Dewey Marron stood beneath the gleaming bows of two $87,000 boats, trying to spot customers among the hull-thumpers slowly navigating their way across the concrete floor of the Washington Convention Center. Marron wore a dark coat, a brown tie and the look of a man holding a full house, kings high.

"You can feel it. There is a pent-up desire about ready to burst," said Marron, an owner of Atlantic Sailing Yachts in Annapolis and one of the exhibitors at this week's boat and recreational vehicle show at the downtown convention center.

"It's kind of like playing the slot machines. Sooner or later, you know the payoff has to come," he said.

If attendance is any indication, the folks who make their living by selling access to the great outdoors are doing very well here this week.

Since Saturday, when the doors to the new $99 million center opened for the nineday show, the 5 1/2-acre display floor has been crowded with pale pleasure seekers.

The timing of this show couldn't be much better.

After Washington's worst snowstorm in years, the chance to spend a few hours surrounded by summer's bright sailboats, cruisers and luxurious campers seems a welcome antidote to February cabin fever, even with the adult price of admission at $4.50.

"I think most people who enjoy boating get itchy about this time of year," said Ernie Chabot of Washington, who had just finished exploring the deck of an $8,379 boat that he had no intention of buying. "I'm just looking around, getting a feel for things."

Even without the blizzard, this year's boat show was expected to attract audiences with money to spend. Interest rates on loans dropped enough that buying a boat no longer means signing a lifetime contract with a bank.

In December 1980 the prime rate was 21 1/2 percent. By last December, the prime rate had dropped to 12 percent. The Boating News reported this month that boat shows across the country are having record sales.

At this week's show, half a dozen banks paid for display space to advertise loan programs for boat and recreational vehicle purchases. And people were lined up to discuss them.

"People are buying boats," said John Slattery, the sales manager for Tri-State Marine in Deale, Md., which opened in a converted gas station 18 years ago and now operates from a 10-acre lot and a 35-boat showroom.

"Even the snow didn't stop people from coming down last weekend. We weren't run over, mind you, but Saturday people were there."

Dave Pujals, a salesman with Safford Lincoln Mercury of Silver Spring, was holding court on the other side of the convention floor, showing campers to a crush of customers and looking pleased.

"The last few years, things have been very weak," said Pujals.

"It's getting better now, and you can write 'Thank God' beside that," he said.

Pujals was standing beside one of the most popular of the 400 recreational vehicles at the show, a front-wheel-drive Phasar motor home that is not much longer than a family station wagon and is said to get 22 miles per gallon from its diesel engine. The Phasar, made by Winnebago, was priced at $19,987.

The most popular boat at the show was a squat, metal-hulled, steam-powered freighter, and it was the only boat not for sale. The African Queen, the original tramp steamer used in the 1952 motion picture of that name starring Humphrey Bogart and Katharine Hepburn, was wedged like a rough jewel among the sleek fiberglass sloops, yachts and sunfish.

The Queen, now owned by Jim Hendricks, who uses it to advertise his Holiday Inn in Key Largo, Fla., was a working freighter in the swamps of Uganda and Kenya when John Huston bought it for the movie classic. After the movie was made, the Queen remained in Africa as a workboat until 1968, when a San Francisco restaurateur purchased it.

At the back of the convention hall, one display, in particular, seemed to brighten dispositions. Joe Czarniecki of the National Oceanic and Atmospheric Administration provided weather maps and a semiofficial, long-range forecast.

"We'll probably have an early spring," said Czarniecki.

The show will continue through Sunday. Weekday hours are 5 to 10 p.m., Saturday noon to 10 p.m. and Sunday noon to 8 p.m. Admission is $4.50 for adults and $2.50 for children 6 to 12; those under 6 are admitted free.