"Do portraits," suggested dealer Harry Lunn to art-photographer Joyce Tenneson, after the photo market took a nose dive two years ago. "And start with Nancy Reagan. She's the key."

"He was half-kidding, of course," recalls Tenneson.

"I wasn't kidding," says Lunn. "Joyce had done a number of portraits, but they were mostly of herself, and--to be cynical--her technique is amazingly flattering to anyone over 35. There was a whole new group around the Reagan White House, especially people of a certain age, and they all had money. But there was no portrait photographer in town with a particular flair and style--there was a vacuum."

Horror vacuii, Tenneson set out to fill it, and put out the word through friends that she was seeking portrait commissions at $250 each, even though since her one-person shows at the Corcoran in 1974 and at the Phillips in 1980, her prices had climbed to twice that amount--on the rare occasions when they sold.

"I couldn't believe the response," says Tenneson, a photography and art teacher here for more than 12 years, most recently at the Corcoran. "Within a month I went to $350, and in two months to $500, then to $750."

One hundred portraits later, Tenneson gets $800 per sitting in Washington and $1,200 in New York, Paris, Milan, Houston and Dallas, where her various dealers have waiting lists.

Nancy Reagan didn't have to wait.

Heady with success, Tenneson approached the first lady through White House photographer Michael Evans last year, and a session was arranged in December. That portrait is one of several in Tenneson's new show, which opened yesterday at Marie Martin, Washington's newest photography gallery, 3243 P St. NW.

The event also celebrates the handsome new book "Joyce Tenneson Photographs," just published by David Godine. As far as Tenneson--and most others--can remember, it is the first commercial book to be devoted to any Washington woman artist.

"This is the end of an era of hard work in Washington and the beginning of liberation," says Tenneson, who gave up entertaining two years ago, gave up cooking one year ago and saw her income quadruple last year. "Now I know I can make a living anywhere."

Tenneson's portraits are more than flattering, though they are surely that, with incipient wattles and other cosmetic shortcomings bleached out in an otherworldly white light. The high-key effect is reinforced by the fact that the portraits are printed on heavily textured paper prepared by Tenneson with delicate washes of photosensitive silver emulsion. Some look like fine pencil drawings.

But the best portraits are also intense psychological studies of states of being, distillations and extensions of her characteristic photographs of herself, her friends and children, undraped or draped in swaths of gauze or lace or tulle, all dissolved in an ethereal light.

One of the most haunting portraits--and haunting works--she has ever produced is that of a young Dutch woman, her head wrapped with lace in the manner of a painting by Vermeer, her eyes mirroring the pain of her husband's long illness and impending death.

If one of the central problems in Tenneson's art has been her obsessive self-preoccupation--and the attendant inability to express empathy--portraiture seems to have helped her over that hurdle.

"As a portraitist, I'm the opposite of the kind of photographer who stands back and says, 'Let the person reveal himself,' " says Tenneson. "When I know there's something inside, I try to bring it out. People tell me incredible secrets."

So do her photographs.

She brought tears to Nancy Reagan's eyes during the pre-Christmas session last year in the Lincoln bedroom at the White House.

"I told her to think of something that was terribly important to her at that very moment, and she teared up," says Tenneson, who diplomatically averted her gaze until composure was regained. She also resisted the temptation to capture the moment on film. "I think that would have been disrespectful," she says.

In the portrait Mrs. Reagan selected and approved for the show, she looks like a smiling schoolgirl. In Tenneson's choice--not on view--she has the look, Tenneson says, of a "hurt sparrow with large and profoundly sad eyes."

"I've found one thing about the portrait business that bothers me," Tenneson says. "Often you get a client who only wants the surface. I let them go through my portfolio to get a sense of what they want--after all, it is a commission. But from now on I'm going to tell them that I consider a portrait a work of art, and that I don't consider it a surface-flattering kind of experience. I'd like to show character and depth, and if they're not interested in that, they should go someplace else.

"I got a run of ladies in Houston who just wanted me to make them look younger, and though the paper gives it a soft look, it's never enough. It's never enough, and I'm not a plastic surgeon."

"Now I'd like to do more men," she says. She has already done Harry Lunn, Museum of Modern Art curator John Szarkowski and Washington filmmaker Richard Basch, who has made a short tape about Tenneson to go with her show. She's developed for them a style with more contrast. "But she has not found a way to cure baldness," warns Lunn.

Success and hard work have been something of an obsession with Tenneson since the days of her youth, so this moment is especially sweet. Her father's name was Alfred Tenneson, not as in Alfred, Lord Tennyson, but as in "Alfred, bring the car around and pick up Sister Alphonsine at the left portico."

"We lived in a convent, the poorest family in the richest neighborhood in Weston, Massachusetts," says Tenneson, who picked up a bitter edge from the experience, now softening at age 38. Her father was groundskeeper and chauffeur, her mother a secretary.

"When I was a kid, they had a PA system, and I'd be in class trying to work and all of a sudden I'd hear 'Alfred! Where are you! Sister Alphonsine is still waiting.'

"The girls would stare at me. It was humiliating."

In 1980, after 13 years as Joyce Tenneson Cohen, Tenneson reverted to her maiden name, without changing her marital status with her husband, a psychiatrist.

"I've always loved my name," she explained, "and others did too. It made me feel like I had something. Even as a kid, when bad things happened, I'd go into the woods and scream my name as loud as I could, until it hurt inside. I'd cry, of course, but then I'd feel good, and say to myself, Joyce Tenneson, you're going to be somebody some day."

And now she is, and a distinctive somebody at that--in her life as well as her art, which are all of a piece. Though she has technically left the church behind, its arm is long, and her home is a secular shrine of sorts, filled with feathers and birds' nests and votive lights and toy churches and swelling cathedral music. Given that context, it is no surprise that even an antique doll in a photograph of her son Alexander takes on the look of a guardian angel. Visitors to her show will get the drift, for Tenneson has made poster-size photographs of her home to give some sense of its ambiance, and has also transported some of her favorite props. They look like reliquaries even in the gallery.

Men tend to see in Tenneson's lacy photographs the quintessence of femininity, pure and inaccessible. But women are likely to find them inaccessible too, for the lace is not that of the boudoir, but of the christening gown, or a first communion.

Tenneson has mastered worldly ways as well, including the art market, which she will vigorously attack next week in promotion of both her art and her book--a book that follows by five years her highly successful anthology of self-portraits by female photographers called "In/ Sights," also published by Godine.

On Nov. 8, there will be a show and book signing at the museum shop-gallery of the International Center of Photography in New York, to be followed in January by shows in Houston and Dallas. From there Tenneson will go to Europe, where her book is being released in French, and where four exhibitions are planned in France, Switzerland and Italy.

"You've got to be tough in this business," says Tenneson. "If I thought I could only be an A-minus artist, I'd get out and save the pain. I'm in it for the whole thing."

She made the point when she had the chutzpah to invite Museum of Modern Art curator of photography John Szarkowski, keeper of the gates to fame and fortune, to her studio for a sitting after meeting him at Lunn's. "He came, and after the sitting said, 'I'll bet you want to get right in the ring with Edward Weston and the rest of them.' "

"You bet I do," she said.