Potomac River pilot Otis Kennedy Forbes had seen the blank look on the young lieutenant's face many times before, so he ignored it and sang out the course again.

"Come right to heading . . . " Forbes said calmly, repeating the new bearing and staring dead ahead into the cool, gray haze on the river.

The Potomac is that way: full of so many blind turns and creeks that end almost as suddenly as they begin that many an accomplished sailor has been fooled by the waterway. A merchant could have become a millionaire selling dead-end signs for Potomac tributaries.

There are, of course, no highway sign posts on the 75 miles of river from Smith Point on the lower Chesapeake Bay to Washington. The river's shipping channel, supposedly a minimum of 22 1/2 feet deep throughout its length, snakes back and forth across the often-wide expanse of water, marked only by small red, green and black buoys and triangular Day-Glo red channel markers.

Underneath the blue-gray waters lie the topsoils of West Virginia, Loudoun and Montgomery counties and elsewhere, forming massive sand bars that jut recklessly into the middle of the river and give employment to such men as Forbes.

Forbes, a tanned, silver-haired Ted Knight-look-alike from Newport News, and Bob Holland, a sleepy-eyed, middle-aged surfer from Virginia Beach, have come aboard this day to help get the Navy minesweeper Adroit from the Little Creek Naval Amphibious Base in Norfolk to the Washington Navy Yard. They are among the seven Virginians who hold licenses to pilot ships along the Potomac. Because the trip will take more than 14 hours, the Adroit is required to carry two of them up the Potomac.

Forbes, who at 57 has been on the river for 31 years and comes from six generations of Virginia pilots, can remember the Potomac's salad days, when he regularly would take two or three ships a week up or down the river. Today, thanks to interstate highways and the changing economics of ocean shipping, his Potomac voyages are less frequent.

With the exception of newsprint (headed for this newspaper's Alexandria warehouses), there are few bulk cargoes worth the cost of the slow, tedious transit up the Potomac. Shippers today want their merchantmen to be plying the high seas, quickly offloading and reloading in Norfolk and Baltimore--not meandering the Potomac.

For the Adroit, a 26-year-old, wooden-hulled minesweeper with a crew of 57, there are no shippers to please. She has been summoned to play a featured role in the Washington Navy Yard's Wednesday night summer ceremonies and so, for her and her crew, the trip is a mark of honor that will keep one of her sailors dabbing the ship's last gallon of "haze gray" paint to the ship's bridge as she chugs slowly up the Chesapeake and into a summer squall.

For Forbes and Holland, it is a routine they know so well that they come aboard only with a fresh change of clothes and a hand-held radio. Both men served six-year apprenticeships before they were allowed to seek their first pilot's license, and both spend most of their time piloting ships in and out of Hampton Roads at the southern end of the Chesapeake.

The work there is more profitable for them and the Virginia Pilots Association, the Norfolk-based group to which they belong. The association, which is paid a fee based on the draft of the ship, received only $168 for bringing the Adroit from Smith Point to Washington--a fee so small that a spokesman says the group "no doubt" lost money on the voyage.

Potomac River work is so scarce for the 90 members of the Baltimore-based Association of Maryland Pilots that only three of them remain qualified to bring ships to Washington. Those pilots often share the piloting duties with the Virginia pilots "just to keep their proficiency up," said Michael Watson, president of the Maryland pilots.

Still the pilots who recently sailed the Adroit were so familiar with the Potomac that, for them, the watertowers and other landmarks that the crew eagerly seeks along the riverbanks long have been etched in their minds.

The Potomac is a difficult mistress, they say. "Sometimes you may have to stay up 22 hours to make the transit, and you have to have the stewards to jab you to keep you awake," Forbes says. "You think you ought to go to the left and you go to the right."

At night it's worse. The pilots often literally have to be guided by the ship's floodlights. "You can't see anything at 2 a.m. Everybody's turned their lights off by then," he says.

This day, the Adroit's skipper, a New Jersey-born Irishman, Lt. Cmdr. Thomas J. Dougherty, welcomes the pilots aboard and tells them he is hoping for clear skies at night and a full moon. Forbes wishes otherwise. "The moon causes shadows, and shadows on the river can play tricks on you. I like dark nights."

Dougherty, who rose from the enlisted ranks and calls Baltimore his home, exercises his prerogative as commanding officer and tells the pilots that he'll let his crew take the conn (control of the ship) and "drive" the ship up the Chesapeake. Only when the Adroit enters the Potomac will the pilots take over.

That is not an unexpected routine on a Navy ship and Holland, knowing what is ahead once the river is reached, quickly goes below to grab a nap in one of the crew bunks. The voyage to Smith Point, at the mouth of the Potomac, is a slow one, with the Adroit making little more than 6 knots.

"Twelve hours out of Little Creek and we haven't got to Smith Point," Forbes grouses to himself as the ship, powered this day by only three of its four V-12 engines made by the old Packard motor company, begins to turn toward the west and the Potomac's mouth.

Dusk has begun to fall when Forbes turns to Dougherty and announces: "Captain, this is the worst place in the bay. More yachts have been swamped here than any other place in the bay."

"The Cape Hatteras of the bay?" asks Dougherty, sipping coffee out of a red, plastic University of Maryland mug.

Forbes, wearing an immaculate beige Izod windbreaker and a washable tan hat, nods. "You got the winds going one way and the current going another."

It is 2013 hours--8:13 p.m.--and the ship's log notes that pilot O.K. Forbes has the conn. For Forbes, the work has just begun and he lights one of many Vantage 100s cigarettes that he will chain-smoke until the Adroit docks. He walks to the port side to look for a light that will mark his turn up the river. "We'll go two miles up the channel and then we'll make our turn," he says.

He paces back and forth across the bridge, checking his own watch and taking bearings himself. A few minutes later, after one glance to the ship's port stern, Forbes gives the order: "Left 10 degrees rudder. Stay on course 305." The Adroit is entering the Potomac.

Forbes pauses and offers the crew a bit of history. Point Lookout, on the Maryland side, was the site of a Civil War prison camp, he notes. It is one of the many facts and sea stories that he will unravel throughout the night.

When the ship passes the Navy's Indian Head ordinance station the next morning, Forbes recalls passing the station when a large explosion went off. "Indian Head, Maryland," he says. "I always like to go by it in a hurry."

For Forbes and Holland, the only maneuver of the trip that seemed troublesome was timing their approach to the Woodrow Wilson Bridge. They were well aware of the controversies over the bridge's failure to close before a morning rush hour recently and wanted to time their arrival to hit the 9 a.m. opening.

Forbes had been confident that some of those problems lay with the Maryland State Police and their failure to close the bridge to highway traffic quickly. "Now, you call those Virginia police and they come just like that," he said, snapping his fingers in front of his face.

When he called the bridge from below the haze-shrouded river, he was assured the Wilson Bridge crew could, on its own, stop the traffic and get the ship through the span. "Shall we make this a one- or two-cushion shot?" joked Dougherty as the Adroit went to "all ahead full" to clear the bridge quickly.

Within 90 minutes the ship was moored at the Navy Yard and Forbes, who had disappeared into a stateroom to reappear in what seemed a freshly pressed suit, and Holland were scrambling over a rail and were the first ashore.

Forbes, a bachelor who had said he wasn't going to let "the grass grow under my feet," had a golf date back at his James River Country Club in Newport News and Holland had a tennis match in Virginia Beach. Potomac duty, it seems, isn't all arduous.

A Navy ship, like the Adroit, will be open for visiting every Wednesday night this summer at the Washington Navy Yard, from 7:30 to 10:30 p.m. For seats during the "summer ceremonies" pageant that features the Navy Band and Ceremonial Guard, call 433-2218. The show begins at 8:45 p.m. each Wednesday.