It is four o'clock on a Friday afternoon and you are waiting for a bus. You might be a shopper with packages that are getting heavier by the minute or a student with too many books. Or maybe you just got off work and all you want is to go home and relax. It looks as if the bus will never come.

Suddenly, a tape recorder starts playing music, and a petite, blond-haired young woman in a Metrobus uniform and Metrobus replicas on her feet begins to dance. Right in front of you at the Metrobus stop.

It may sound like a mirage, but it actually happened last Friday at the Friendship Heights Station in the Chevy Chase Shopping Center. Dancer Carol Vaughn, wearing the secondhand Metrobus uniform decorated with a courtesy award and a Metro badge, began tap dancing on the sidewalk in her specially designed Metrobus shoes.

"I couldn't figure it out at first," said Doug Larabee, a visitor from Fresno, Calif. "I thought she worked for Metrobus. It's good advertising for Metro - except when I asked for her what bus to take to the Capital, she said, 'I don't know.'"

"I like to work outdoors," explained Vaughn, who has choreographed and performed dances on steps and fountains as well as at Metro Center just before it opened in 1976. "It's my favorite way to dance because you can see reactions so easily on people's faces. On stage you're usually blinded by lights. It's nice to be able to see people's reactions and play off that."

The initial reaction from almost everyone was surprise. "I was really surprised - I mean, I didn't expect to see somebody dancing," said Cecilia Fant, a Washington resident who frequently takes the 34 bus up and down Wisconsin Avenue. "But I thought she was wonderful - her dance steps were so good."

Vaughn, co-director of Feet First, a Bethesda-based dance company and studio, choreographs her outdoor dances as carefully as a dancer working with conventional space. For her Metrobus dances she combined jazz and tap to develop steps suited to her rather bulky shoes.

The shoes were designed by Washington artist Peter Coates, who constructed latex rubber replicas of Metrobuses and stuffed them with foam rubber. The shoes were pulled on, like bottomless galoshes, to fit over a regular pair of tap shoes.

Vaughn is not paid by Metro, but does her dances in her spare time without pay from anyone.

For her bus stop numbers, Vaughn included a number of Metrobus references. Executing a side-to-side movement, she said: "This step is called a sway step. It's what you do when you don't have a seat on a bus." Bending forward on her Metrobus shoes she did a kneeling step, in honor of the new kneeling buses that will lower boarding platforms to a level even with the sidewalk.

After dancing at the Friendship Heights Station, Vaughn boarded a 34 bus to Georgetown. It was too crowded for dancing, but her shoes caused a few comments.

"Hey!" called a passenger. "One of your bus drivers has something on her feet. How is she going to drive?" He shurgged his sholders. "Oh well, I guess it's good that the company is hiring women drivers."

Getting off at M and Wisconsin, Vaughn did some more dancing and talking. To a couple of girls: "Do you tap dance?" No, they said, because they were too tall. Without missing a step Vaughn replied: "All you have to do is find a Fred Astaire who's tall."

Spying a young man stuck in commuter traffic, Vaughn called to him: "Get out here and wait with us. Come on - here's a single woman waiting for the bus who doesn't have anybody to wait with her." Laughing, he called back: "Can I borrow your shoes?"

When asked what she hoped to accomplish Vaughn said: "Most of my pieces are an attempt to show people's new side of a site that they haven't seen before. Maybe a year later somebody will be at a bus stop and they'll say, 'Remember the time that gal wore those crazy shoes?" Maybe it will make them feel differenty about commuting."

Vaughn added that she hopes to tap dance on water in the spring, if the design for a floating platform can worked out. She said she also is thinking about tap dancing to New York and back on a train.

Vaughn decided to wind up her dance and board the 30 bus in Georgetown for Pennsylvania Avenue. A blue van moved by in the rush-hour traffic. It's driver, catching the last of Vaughn's dance, rolled down the window: "A-all ri-ight!" he called as the light changed and he drove off.