My great-grandfather was but a water-man, looking one way and rowing another.

John Bunyan, Pilgrim's Progress

THIS SATURDAY the Potomac will be speckled with an expected 350 watermen, all competing by advancing backward. The occasion is the seventh Scullers' Head of the Potomac Regatta, which draws sweep rowers as well as scullers.

The 20 races, which will run from 9 to about 4, are a thrill for rowers because they attract quite a few former Olympic scullers. They also present quite a spectacle for those on shore, with hundreds of racing shells scooting along the river like waterbugs.

Stuart Law (Yale 1950) has been sweep rowing (in which the oarsmen each use one oar on alternate sides of the boat) and sculling (in which an oarsman, singly or with others, uses two oars) for 40 years. Law, who will be sculling in his fourth Head of the Potomac race, explains that advancing backward, beyond the philosophical implications, presents real problems.

"Steering is important in a race," Law says. "I have to use a rear-view mirror, but I'm good at steering because of it. The other scullers don't use them." Law attaches his mirror to a headband. Not only do the scullers have to watch out for other boats on the course, they are required to pass buoys placed to prevent corner-cutting.

Sweep rowers are spared the hassle of steering because they are accompanied by a coxswain, a small person who steers and acts as a sort of cheerleader.

Washington scullers and rowers have enjoyed a new visibility recently due to the completion of Washington Harbour, which has brought tenants and visitors to the river. Nancy de Booy, promotion director for the waterfront complex, says that when showing prospective tenants around, she always has to stop if a sculler or rowing team rows past.

"The rowers who row in the morning provide a marvelous sight," she says. "It is a peaceful and graceful thing to watch. We have sponsored some races on the Potomac and one can really see a race close-up from here."

Participants return the appreciation. It is a beautiful thing to the rowers, who are required to keep their eyes in the boat, to hear spectators. Says Liza Draper, a coxswain for 11 years: "The more noise coming from the banks -- even unintelligible noise -- the better, especially during Head races." The Head races, held in the fall, are over longer courses than the spring sprints. "They can be grueling for the rowers," she says.

Law agrees. "But," he says, "you say to yourself 'nobody ever ever ever quits.' "

Among the more than 250 boats expected this year will be one "stroked" by perhaps the youngest sculler yet to compete in this race, 11-year-old Matthew Borchelt. He explains his motivation for getting through a three-mile head race with fifth-grade directness: "I like it. It's fun." Matthew's father, Mark Borchelt, taught him how to scull last year, and Matthew is proud to point out that, when the two of them practice in their double, it is he who strokes, or sets the pace. Contemplating this weekend's big race, Matthew says, "I get a little bit scared, but . . . my Dad said when he started, he always got scared."

Despite the regatta's emphasis on scullers, it has attracted many college teams that row in eight-oared shells. Navy coach Rick Clothier says: "We've been paying more and more attention to that race, ever since they added the sweep events a few years ago. That changed the nature of the race, making it much more than just a scullers' regatta. It is a very attractive and well-run regatta and a good one for us to row in."

The sponsoring Potomac Boat Club hopes the regatta may someday reach the size and status of Boston's Head of the Charles Regatta, the largest annual rowing event in the country. Can the Head of the Potomac be measured against the Henley Regatta, held on the Thames and attended by the likes of Lady Di?

"No," says Draper, "we're a little bush compared to the Henley. No stylish hats, for instance. Not a good round of Mr. Pimm's to be had. But most people come {to the Potomac} with their blankets and their picnics and have a good time."

Boats will be launched from PBC and Thompson Boat Center, flanking Washington Harbour and its boardwalk. "The boardwalk will provide a unique vantage point for spectators and allow greater numbers to watch the races this year," says Cindy Cole, chairwoman of the regatta and PBC's women's coach. This year's course starts just below Fletcher's Boat House, passes the Three Sisters Islands, goes under Key Bridge, runs between Roosevelt Island and Washington Harbour and past the Thompson and the Kennedy centers to the finish at Roosevelt Bridge.

Hilary Hess, who has helped organize the regatta, says the areas in and around the two boat houses from which boats will be launched will be open to the public. The college eights and fours will use Thompson, and it's always fun for fans to take a close look at the various racing shells, which display delicate worksmanship, lying in slings before a race. These shells are a far cry from rowboats. The seats are on wheels set on tracks, the hulls are thin and fragile, and the gunwales support boards to which the rowers tie their feet before rowing.

An easy wander from Thompson, on Water Street, is the Potomac Boat Club. Established in 1869, the club is housed in a quaint (if slightly musty) building. Photographs grace the walls along the staircase and in the large second-floor ballroom. These photos, depicting rowers with handlebar mustaches and a now unrecognizable riverbank, date from the 1880s, according to club member Donald Gilmore. PBC also boasts balcony and rooftop areas that give fans a bird's-eye view of the racecourse, a view often put to excellent use by photographers. WHERE THE BUOYS ARE

Good public spots for watching the Head of the Potomac Regatta:

WASHINGTON HARBOUR --

30th and K NW. The boardwalk gets you closer than any other dry-land vantage point, and offers benches, fountains and restaurants.

ROOSEVELT ISLAND --

The north end of the island and its eastern shoreline (although heavily overhung by vegetation). Parking's in the lot off northbound George Washington Parkway is limited, so get there early (or walk from the Rosslyn Metro).

THE GRASSY KNOLL --

Downstream from Thompson Boat Center at 30th and Virginia is a popular picnic spot. Don't try to park at Thompson; park along Virginia Avenue or in the Watergate or Kennedy Center garages. Or walk from the Foggy Bottom Metro.

RIVERSIDE PATHWAY --

The paved path that runs downriver from Rock Creek Parkway offers vantage points along the closing stretch and for the finish at Roosevelt Bridge, but you probably wouldn't want to spend the whole day there.