A WHOLE GENERATION has grown up that doesn't know about trains, and every weekend now the Blue Ridge Line of Amtrak is hauling a fresh load of neophytes up to Harpers Ferry, introducing them to this old/new mode of travel. It's not exactly like shuffling off to Buffalo on the Twentieth Century or the Super Chief, but it's riding the rails. And two cars full of passengers every Saturday and Sunday are discovering there's romance in trains and getting there is half the fun.

All sorts of people are riding the Blue Ridge these days, and few of them have more than a nodding acquaintance with railroads. Weekdays, of course, it's different. A thousand commuters a day us the Blue Ridge Monday through Friday, standing in the aisles, reading their papers and taking it all for granted. But weekends it's a party all the way, with another railroad buff born every time the engineer blows that lonesome whistle on the curve. They're mostly families, with a sprinkling of backpackers planning to walk the Appalachian trail. To many, it's adventure. "We're explorer types," says Jay Levy of Garrett Park, Md., loading up his family of five for the trip to Harpers Ferry.

It's not really cheap for a family -- $7.50 round trip, half price for the kids -- but it's easy. The Blue Ridge leaves Union Station on weekends at the civilized hour of 10 a.m. and chuffs through the countryside to Harpers Ferry in an hour and a quarter. The crew, who on our trip were all B&O veterans, love their train and are never too busy to stop and talk to the kids, inquire where the family plans to eat, or recommend a point of interest. The roadbed is a bit rough but talking over old times with Bert Miskell, a conductor for 35 years, or Dale Shaffner, 25 years a trainman, makes this truly a trip back into the past.

If you go on the Blue Ridge, you will have four and a quarter hours in Harpers Ferry before they pick you up again. There's plenty to fill the time, but bring your walking shoes -- old ones. It takes a lot of walking to explore the 19th century in Harpers Ferry.

The town is a period piece at the confluence of the mighty Shenandoah and Potomac Rivers. It was once called Shenandoah Falls at Mr. Harper's Ferry, since Robert Harper, a prominent citizen, operated a ferry there in 1747. Fifty years later it became a federal armory which was destroyed during the Civil War when the town was taken and retaken repeatedly. In 1859 John Brown, the abolitionist, tried fruitlessly here to establish a separatist black state.

Most of the town is now under the protection of Harpers Ferry National Historical Park, administered by the National Park Service, which has secured pleasant, fresh-faced young people to play the role of shopkeepers and militia. There's a gentle conspiracy among them to pretend the year is 1864.

"Do you know who's president of the country?" inquires the young man in the uniform of a Union Civil War sergeant looking sternly at the small boy in the recruiting station.

"Carter?" hazards the boy.

"Carter?" repeats the sergeant in properly outraged tones. "You sound like a southerner. Abraham Lincoln is head of the Union."

It's all in fun, part of the play acting and restoration of this town carved from land belonging to three states. Stick around and you'll learn that the 34th Massachusetts Volunteer Infantry pays its recruits $16 monthly and takes just about anybody who is between 18 and 45 and has an upper and lower tooth that meet so they can bite the paper off the ammunition cartridges. You'll learn that desertion is a problem, and that it's lonesome to be a recruit away from home.

Every weekend through September -- and longer if funds are available -- park employees will be standing in for the 19th-century shopkeepers. You can watch a blacksmith sweating over his forge or listen to a young southern apologist putting the case for slavery to a crowd of idlers in the park. In the general store a top-hatted man stands behind the counter where once James McGraw, dressed exactly that way, sold whisky, horseshoe nails, coffee, horse muzzles, bee smokers and peanut roasters. You can walk though an old time confectionary shop and peek into the apothecary's office. Or flatten your nose against a Civil War dress shop.

The visitors' center, moved to the river side of Shenandoah Street because of a recent fire, will help you plan your walking tour or tell you how to join guided walks. But Harpers Ferry is essentially three streets and with a map provided by the center, you can find what you want by yourself. Check with the center if you go after Labor Day to see if the tours are still on. Tour directors sometimes tell you things you would never find out any other way. We stumbled onto a tour for children at John Brown's fort and heard the guide tell the group that the fort was dismantled and shipped, brick by brick, to the Chicago World's Fair, where exactly 11 persons were interested enough to pay 50 cents to go inside.

Our train conductor had advised us to be sure to lunch at Hilltop House and we followed his advice. We were happy with the choice, but it must be said we earned our lunch. Hilltop House sits a half mile above the town on steep, steep High Street and you will be puffing by the time you arrive at this old hotel, which was a favorite retreat of Woodrow Wilson and Mark Twain. The country buffet they lay out every Saturday and Sunday costs $6.95 for adults and $3.50 for children and includes ham, biscuits, cole slaw and everything you'd expect to go with it.

You can walk through the life of John Brown as created in a waxworks on the way back down High Street or you can get your picture taken by the Civil War photographer, posing in one of his selection of uniforms, bonnets and crinolines. But the real must is another climb -- "It's well graded," said a man encouragingly to us as we peered up the side hill where a flight of handhewn stone steps disappeared into the distance. This is the famous Jefferson's Rock and one of the treats of Harpers Ferry.

Jefferson visited here in 1783 and called the view "stupendous . . . worth a voyage across the Atlantic." In the fall, the banks of the river below will explode into color and the view will be even more dazzling. And afterwards, when you are through drinking it in, stop by on the way down at the house Robert Harper built around 1775. It's the house of an affluent gentleman of the period, spacious and comfortable, and he rented it to James McGraw for $60 annually.

At 3:30 the Blue Ridge comes huffing around the bend from Martinsburg and chugs to a stop on Potomac Street, just a spit from the center of town. As on an ocean voyage, you will have made friends and be able to compare notes.

And what did they like best?

"Why the train, of course."