On the day before Thanksgiving, beneath a sun-splashed sky, Jack Scanlon stood knee deep in a cold trout stream and gave thanks for the fish that had worked so hard to hook itself on his lure.

"It's amazing how colorful these brown trout look when you pull them out," said Scanlon, returning his 10-inch catch to the Patuxent River's Cabin Branch. "Because underwater they are just so hard to see."

In this season of gratitude, it is customary to offer thanks for health and happiness, family, friends and flush bank accounts. Heaping portions of turkey and pumpkin pie head the B list. If you've still got some appreciation to spare, you might allow yourself a moment to reflect on what a fine and charming fellow you turned out to be.

Jack Scanlon, a Washington pediatrician and father of five, has all those reasons to be thankful this Thanksgiving. And a few more. Listen to Scanlon talk about the trout that are spawning now in his river and the deer and woodcock living by its shore, and you hear a benediction as heartfelt as any pilgrim's.

"With my job, sometimes things can get to you," said Scanlon, the director of neonatology -- the care of infants from birth to 28 days -- at Columbia Hospital for Women. "It's just nice to know that it's here. If I hadn't found this place, I'd have had to quit my job."

The fact that the Patuxent River is rich with reproducing trout, just 25 miles from downtown Washington, is due in part to Scanlon and his fellow members of Trout Unlimited. During the past decade, local chapters of the national conservation organization have volunteered time and labor to improve living conditions for the Patuxent trout. Last spring, the Potomac-Patuxent chapter spent $1,200 to buy hatchery-raised brown trout to stock in the special catch-and-release area of the river near Damascus.

Wednesday, Scanlon led a small party of trout lovers back to the Patuxent to see how those trout had fared. We were looking for spawning beds, known as redds. The female trout dig the beds with their tails and lay eggs that are covered with a layer of gravel after they have been fertilized by the males. This year, the evidence of nature's fecundity has been reassuring.

"It was an excellent year for spawning," said Charlie Gougeon of Maryland's Coldwater Fisheries Program, who met us beside the Patuxent. Adequate rainfall and moderate summer temperatures resulted in an above-average survival rate for the stocked and native trout. And that led to more spawning beds than normal for both the Patuxent and the Paint Branch, another suburban Maryland trout stream that supports reproducing trout.

And all of that means better fishing for those who think fooling trout is as noble an endeavor as an angler can undertake.

"Let's go down and see if we can find Moby Dick," said Scanlon, leading the way down a riverside trail to a pool where he caught, and released, a 24-inch brown trout this fall. He estimates it weighed more than four pounds.

"I had to wrestle with myself a little before I put that one back," conceded Scanlon. "But the trout is as much mine in the water as out. Besides, it will really be big by next year."

Guarding the rear of our group was Dick Blalock, a retired State Department official who received an award this fall from the Mid-Atlantic council of TU for his work preserving and protecting the Paint Branch. Together, they had saved more trout than I would ever see.

This is an appropriate time to give thanks for groups such as Trout Unlimited. During the past four years, as a result of state and federal budget cuts, private conservation bodies -- Ducks Unlimited, the Izaak Walton League and American Rivers Conservation Council, to name just a few -- have been challenged to provide the money and leadership needed to fill the void.

Trout Unlimited, which is celebrating its 25th year in 1984, will spend $1.3 million this year on federal, state and local programs to enhance coldwater habitat for trout and salmon.

Walk down the banks of the Patuxent and you will see evidence of that effort. Rocks have been rolled into position to maximize current. Downed trees in the river have been chained to live ones on the bank to provide much-needed cover for fish.

"You know God must have favored the salmonoids (trout)," said Scanlon, as we stood in the water, fishing upstream. "Because he put them in such gorgeous places."