It has been dubbed the "Yuppie Express," the white-collar Red Line route rising like the consumer price index from Dupont Circle through Bethesda and White Flint.

But yesterday, as the four newest subway stops officially opened for business, the Red Line looked more like the Rainbow Coalition as members of all its varied constituencies, political and personal, turned out to test-ride the rail.

Senior citizens, children bundled to the nose and young suburban couples tucked red Metro pennants under their elbows and tied balloons to their wrists before clutching at the free doughnuts and hot drinks being offered to early riders.

"Give me an M!" urged Washington Suburban Transit Commission Chairman Carlton Sickles, and the pennants flapped. "Give me an E . . . . Give me a T! . . ."

A homemade sign at the Rockville station announced, "Welcome Metro At Long Last -- the M.C. Gray Panthers." Four-year-old He Lee, his hands full of subway paraphernalia, stood with his legs planted apart and a cardboard engineer's hat slipping over his eyes, as one of two subway Santas passed out balloons.

Even at 8:15 a.m., in a fog so dank it pressed the exaltation out of a hot-air balloon in the parking lot, there were dozens of passengers at the Shady Grove station, waiting for their first trip on the extension.

"I feel kind of silly," said a Gaithersburg man as he boarded for a free trip, "but I've been looking forward to this for a long time."

By 4 p.m., when fares were reimposed, Metro traffic spotters estimated that 26,500 area residents had taken advantage of the free passes.

What Yuppies there were -- young boys in Izod sweaters tagging behind their teen-aged sisters in stone-washed denim, young parents in boat shoes with back-packed babies -- seemed almost awed by the old-line political establishment being paraded up and down the Red Line.

"I'm going to White Flint," said 15-year-old Sarah Dumfries, "then I'm riding back and picking up my friends in Lakeforest Mall. I don't want to stay down there today -- my mom says all the politicians will be on the train."

There were politicians aplenty: about 300 officials, development representatives and Chamber of Commerce types who gathered at the Rockville platform for the official opening remarks.

For many of them, who have spent as long as 20 years hammering out the details of the system as if they were single nails, the extension of the subway out the booming I-270 corridor seems a personal triumph.

There were special citations for Sickles and longtime transit authority tactician Cleatus Barnett, "the Roger Maris and Mickey Mantle of the Metro system," in the words of County Executive Charles Gilchrist.

A dozen speakers -- Maryland Lt. Gov. Joseph Curran, state Comptroller Louis L. Goldstein, Sen. Paul S. Sarbanes, Rockville Mayor Viola Hovsepian -- extolled the Metrorail as a shot of adrenaline for job-seekers and weary commuters.

"Hear ye, hear ye!" called Sickles, ringing a cowbell instead of a conductor's clapper. "We're getting our Christmas present early. Welcome to our new train set."

"I was at the planning commission meeting in 1960 when they were trying to decided whether to paint the concrete," said Montgomery County Council member Esther Gelman, riding up from the Twinbrook station to the ribbon-cutting.

"I remember telling a friend of mine on the council then, Rose Kramer, that the one thing that terrified me was putting our money into the pot before anybody else. And she said, 'You gotta have faith.' Well, today we're riding on her faith."

Despite the pallor cast over the ceremony by the mist, the noise and sugar glaze of the promotional freebies lent a holiday atmosphere to the day's events.

There were live bands at the Rockville and Shady Grove stations, a remote broadcast by WAVA-FM at White Flint Mall, and a new subway slogan demonstrated by the self-consciously cherubic cheerleaders of Twinbrook Elementary School ("Metro is ride on!").

"This is very nice," nodded retired steeplejack John B. Bjornvick, who had ridden up from the District bearing Christmas gifts for his daughter and her family. "Could you get me a couple of those things?" he asked, motioning toward the pennants.

As lunchtime approached, and the fog finally began to fray, the windows of passing subway cars began to fill up with faces. With the formal scissoring of the bunting, the cartons of doughnuts and helium tanks were whisked away, and the riding began in earnest.

"It's not a very scenic route, is it?" commented a Shady Grove denizen, gazing out at the back lots of light industries lining the rails.

But for many passengers, it was just sightseeing. Older riders in particular spoke of riding all the way to Silver Spring and coming back without ever leaving the stations.

And despite the free one-way tickets, White Flint and Rockville Pike shoppers took their cars as usual. According to Montgomery County police, the pike was "just about as busy as this time last year."