There have been fish in the rankest parts of the Potomac River during the worst of times. Catfish, carp and crappie, the least-attractive sounding of all the so-called "trashfish," kept residence in the river when raw sewage drove away almost everything else.

But for genuine sport fish like black bass, the kind of fish that people travel hundreds of miles to catch in boats that cost more than $10,000 during tournaments that generate the yahoo atmosphere of a Texas rodeo, the Potomac during most of the last two decades ranked just a few notches higher than a drainage ditch.

So now comes the news, certified by one of the country's most popular outdoor magazines, that Washington, D.C., is bass country.

"When it's hot, the Potomac can be as good as any bass river in the East," says Pete Cissel, a Potomac River bass-fishing guide in a feature story this month in Sports Afield. "I've caught up to 40 bass in a day's fishing right here in Washington."

Cissel was on the Potomac again this week for a bass-fishing tournament that was designed to make friends of influential fishermen and show off the "Born Again Potomac." The one-day competition apparently did both.

"I always thought of the Potomac as a nice sewage dump for the city of Washington," said Dick Kotis, a nationally prominent bass fisherman who traveled to the Potomac competition from Ohio. "But this river is really nice. I'd like to spend a couple weeks here."

The "Challenge Cup" tournament is one of a dozen events organized by the Washington Area Waterfront Action Group this year to tout the renewed health of the Potomac. Some of those events, such as the seafood festival in August, will be aimed at a mass audience. The fishing tournament had a narrower focus--congressmen and high-ranking federal officials who control purse strings for waterfront funding.

"The congressmen finked out," said one disappointed tournament organizer after none of the congressmen invited showed. But the 14 bass boats that left the Maine Avenue waterfront at 8 a.m. had enough secretaries, assistant secretaries and under secretaries of federal agencies to form a bureaucratic navy.

The fishing was generally limited to the downtown stretch of the Potomac. While commuter traffic moved slowly along both sides of the river, the bass fishermen cruised past the Kennedy Center and the Watergate complex, casting for fish that some admitted they didn't expect to find.

But three hours later, when the brightly colored boats returned to the Gangplank pier, there were 31 bass aboard and some converted skeptics.

"The river has come a hell of a long way in just a very few years," said Ray Arnett, the assistant secretary for fish and wildlife at the Department of the Interior.

Arnett's boat returned with two bass that weighed in at more than two pounds each. Fortunately for Bill Gordon, the assistant administrator for fisheries with the Department of Commerce, Arnett didn't catch either of them.

"It's not the money, it's the damn humiliation," said Arnett, who handed over what looked like a $5 bill to Gordon, then explained to a reporter that it was Confederate money.

Although the quality of the Potomac has improved dramatically of late, its facilities for sport fishing are still primitive. There are only two ramp sites for car-top or trailered boats in the downtown area of the Potomac. And the best of those, near National Airport, is dangerous to use at low tide.

But the National Park Service last month announced that it is planning to build new boat ramps at Daingerfield Island, just below Alexandria. And both Thompson's Boat House and Columbia Island marina have recently begun selling a limited selection of bait.

Until now, local fishermen and a few professional guides have spoken loudest of the change in the Potomac. Cissel gave up a government job a few years ago to work the Potomac full-time as a guide. Ken Wilson is another full-time fishing guide. His cards read, "Come Catch a Bass in the Nation's Capital."

Cissel, Wilson and a dozen other bass fishermen volunteered their boats and expertise last week to take the feds fishing. Mike Birmingham of Dundalk, Md., who has traveled as far as Canada and Alabama to compete in tournaments, won a plaque for bringing back the most bass. Each of the nine fish was weighed, then released into the river.

"When I first saw the Potomac, in 1960, you couldn't have gotten me out here with dynamite," said Ken Penrod, a 40-year-old bass-fishing guide from Beltsville. "Now it's one of the really good places around here to fish. And we're not afraid to eat the fish that come out of here."