According to the forecast, the temperature could hit 75 today, which makes it hard to think normal, late-November thoughts of deer hunting, early skiing or hiking the frosty woods.

Indian summer like this sends my mind meandering instead to the river and prospects of a last fishing trip. Evidently I'm not alone. Trout Unlimited's National Capital chapter was looking for a big crowd last night for a talk by Bill Anderson of Falling Waters, W.Va., who pioneered cold-water smallmouth flyfishing techniques on the upper Potomac.

Anderson is among a growing cadre of area anglers that regards the weeks between Thanksgiving and New Year's as prime time to catch trophy-size bass. Indeed, Anderson's largest smallmouth, 5 pounds 9 ounces, came on Dec. 29, 1984, near Hancock, Md., on a day when he and his partner fished six hours and felt just three strikes.

"You don't get a lot of action this time of year," said Anderson, a federal communications specialist when he isn't fishing, "but what you get is generally quality stuff.

"The fish basically go up in size as the water temperature drops," he said. "At about 50 degrees, the little ones quit feeding. At about 45, the 12- to 15-inchers turn off. And when it gets down to 42 degrees, it's mostly two-pounders and up."

Anderson is not alone in that assessment. In his information-packed paperback, "Fishing the Upper Potomac River," veteran smallmouth guide Ken Penrod writes, "Winter, and in particular December, is the best time of all to catch trophy bass from the Potomac River."

And guide Mark Kovach, who runs fishermen downriver from Harper's Ferry to Brunswick all summer, said now is "definitely the time for big bass. In the summer, we may catch over 100 fish in a day, but we don't get many big ones."

With Potomac temperatures hovering in the upper 40s, trophy season is just around the bend. But even on summery days like this, it's no picnic out there.

Smallmouth enthusiasts favor the fast-flowing Potomac waters from above Great Falls upstream to Williamsport, Md., and like the river best after a good rain, when the water is two feet or so above normal. These are hazardous conditions even in warm weather, which makes it so worrisome in winter that Penrod admits, "I have problems when it comes to advising you to go fishing."

The experts want the water high because it narrows down the places where big fish lurk. "It forces them into pocket waters along the shore," said Anderson. "They want the maximum advantage of the current bringing them groceries, but they don't want to waste their energy fighting the current.

"In nature, if you spend more calories chasing food than you get consuming it, you starve to death."

The pocket waters that December's jumbo smallmouth favor are the eddies behind such river obstructions as points of land jutting off shore or boulders in midstream.

"The idea is to bring your lure along the eddy break, where the fast current meets the slack water behind the obstruction," said Anderson. "This is where the big fish go to feed."

Penrod says a hard-core angler might run 30 miles in a day, hopscotching from eddy to eddy in a boat powered by an outboard with a special, jet contraption on the lower unit. The jet replaces the standard propeller, which would be eaten alive by the upper Potomac's rocks.

Once at a proven eddy, the lure everyone agrees on is the Jig 'n' Pig -- a black, quarter-ounce, deer-hair jig with a No. 101 Uncle Josh pork rind behind it -- fished as slowly as possible along the bottom.

"These fish are feeding on one thing -- crayfish," said Anderson, "so you have to hop the bait slowly along into little holes," the way a crayfish would do.

"The key thing is to slow down," said Kovach. "You fish at about one-third the speed you do in the summertime. Just crank it along the bottom and have patience, because the fish aren't going to move very far to get it."

"They won't move a quarter-inch," said veteran Potomac fly fisherman Dick Blalock, "but if you drop it right between their eyes, they might pick it up."

Sound difficult? Anderson likes it even harder, using sinking-tip, lead-core fly line and huge, fuzzy, weighted rabbit-hair flies instead of spinning tackle and the Jig 'n' Pig. A strike on tackle like that, he said, practically requires ESP to be detected.

Which makes the whole business sound so complicated, I might just go hiking after all.

Penrod's 233-page "Fishing the Upper Potomac River" is a treasure trove of information and makes a fine Christmas gift for a freshwater angler. It's $23.95 from PPC Publications, 13028 Ingleside Dr., Beltsville, Md. 20705.