Some guys hang out in bars. Others play golf. Then there are those whose idea of a good time is to stand around the railroad tracks just to watch the trains go by. In Prince George's County, the tracks they mostly stand around are in Riverdale.

They are guys like Ron White, retired from the Department of the Army, though he's got another part-time job working security at the Shrine of the Immaculate Conception in Northeast Washington--when he's not watching trains.

"Since I've been doing it, I don't have any more blood pressure problems," said White, 64, of Hyattsville, who started coming to Riverdale three or four years ago. "I find it very relaxing. Some people say a train whistle keeps them awake. It puts me to sleep."

White is one of a coterie of trackside pals who show up regularly at the Riverdale depot with their hand-held scanners tuned to the train frequencies, their cameras and their unbridled enthusiasm for the passing freights.

They often stop first at the Riverdale Bookshop and Coffee Depot, a used-book store with photographs of trains on the wall. Then they gather trackside. There have been up to 15 at one time, but mostly it's the same handful.

They are a small but close-knit fraternity who meet one another nowhere else, talk trains while they wait for them, then wave at the trainmen who pass by. The other day, they also worried about "Hubert," who was in Florida, and hoped that Jackie, another rail fan, soon would be re-employed.

But mostly they talked about trains, coming, going, backed up on some siding south of Baltimore, or heading north and then suddenly veering west just south of Riverdale. Even as they monitor the radio bands, they watch the track signal lights up and down the line, and they listen for the train whistles.

When they know a train is coming, and its direction, they hop from one side of the tracks to the other, to gain the best perspective. Then, resplendent in their railroad caps, they point and shoot and marvel.

"He's loaded!" Andrew Collins, 39, a food and beverage manager at a Great Falls country club, said as a train approached. "This is the Tropicana. . . . All juice in this area is brought up from the south on Tropicana cars."

The Riverdale station is a mile north of the "Y," a strategic rail junction where freights from the south can go north, past Riverdale, or west to Silver Spring and beyond. The Y is where the action is--35 to 40 scheduled CSX freights daily, plus 20 MARC commuter trains, according to Trains magazine--but it's also private property.

Nonetheless, there are legal vantage points at the Y, and some train watchers prefer them. Vince Cipriani, 42, an instructor for Prince George's Community College, catches the trains there two days a week between classes he gives in University Park and Brentwood.

Usually, Cipriani grabs a sandwich at Franklin's General Store & Delicatessen, on Route 1 in Hyattsville, then, camera in hand, runs outside when he hears a train coming.

"On Mondays and Thursdays, from 11:30 to 1 p.m., four go by," he said. "The 'Rockrunner' carries crushed stone to Bladensburg, and there are two or three piggyback trains carrying tractor-trailers on flatcars."

He also catches freights on the Pope's Creek line in Upper Marlboro and sometimes watches trains from Route 450 in Bowie, where the Pope's Creek line meets the Amtrak Northeast corridor tracks, and from the train platform at Laurel.

But, for the regulars, it's Riverdale, which also has ample free parking.

Often observing the scene with detachment is Ron Lang, 58, a retired car salesman, who stands in the station parking lot. "I see the trains, but I ain't that interested in them to see them twice," he said. "I live down the street. I'm out here almost every day. I usually come over just to kill time."

Not John Pennington, 78, retired from the District water department. He comes to see trains. "I usually try to come over here on Mondays," he said. He was joined by Collins, in a Chessie cap. "Here comes Andy," Pennington said. They greeted each other like old friends. Then came White. Then, finally, Jack Campbell.

Campbell, 44, grew up in nearby Hyattsville, where he watched the passing trains from his mother's porch. "Every day I'm here, sometimes at 9 a.m.," he said. "I love them. I love the trains--the colors, the models. And the railroad guys are my friends. You wave at them, they wave back at you."

The train watchers speak the trainmen's lingo. They talk of TOFCs (trailers on flat cars) and refer to such obscure track locations as Chesapeake Junction, Jones Hill and Tanglewood, places that exist on no road maps but are important reference points for the people who run the trains, which the train watchers refer to by their designated numbers, such as 175 and 173.

"This is probably 173, which is a piggyback," Collins said as a train approached from the north. "They don't race. They're fully loaded, and the top speed on that [subdivision] is 25. Here it's 79."

"The 175 is not far behind him," White said. Then came the horn blasts--long, long, short, long--and the TOFC, which had just a few cars. "He's not that long today," said White, disappointed. Quickly, the train was gone.

Listening to the radio chatter, they "pick up so much information," White said, including tidbits about the lives of the dispatchers who run the system by computer from Jacksonville, Fla. One of them, White said, "was going to quit and go out West, but they talked him out of it. There's nothing like these scanners."

Collins said, "We'd be dead without them."

"It's a love, that's what it is," White said of his train obsession. And therapy. "I hear a train whistle, any problem I have, if I have any, I feel fine."

"It's a way of life," added Collins, some of whose train photos are displayed inside the Riverdale station and who also designs model train layouts on the side. "It's hard to explain. It's just something in your blood, you know?" He averages three days a week at Riverdale.

Bells rang, and the railroad gate went down at the grade crossing. Another piggyback train came. "He's short, very short," Collins said. The scanner reported what the men knew firsthand, that the train was "getting clear of Riverdale."

"There he goes," Collins said. The train watchers waited patiently. They knew another would be coming, and then another. Repetitious, perhaps, but boring, never.

CAPTION: Ron White, left, John Pennington and Andrew Collins talk outside the MARC train stop in Riverdale.

CAPTION: John Pennington, left, Jackie Campbell and Ron White watch and wave as a train passes.