeezes a lime into her Perrier and proceeds to discourse on a variety of topics.

On men and her success: "A lot of men find it hard to cope with a successful woman. I try to make it easy as possible, but what I represent sometimes scares them away. I don't have any complaints."

On Nashville's resentment after she crossed over the pop charts in 1973 to walk away with country music awards: "I was a foreigner who had a country record written by an Englishmen . . . Besides, a lot of country artists come from poor backgrounds, where they didn't have anything to eat or wear. They've suffered. They know what they're singing. I can't relate to that kind of thing because I didn't go through it. But music doesn't have a passport, it can come from anywhere. You don't have to be black to sing soul or be from Nashville to sing country."

On John Travolta: "He was a terrific help to me on the movie set, very patient. We spent a lot of time together, but we're just friends."

On the women's movement: "I'm not a feminist because I've always felt liberated. I never felt a need to fight for women's rights because I've never had to put up with any of those problems. For women who have to, I sympathize. I believe in equal pay for equal work. They should be able to call themselves 'Ms.' But there's a way of doing it without going over the top."

Yet a mention that she's 29 and single brings on a feminist groan. "Everyone's so concerned about my being married," she groans. "Australia's been worried for years. But it's a very individual thing. I'm not for it or against it.If you're happy being married, that's great. Do I want to? Yeah, but when I get married, it's gonna be for keeps and to start a family. So I'm not rushing into anything. If I get married, it will be the strongest commitment I've ever made to anything, so I've got to be sure."

For the moment, now, she's most committed to her comeback. "If I knew the formula," she says, "I could go out and have No. 1 hits all the time. Sure, I was hotter before. It's a bit depressing, but you've got to have the downs to have the ups. In the industry, they call it 'a cold.' I hope to warm up, starting now."

And Olivia Newton-John takes the elevator down to the Georgetown Room at the Washington Hilton, where a hundred record salespeople and DJS, a few reporters, two Scotti Brothers (Tony and Ben, formerly of the Redskins via the University of Maryland) and one fund-raiser from the Democratic National Committee are waiting. And as she sweeps into the room, the flashbulbs pop and everyone puts down the drinks and ceases chewing at the lavish buffet long enough to rush over and have their picture taken with the star.

As one touped sales rep put it to her, "It's for my teen-age girl, Olivia, she just adores you."