When he's working, Ted Watkin is always on a roll -- a high roll. His God-given 6 feet 7 inches stretch to a lanky seven feet when he dons his roller skates and becomes the latest twist to Washington's corps of couriers.

Watkin-on-skates makes most couriers who carry their cargo by bicycle, scooter or van seem, well, pedestrian. Since he began his job with Crown Courier Service six weeks ago, Watkin, who wears a purple shirt and yellow shorts, stands out in the crowd as he sways along the sidewalks of downtown Washington. Although he says he is not the only messenger who gets around town on roller skates, he is surely the tallest.

"This is probably the best job I ever had, this is fun," says Watkin, 27, who by night works at what he really loves--playing harmonica and sax in his rock and blues band called "All Points Bulletin." Roller skating is Watkin's way of paying his bills without having to get what he calls "a real job."

Roller skating is a fine way to travel, especially in Washington. "It's got everything a skater should want--a lot of nice surfaces, it's fairly flat, it's a good city for it," says Watkin, who was born in the District but grew up in Massachusetts.

Summertime though, has its hazards. The heat makes the pavement soft, "like molasses" and, as when a downhill skier hits a patch of slush, "it slows you down."

Watkin says his biggest problem is dehydration. "I'm usually drenched in sweat," he says. Which is why he prefers roller skating in winter. Other problems are minor: slippery grease spots and wet patches and vehicles that cut in front of him.

Though it is illegal to roller skate in D.C. streets, Watkin says no District police officer has yet bothered him. It is not always possible to stick to the sidewalks, he says, because of the people, cracks, grates and uneven surfaces. But Capitol Hill police take a more stern view of his mode of transport. Recently one stopped him as he was wending his way up the steps of the Capitol and threatened him with arrest if he did not take off his skates.

Bob Branam, who runs a skate shop on Capitol Hill, calls the ban on roller skaters "discriminatory," pointing out that jogging and bicycling are both okay on Capitol Hill grounds. It is also illegal to roller skate in any of the National Parks in the metropolitan area except in areas set aside for the sport.

Branam says he knows of about five other gliding messengers in the city and thinks there should be more because "it doesn't tie up traffic."

For the most part, Watkin rolls into buildings, rolls into the elevator--where he gets stares and comments (''nice legs'' or ''it's a long way to the ground'')--and then rolls down a corridor to deliver his package.

There are only a few buildings in town where he is ordered to take off his skates before he enters. "They are thinking that my skates are still the metal ones and will destroy the floors. But mine are hard rubber, they won't hurt them," he says.

They also are concerned about the possibility of getting sued if Watkin were to run into someone. "That's a valid point," he concedes, "but I'm not there to goof off, I'm in there to make deliveries. I probably have better balance than the ordinary person walking down the street."

Watkin's job has taken him all over the city and occasionally into Rosslyn. Downhill, he estimates his cruising speed at 30 miles an hour and "in a short haul" less than 10 blocks, "I would not be that far behind a car."

"What I'm doing is very unusual, so it definitely attracts a lot of attention; people can't help but see me," Watkin says, adding that he takes the stares in stride. And his best retort to negative vibes is: "Look, it's American, pal. Don't give me a hard time. It's energy efficient, it's an economical way to get around, plus I stay in great shape."

Mostly he feels like saying this to the businessmen who "just shake their heads" when they see him. "I figure they're all just jealous. They wish they were out there having fun," says Watkin, who has a college degree in history and a teacher's certification.

He doesn't have to worry about finding a parking space or locking a bike. And curbs don't present the problems they do for bikers. "I just jump."

He wears knee and wrist pads to protect him if he falls, which he says is not often. And if he does have to take off his skates to enter a building, it takes him about the same time as it takes a rider to lock up a bike--"about 45 seconds."

But Watkin does have "an incredible amount of maintenance work." He gets his skates cleaned once a week and sometimes his axles get bent or wheels need replacing. Last week "one of my wheels flew off." Left rear wheel, right skate.

"Physically it's pretty demanding; you have to be in really good shape," says Watkin, who weighs 200 pounds and has been roller skating for more than a year.

"It's much more strenuous than bicycling, but it's a lot more fun. You don't get as much distance for your calorie output, but I just have to give a few pushes and I can be going a few miles an hour.

"This is just a pretty wild job," he says. "I'll do it as long as I can but I can't see me doing this as career, full time. I have more ambitions than that."