It's Friday evening at 6 o'clock. Kay Casstevens, a lawyer on the staff of Sen. Tom Harkin (D-Iowa), is ready to put all paper work aside. After a hectic week of congressional hearings, legislative committee meetings and lobbying, Casstevens declines an offer from her colleagues to celebrate the week's end at the local "Friday night spot."

Instead, she jumps on the subway, gets off at the Bethesda Metro stop, and walks two blocks to the Feet First dance studio at 7649 Old Georgetown Rd.

On Fridays, about 25 advanced tap enthusiasts, including students and business professionals, flock to the glass-filled studio for a two-hour session of leap shuffle, step-ball-chain and sweat. They are part of the more than 250 adults from the District and Maryland who come to the studio each week for tap lessons.

The big-band music of George Gershwin blasting from the speakers, coupled with the sound of syncopated dancing feet, evokes great nostalgia for some. For others, it's the fulfillment of a longtime fantasy.

"I love this class because I always wanted to be a dancer . . . and this gives me that chance to do something totally different from my profession," said Casstevens. "You have to concentrate on tap dancing, which helps you to forget about your frustrations. I get totally absorbed."

Dee Jubb, a secretary for a consulting firm by day, said her two years of night classes with Feet First have been a way of "keeping my sanity. As long as I'm dancing, I'm happy and I get to release a lot of steam."

The center offers daily instruction in tap and jazz technique and is open to people of all ages. Fees range from $9 per class to an annual rate of $392 for four classes a week.

Richard Donohue, a trial attorney at the Federal Trade Commission, said that after several months of waiting outside the studio for his wife, he "decided to go ahead and take the plunge."

"I must admit that at first, I was a little skeptical {about taking the classes} because I have size 12 feet and I didn't want to appear to be a clod. But deep down inside, I think everyone wants to be a tap dancer." Donohue was a beginner seven years ago; now he's an advanced tapper.

Instructors say enrollment for the adult tap classes has steadily increased during the past five years, a trend they attribute to the reappearance of broadway musicals such as "A Chorus Line," "Ain't Misbehavin' " and "The Cotton Club."

Why are people from all walks of life investing time, energy and money to pursue tap dancing?

According to First Feet choreographer and artistic director Brian Donnelly, "some use it as therapy. It's a great release physically, and people get highs off of it."

Donnelly, who has performed in off-Broadway productions and abroad, said instructing a group of mostly adults "is different from teaching at some little dance school. To see these people dancing is very inspiring and gives me the juice I need to proceed on because they are dedicated."

When D.J. Foster helped start Feet First 10 years ago, the desire was to offer dance classes to a cross-section of professional people who either had a specific interest in tap or jazz dance, or who wanted to use the classes as a recreational outlet.

In 1977, there were two instructors and 27 students.

Today more than 600 children and adults are registered for the 14-week fall session, which began Sept. 9, in tap, modern or jazz dance, with six instructors.

"We have people from all walks. They mingle and get close to each other in the unified spirit of dance," Foster said.

"When you dance, there's a chemical released in the body called endorphine. This produces the most wonderful experience you can have . . . and you can see the joy on their faces during that one moment of total freedom," she said of the students.

Cara Macrina, an instructor of beginning tappers, said, "A lot of the people who come here have high-pressure jobs and they just want to let it all out."

Macrina said that no matter what the level of the student, she uses a psychological approach to instruction. "No one feels they have to compete with each other . . . they applaud for each other and that's a real sense of community," she said.

"Some people have the psychological feeling that they've never been able to accomplish anything. When they come in here, they can see the results they create right away. It's very gratifying and very rewarding," Foster said.

Irene Zevgolis, 27, a graphic designer, has been taking tap classes at Feet First for three years.

She said, "Every time I come here I get a renewed sense of energy . . . . I feel free. And Brian doesn't only teach you to dance, he teaches you how to perform."

Throughout the year, the student company dancers take their act on the road with an array of public performances and television appearances.

Guest artists such as Mercedes Ellington and choreographers from the Alvin Ailey American Dance Theatre and the Dance Theatre of Harlem have graced the studio floors. The company will be performing its fall showcase in late December.

But according to some, the glitter and glamor are secondary to other benefits of the dance classes.

Lisa Leake, a fashion consultant whose husband encouraged her to enroll in the classes, said: "For me, dancing is healing on a practical level. Each class helps me to escape from being so serious about life in a positive, healing way. Some people go to happy hour . . . I go to dance class."