The temperature dropped. The weather forecaster promised snow. Miles of local hiking trails were deserted except for an occasional jogger or cyclist.

And yet, dozens of Northern Virginia residents pulled on sweaters, hats and mittens last week and headed -- where else? -- indoors for a chilly spin on the ice skating rink at Mount Vernon Recreation Center.

The popularity of indoor skating in the winter, as opposed to the summer, has stumped Bill Hellwig, the recreation center manager. "Even though we've got an indoor rink, our skating time follows the seasons," he said with a shrug. "I guess people think: 'Oh, it's wintertime. Let's go skiing, skating and drink hot cocoa.' "

In the lull of long, hot summers, Hellwig has resorted to building snowmen on the side of the road with leftovers from scraping the ice rink to remind people that the rink is still there. "On a 100-degree day, we'll put a little sign in the snowman's arms saying, 'Come skate with us.' "

But this is wintertime, it is cold and dreary outside, and the refrigerated rink owned by the Fairfax County Park Authority is busy 21 hours a day -- from 5 a.m., when the first skaters lace up for lessons, until about 2 a.m the next morning, when the last hockey league team drifts off.

The earliest birds are figure skaters, who work to perfect their figure-eights and freestyle dance routines both before and after school.

Derrick Delmore, a 12-year-old figure skater from Fort Washington, starts skating at 7:15 a.m. each morning and resumes skating after school. He recently won a prestigious regional skating competition, enabling him to compete in a national competition for intermediate skaters. "I don't know what really draws me to it," he said. "It's a good way to set goals for yourself."

About 9:30 a.m., after figure skaters leave for school and before hockey players arrive to rip up the ice, a small but steady group of senior citizens often takes over the rink.

One recent morning, Dorothy Colbert, of Fairfax County, and Chevy Chase resident Jeff Crockett glided arm in arm around the rink to the rhythm of a waltz. Meanwhile, Fairfax County resident Daryle Baxter preferred to dance by himself in the center of the arena, carving circles with one foot, then the other.

Baxter, 68, said he hadn't skated in years when he decided, after retiring from the military several years ago, to take skating lessons. Now he wishes other senior citizens would try it. "So many people my age, they are reluctant. But you can't go out there just one time," he said, because then the only accomplishments will be that "your feet hurt and you fell a lot."

Baxter said he loves skating because "it's so graceful. It's work, but it appears to be effortless."

On weekday afternoons, the rink belongs to youth hockey teams. The success of the Washington Capitals in recent years has swelled the ranks of the Northern Virginia Hockey Club to about 360 boys and girls this year. About 100 additional children were turned away.

"We're at a point where we're crowding people out of the sport. The demand has exceeded what we can supply," said Hellwig. To meet the demand for more ice, the Park Authority plans to build an indoor rink in Reston by 1995. There are only two other rinks in the county: the Fairfax Ice Arena in Fairfax City and a seasonal outdoor rink at Reston Town Center.

Because the demand for ice time is high, local adult hockey teams typically pay up to $130 an hour to rent the Mount Vernon rink, and hockey players must be willing to play at odd hours.

Joe O'Connell is one such hockey player. Hours after his work day has ended, the 32-year-old interior designer drives to the rink from his Arlington home and pulls on his skates. "Sometimes, that's all you do is work and play hockey," he said.

"When I was a kid, there were two things I didn't want to do: be a catcher or a goalie," said O'Connell. Now he enjoys being a goalie 15 hours a week. "It's an emotional position because your mistakes go on the scoreboard."

For years, Jim Tabellario, a 51-year-old computer specialist from Burke, has played pickup hockey at 10:15 every Thursday night with players of various ages and levels of experience. "Part of the attractiveness of our night is it's strictly carefree -- no whistles and no referees," he said.

For die-hard hockey enthusiasts such as Chris Holland, of Alexandria, and Bethesda resident Patrick Duke, the rink offers pickup hockey at lunchtime several times a week. "I run a bar at night. I sacrifice three hours of sleep to come here," Holland said.

Duke, a consultant for Blue Cross & Blue Shield who plays hockey in local leagues, showed up for his first lunchtime game recently wearing a tie and suspenders. Although he usually takes a long lunch hour from work, he said, "now I'm putting it to good use."

At the end of the week, a driving dance beat transforms the rink from a sports arena to a busy dance hall for families and throngs of teenagers. Most of the skates worn in the crowded arena are the brown or blue kind rented from the locker room, and the line to the snack bar is long.

The rink is a popular hangout for teenagers because "it's between this and the mall," said Rob Carbonello, 18, of Alexandria.

"It's different from going to see a movie. We always go to movies. It's different," added his friend, Leigh Franklin, 15, also of Alexandria.

Just then, a blond youth the size of a college football player lost his balance and skittered through the crowd, arms flailing, to crash into an arena wall.

"It's also very entertaining," Franklin said.