Camille Conroy has this thing about trolleys. God help you if you are from Philadelphia where they still run the things, for Camille will be on you like an insurance salesman after the nuptial announcement and she will want to know precisely which trolley it is that goes to your house and all the details and she is not easily deterred.

Before leaving for a trip to England this summer, Camille's parents asked what they might bring back for her.

What else?

"A trip to Philly."

Camille, a Montgomery College student, shares this mad passion for old transit vehicles with about 200 other persons locally and around the country. They count themselves members of the National Capital Trolley Museum. In the sweet-smelling Montgomery County countryside between Wheaton and Olney, the museum is a place where streetcar fans young and old escape smog-congested notions of urban transport as we know it for better days of clang, clang, screech, screech and "Tickets, please."

The museum, its station house, two car barns, 12 trolleys and its two mile meadowland loop of track, all are run by its dues-paying members. On any good weekend you'll find a bunch of them sweeping, painting, sanding, mending, and, from noon to 5, spinning around the circuit in one or two of the old cars, escorting visitors into that land where musing melts into dreams.

But not this coming Sunday. This Sunday, from 1:30 to 3:30, everything that can run and hold passengers will pull out of the barns and onto the tracks. That's 75 cents a ride, ladies and gentlemen; 50 cents for kids. They call it "Trolley Extravaganza."

That's the Vienna car there, that red, white and black one, a 1910 model that pulls a 1909 trailer. Inside is wood, real hardwood, maple and oak, not aluminum and polystyrene and polyester and so many poly-things you can't even pronounce. The seats are wood slats: You didn't write "Dick and Mary Ellen Forever" with magic marker on them. And look, the windows even open.

The cabin was heated by the engine on cold days. People who stood on the platforms at either end froze, and the conductor-no fool he- closed the sliding doors and collected fares through a slot from the warm inside.

The gray one with the white trim bound for Neureuter Strasse is a 1924 Berlin trolley. In front, the glass lamp lights up. Inside the windows are shaded with red and white parlor curtains to which little white balls cling along the fringe. Standing passengers stay standing with a grip of bent wood on a leather strap. Smart shoppers shopped at Schoepf, "das Modehaus fuer die Familie" (the fashion house for the family).

In all, Germany and Austria donated five cars to the museum. The members shipped them to the States for $17,000. The fittings are brass, the lights bell-shaped and the deck roof lined with transom windows. The cars smell of attics and old trunks with surprises inside and a step on a button rings the bell.

In 1966, four years after trolley service in Washington headed for the great car barn in the sky, the museum acquired its first cars. As the country went gaga in the grips of temporary insanity, sending electric clean trolleys to the torch in favor of gas-gulping, smoke-spewing buses, A. E. Savage did what he could to stash a few out of harm's way.

Savage, a barrel of a man with gray hair cut short and country in his voice, retired from Metro three years ago after 38 years in Washington public transportation. Savage was vice president of D.C. Transit during the aftermath of Congress' decision to chop the trolleys up for scrap. It was his sleight-of-hand that saved what few cars remain.

"When you're vice president, you can do a lot of things," he says. He hid the cars in the Navy Yard Car House at 8th and M Streets SE; then he moved them to the Eastern Car House at 15th and East Capitol.

The museum has two sweepers that kept tracks clean with giant rotating bamboo brushes: One is believed to be the only car left that used to run on the Northern Virginia lines. And museum members hope to turn an 1898 Washington trolley into a "Gay '90s" car.

Camille's favorite is No. 1053, a D.C. Transit car made in 1935 by the now defunct St. Louis Car Co. It's one of the famed Presidents Conference Cars (PCC) that served Washington to the end and still carries passengers in Cleveland. Camille sits in the rear as the turquoise-and-cream streamliner clanks jauntily by goldenrod and witches' needles, wild cherry and mulberry trees, into the siding called Sycamore.

Sycamore, explains museum treasurer Ed Frazier, a retired school teacher, was the name of a stop on the old Cabin John line.

At one time you could board a trolley in front of Union Station and ride it through the Potomac Palisades to Cabin John. It was one of many connections: Rockville with Mount Vernon, Great Falls with Congress Heights, Laurel with Vienna and Washington with Annapolis and Baltimore. In the system's prime, there were few places in Washington you couldn't go on a trolley. For many, trolleys were the best way to get to the places they wanted to go most.

The first service began during the Civil War with horse-drawn rail cars that connected all four sections of the city. In 1888, cable cars took to the streets. They moved at a brisk nine miles per hour and the fare was five cents. Or so says Leroy O. King, Jr, in his book, "100 Years of Capital Traction."

Until the turn of the century, cable lines stretched from 15th Street west to 35th Street, and from Park Road south to Maine Avenue. Congress mandated that electrification for trolleys be underground in the City of Washington. This proved a problem: When the plows that gripped the electric line hit a snag, they disengaged, backing up traffic for blocks.

Open-air cars coursed Pennsylvania Avenue, Georgetown and the streets surrounding the Capitol. On hot days, Washingtonians leaned from the sides, catching cool breezes on the run to Chevy Chase Lake. On Memorial Days, the Marine Band played as it rode the trolley to the lake, to a seashell bandstand where the new electric lights danced in the night.

Electric lines began to spread into what was then the surrounding countryside, spurring development throughout Maryland and Virginia. In 1913 the Washington and Great Falls Railway and Power Company began operation between Bethesda and Great Falls to develop land around Congressional Country Club, for instance.

The Georgetown and Tenallytown Railway Company rambled up High Street and Tenallytown Road (later Wisconsin Avenue) to connect with the Glen Echo Railroad. At one point the track dissected a dairy barn: Cows studied passing cars from either side.

There was a time when you didn't need a tank of gas and three hours' driving to Williamsburg to ride the rollercoaster. For years trolleys carried Washingtonians to Friday nights of amusement at Glen Echo Park. The park was filled with music and lights and rides and the trolley stood ready to pick you up at evening's end.

The only remnant of all this is Tenley Circle, named after Charles Tenley who thought Tenallytown, from an earlier resident named Sarah Tenally, an abomination and had the post office change it.

Trolleys pulled mail cars up and down Pennsylvania Avenue. It's said that one of them picked up an unusual passenger westbound of a summer's afternoon in front of the White House. He had the right train, but the wrong car, the mail clerk said. Then he recognized President Theodore Roosevelt, who was meeting his children after school for a walk along the towpath.

Already by the 1920s, however, streetcars were losing ground to automobiles. Trolleys began sinking into the red and later, one by one, were bought by holding companies fronting for automobile and tire manufacturers. The Washington and Great Falls Railway fell in 1921, the East Washington in 1923 and the Bladensburg line in 1925. Mergers finished off the rest.

By 1933, all trolley lines in the city were under one management, the Capital Transit Company. In 1935 the last Washington-Annapolis- Baltimore train left the station. Buses were taking over trolley routes at a steady pace when Congress, in a fit of anger after a strike in 1955, ordered the company's charter revoked and the system converted entirely.

The new D.C. Transit abandoned the tracks to Rosslyn, which, with the turn-about station on the Virginia side of Key Bridge, once made something of the circle that is now tall weeds, trash and mud puddles. The North Capitol and Maryland lines took their last breath in 1958; the Cabin John, Tenleytown/Pennsylvania Avenue, and Seventh/Georgia Avenue lines in 1960.

Finally, on Jan. 28, 1962, the last holdouts, the 14th Street and U Street lines, cranked around the bend and out of sight for good.

Or was it? At least one group, the nonprofit Georgetown & Foggy Bottom Trolley Co., wants to bring streetcars back with four lines connecting Dupont Circle and Foggy Bottom with Georgetown. The Department of Transportation has agreed to give $250,000 to study the project.

It's almost just the same to trolley lovers such as Ed Frazier and Bob Cutting, retired postal service worker, and Jan Lantz, registered nurse, who wear the tall blue caps of the motorman. In the city you rode trolleys to work and sometimes to play. But out here, where cars and cares stay behind in the parking lot, you ride them to fantasies.

"They may come back," says Frazier, no regret in his voice. "That would be fine." :THIS WAY TO THE TROLLEYS

The museum, at 1313 Bonifant Road, is about a half-mile east of Layhill Road north of Wheaton. From Georgia Avenue, take Bel Pre Road east to Layhill, where it changes to Bonifant. Phone: 384- 9797. Sorry, there is no trolley service to the trolley museum.