Hear that whistle blow, boys, hear that whistle blow!

The Piedmont Limited pulled out of Salisbury, N.C., last Sunday and picked up steam, headed for Alexandria. Up front was the giant 610 locomotive, which in earlier days pulled the Texarkana-El Paso Night Express on the Texas and Pacific Railroad.

Aboard were some 900 passengers, most of them railfans, or friends, wives or children of railfans, taking advantage of a special run sponsored by the Old Dominion chapter of the National Railway Historical Society.

In the 610's cab, engineer W. A. Payne occasionally adjusted the big black and red throttle with both hands, while fireman Chuck Jensen kept watch on the gauges. Jensen brought up steam pressure to 225 pounds per square inch and kept it there. In no time at all, it seemed, the speed indicator read 50 mph. "That's a good safe speed for her," Payne shouted.

The old engine rocked and vibrated as it sped along the rails, venting pure white steam. Yellow fire could be seen in the firebox, fueled by oil from the tender.

As the Piedmont Special approached a road crossing, Payne reached up and grabbed the "cat's tail." The 610 responded with ear-spliting wails from the big whistle perched on top of the locomotive. Two longs, one short, and another long. People alongside the tracks waved happily.

"The steam locomotive," exulted Dick Page, president of the Old Dominion chapter, and one of the passengers Sunday, "is the greatest invention man has come up with."

Since the advent of the diesel, it is also an endangered species. The proud old 610, built in 1927, owes its existence to a wealthy Texan named Amon Carter - a railfan, of course - who several years ago found the engine unused and rusting away in a railyard. Carter invested a quarter of a million dollars in the "610 Foundation," which put it back in service again. In 1975 and '76 the 99-feet long locomotive pulled "The American Freedom Train" across Texas. More recently it has been used for special excursions on the Southern Railway lines. Sunday's trip included stops at Lynchburg, Monroe, Charlottsville, Orange, Culpeper and Manassas.

At Monroe, where the 610 took on fuel and water, an oil tanker stood on the tracks with a refueling crew. Monroe is an historic point on the Southern's main line. It was there, in 1903, that rookie engineer Joseph Broady began a run to Atlanta on the ill-fated "Old 97." Behind time and travelling too fast, 97 jumped the trestle at the foot of White Oak Mountain at Danville, Va. and crashed.

That kind of catastrophe rates at least a song, and in this case it was "The Wreck of the Old 97," a refrain that several on board the Piedmont Limited knew, and sung.

The passenger list included a few Washington-area railfans, like Peter R. Hefler of Arlington, an Air Force information officer, and Joe Drago of Manassas, who took his children - Tony, 6, and Tammy, 4 - along, too. Tony said he felt dizzy during the trip, "But I'd like to drive a train like this. Right up in the cab! Right up with the engineer." Mrs. Drago drove to Alexandria to meet them at the end of the 12-hour journey.

About 300 people were waiting when W.A. Payne guided the 610 into Alexandria's Union Station at 8:05 p.m., a little behind schedule. "There's nothing tough about driving this engine," he said. "Nothing tough about it. She runs pretty easy. She brings back memories for me."

The National Railway Historical Society has other trips planned this month for the 610. On Aug. 20, 21 and 27, there will be excursions from Alexandria to Monroe; ticket prices are $20 for adults, $18 for children 5 to 12 years old. The NRHS address is P.O. Box 456, Laurel, Md. 20810.