There was a time when the walnut bookshelves across from the bed in Mark Caplan's apartment held pictures of women -- frosted blonds like Joanne and bashful brunets like Chris.

Now there are photos of a red-and-white Western Maryland SD 40 freight engine where Chris used to be, a blue and yellow B&O F7 Diesel in place of Joanne. The girls have been stuffed in the T-shirt drawer. First things first, Caplan explains

"Too many women I meet think I'm going to put my love of trains in the back seat," says the 29-year-old Caplan, tan behind his Abe Lincoln beard. "It's not like I'm going to take them to the train tracks on every date, but there are some things a woman has to understand."

Two things, really -- trains and food. For Caplan, the two themes wind together like the starchy strands of leftover spaghetti and flagmen used to feed him when he rode the Western Maryland cabooses as a boy.

Caplan is a 10-year veteran Conrail towerman by trade, one of the last in a day when computers have taken over much of the railroad. A solitary worker in an antique brick tower overlooking Second Street and Virginia Avenue SW, Caplan spends his days throwing a few levers, making sure that the 40 or so trains that every day pass his station don't crash head-on.

Off hours, Caplan is a rail fan who has chased vintage trains 180,000 miles across country in the "Bionic Banana," his yellow 1971 Ford Maverick. mOften, when he can't sleep, he listens to some of his 7 1/2 hours of homemade train tapes on his stereo, bathing himself in the hiss chuga chuga chuga of a Chessie 614 or the Woooooooooooo of the five-chime horn on a Southern Cresent diesel as it barrels through the night toward home.

An old sign calls Caplan's railroad tower "The Gateway to the South" -- though it's about as memorable as passing Bucksnort, Tenn. on I-40 East on the way to Nashville. Licking the top off a chocolate fudge cupcake, Caplan stares down the rail line toward the Washington Monument, past the three sets of tracks and the thick, black 13,000-volt power lines, unused since spring when the old electric engiens were retired in Washington.

The Gateway was once home to the presidential trains of FRD and Harry S. Truman. Today, trains stop here only for emergencies. But if Mark Caplan wants to see a train up close he can look at the glossies he has mounted on the tower walls, some of the 6,000 he has in his personal collection.

The phone rings and Caplan picks it up, swallowing the last of his cupcake and leaning his chair back against the tool of his trade, a 41-lever Union Switching Signal Model 14, the original equipment supplied when the tower was built in 1911.

"Hi," says Caplan . . ."How's your appetite these days."

It is Jack, a former fellow bowling leaguer whom Caplan has converted to a rail fan.

"And Becky. How's her appetite? . . .She's picking strawberries? . . .Yea? . . .Are they big and ripe and red and juicy? . . .Super sweet, huh? . . .Makes her own jam? . . .Homemade strawberry shortcake, too? Well, save me a piece. I'll bet they're good on waffles.

"Hey, listen. . . ." Caplan is interrupted by a voice crackling over the intercom. Bob Young, the towerman in Conrail's other Washington tower in Anacostia, is calling.He alerts Caplan that an 89-car freighter is coming Caplan's way; it appears as a green light on the edge of the train routing board that hangs from the tower's 12-foot ceiling. Caplan pulls a few levers, then calls the dispatcher in Philadelphia to advise.

"Virginia South ENP7A, Down 3, 11:36. What'd ya eat for lunch, Joe?"

"Turkey with lettuce and tomato on white," Joe Eubanks says.

"Did my name come up at dinner?" Caplan asks.

"No," Joe says, as he usually does when Caplan asks. Not long ago, Caplan remembers, Joe got so tired of telling Caplan day after day that, no, his name hadn't come up at dinner that Joe suddenly cut loose at his dinner table:

"Mark Caplan Mark Caplan Mark Caplan Mark Caplan Mark Caplan! "

"What the hell are you saying?" Joe's wife asked.

"Let him ask me tomorrow if his name came up at dinner," Joe said.

Caplan was raised in Oxon Hill, the son of a supermarket manager who would drive his two sons to a hill overlooking the Florida Avenue tracks on Sundays. On holidays, the Caplans would go to grandmother's house in Chambersburg, Pa., a mile from the main line of the Western Maryland Railraod. Day after day, he would hike along the tracks, tightrope walking the rails, catching rides back and forth in the snorting red-and-white engines until dark.

"I was in heaven," Caplan recalls.

By the time he was 15, Caplan was saving the money he made bagging groceries at the supermarket during the week and taking the Capitol Limited to Harpers Ferry on weekends. The highlight was dinner in the dining car, usually roast young turkey with cranberry sauce, snowflake potatoes and rolls, all for $2.75.

"That was class," he says. "That was living. I knew the menu by heart."

Today, when he gets the chance, Caplan chases trains. His most recent adventure -- aside from his trip to Disney World and Fort Lauderdale, where he stayed in a Days Inn room overlooking the Seaboard Coastline tracks -- too him out west, where he rented a car and stalked the Rio Grande Zephyr, a proud, swollen-nosed diesel that is one of the last of its kind.

For two days, 700 miles and 216 pictures, Caplan chased the orange and black beauty, paralleling it on I-70 as it sped through red-walled canyons and sweet smelling aspen woods. At times he drove alongside it at 83 mph with his knees on the steering wheel, his hands pointing the camera out the window.

Other times, he would speed ahead to a scenic spot, jump out of the car, take a picture, and then tear off again to catch up. The Zephyr crew began "playing along," Caplan says. "At several scenic locations they slowed down to about 40 mph so I was able to prance across the tracks and snap away."

Caplan finally bowed out of the chase, waving his hands in thank you. Three long, low, sweet blasts from the three-chime horn came back.

Two days later, Caplan rode the Zephyr himself. The train undersay, he looked for a conductor who a friend had said could quietly supply a pilfered but authentic white-on-white embroidered Zephyr tablecoth, complete with the train's insignia. Here's how Caplan recalls that day.

"Hey," Caplan boomed to the red-suited young man when he saw him.

"Not so loud man, be cool," the conductor said, looking up and down the aisle and leaning down toward Caplan. "Now, maybe I can get you a tablecloth, too. How much did your friends say I charged you?"

"I think about $10 a piece," Caplan said.

The conductor thought a second. "I'll tell you what. For you, I'll make it two for $15. Put your suitcase on the seat and I'll bring them."

The conductor returned soon, the prized tablecloths bulging under his coat. The exchange made, he asked Caplan to join him for lunch.

In the dining car, Caplan took a fancy to the starched white coats with the gold braiding around the neck and lapels worn by the waiters who kept returning with course after course of his meal, Spanish omelet, home fries with onions, a side order of peas, tossed salad with Thousand Island dressing and freshly brewed iced tea.

"Boy," he said, "I'd really like to have one of those jackets."

"Are you serious?" the conductor asked.

"Size 42 long," Caplan said.

The conductor left and came back with the jacket. It cost Caplan $15 and added another to his collection, which includes a red Amtrak waiter's jacket and a blue Western Maryland Railroad windbreaker.

The conductor-cum-salesman pitched on, offering Caplan a sterling silver tea service for $20. To that, Caplan said no: There were no Zephyr markings on it.

That's Caplan. Valuable sterling bought cheaply doesn't mean anything to a man who knows what life is worth, knows the clickity click of steel against steel, the smell of diesel fuel in the air or the billowing black steam from a Chessie 614.

"I'm always hummin' when I come in to work and always hummin' when I leave," says Caplan, letting out a long, low blast from his lips, Wooooooooooooo: a precise imitation of the five-chime horn on a Southern Crescent diesel as it barrels through the night toward home.