Heidi Lammi is not extravagant, usually.

But when the Fairfax resident walks down the Miss America runway in Atlantic City, N.J., tomorrow night as Miss Virginia, she'll be wearing a $150 swimsuit that's useless in water.

Not only that, but she flew all the way to Texas to buy what she calls the "royal blue supersuit."

Basically it's a girdle. Designed with a V-neck, an emphasizing band under the bust, and cotton lining that does not hold its shape when wet, the swimsuit will likely capture the attention of the 55 million television viewers expected to watch the pageant.

"Some people say it's degrading to parade around in a swimsuit, but I look beyond that," Lammi explained at a recent interview in Alexandria. "It takes discipline to keep the body in shape and it's crucial for Miss America to be physically fit."

The George Mason University graduate is 26, 5 foot 5 inches, 105 pounds. She has perfect posture, perfect pink fingernails, and perfectly applied raspberry swirl lipstick. During two hours of being photographed and interviewed, not a single strand of her blonde hair moved. It's easy to believe she could walk into a windstorm and emerge groomed for a photo session.

"I always thought they were plastic," Lammi said of pageant queens. "But they're not . . . . The majority are down-to-earth and talented."

Lammi's competition will include Miss Maine, who on her biography lists "collecting blueberry memorabilia" as a hobby and mentions she was once a member of the "Crowned Potatoheads of Maine."

Miss Montana does "contortionism exercise" to relax and Miss New Jersey apparently wants people to know that she "owns a pink 1970 VW 'Bug' convertible in mint condition" because it's listed on her biography.

Under scholastic honors, Miss New Mexico mentions she was declared "Most Beautiful" in high school.

Other 1987 state representatives of womanhood: Miss New York, who notes on her biography that she is "fascinated and amused by the many blunders and bloopers" contained in the final version of one of her favorite movies, "The Wizard of Oz," and Miss Florida, who has a duck called Daffy as a pet.

During the talent competition, Lammi will perform a classical ballet routine, wearing a ruffled shirt and hair ribbons, to music by Louis Gottschalk. Miss Pennsylvania plans to sing an Italian aria and Miss Vermont will play the drums.

The two other local contestants, Tammy Alaine Walker, a 21-year-old Towson State University senior representing Maryland, and Cheryl Chapman, a 21-year-old junior at George Washington University representing the District, both said they will sing.

"Oh sure, we compare," Lammi said. "You think, oh, she has bigger eyes. She looks better in a swimsuit . . . . But I just concentrate on what I'm doing. Confidence is so important."

Since she won the state title in April, Lammi has driven around in a white 1987 Thunderbird (provided by the state pageant) with huge blue seals on the doors that read "Miss Virginia, 1987."

"A lot of people wave and honk," she said. "Some guys hold up signs with telephone numbers on them." One time, a man in southern Virginia rolled down his window, stuck a video camera out, and taped her driving down the highway.

In the past few months, the number one question from admirers is, does she have a boyfriend? She tells them: "No."

Born in Astoria, Ore., a town of 10,000 north of Portland, Lammi lived most of her life in Oregon, and was a runner-up in the Miss Oregon pageant twice.

Her father is a commercial fisherman in Oregon and her mother, who was born in Finland, works at home.

When she moved two years ago to Virginia, where her sister lives, she lost 20 pounds and her pageant luck improved. Along with practicing her ballet routine for hours at a time and watching her figure by eating only bananas for breakfast, she has been gearing up for tomorrow night through a series of mock interviews.

Friends, and even people she does not know, have asked her questions, to test her knowledge of current affairs and her ability to think quickly. She keeps time of how long she takes to answer and sometimes videotapes the practice interviews. She said, "I've been boning up on political affairs and the Persian Gulf, but who knows? They could ask something about AIDS or air safety."

Her swimsuit is packed, her hair doesn't budge, and her talent is well rehearsed. She says she's ready.

But, she points out, anything can happen when someone wearing a tight, pink evening gown and three-inch heels starts walking down a runway.