There was a time in Upper Marlboro when the Prince George's County Fair was a showcase for the fanciest swine and the fattest cows the county had to offer. From the fringes of the fair came the potent aroma of drying tobacco, and honey jars were stacked to the ceiling.

But it's a new kind of county now, and a new kind of fair. The few swine, sheep, goats and cattle loll inconspicuously behind the carney rides, while the central showcase of the air conditioned Bowie Race Course grandstand is filled with the elaborate gadgetry of city life.

The foot massagers have joined the king-sized melons on display. Now, among the first sights a visitor glimpses are a $13,500 Mercedes convertible and a group of home security system displays.

Rock and roll music blares from the neon-etched carney rides, and "Moonies" are on hand selling ginseng tea.

The farmers' interest in the fair has been lagging for years, as the farms that once covered the county are gobbled up by suburbs. But agricultural extension agent Dave Conrad is trying to lure the farmers back.

It isn't easy. Even the tractor dealers have to be begged to display their machines; they contend that they can't sell tractors to the new fair crowds. "We're 92 per cent urban," Conrad said.

This year's fair began Tuesday and ends Sunday at 10 p.m. The annual event began 30 years ago in Upper Marlboro, but moved to Bowie in 1975.

In this year's fair, the livestock entries were limited. None of the sheep producers live in Prince George's and only one of the country's eight swine farms bothered to bring the fattest and pinkest of his herd.

Fair manager Don Westcott is trying to offer a fair for everybody. While the state's Fair Board encourages the annual event for agricultural and livestock producers to meet in friendly competition and exhibit their products, Westcott said the only way to financial success is to attract "the urbanites."

So, when fair-goers arrive from the District, Seat Pleasant, Bowie and other urbanized regions of Prince George's Conrad and the agricultural producers attempt to teach them something about farming that can be applied to city life.

For example, "we can show them what kind of meat is in perfect condition and we can teach them to grow vegetables," Conrad said.

Entries in the gardening competition have increased over previous years, according to fair organizers. But now the watermelon-sized zuchini, prize-winning red tomatoes and butternut squash and other carefully cultivated vegetables come from suburban backyards.

The 4-H program has faced a similar problem convicing the public of the value an agriculturally oriented organization would have for youths growing up in the city and suburban areas.

"When people think of 4-H, they think of cows and cookin," said county 4-H agent Jody Wallace. "But a member can be a black kid in the suburbs studying electricity."

This year, 4-H members in Prince George's submitted a record 4,000 competitive entries, with projects ranging from the traditional canned and baked good to terrariums, hand-made pantsuits, miniature rocketry demonstrations and macrame.

As a testimony to the fascination animal breeding can have for possibly anyone, several youths clustered around rabbit judge W.J. Franklin as he used a quivering champagne-colored buck to point out why a firm loin, full head, sharp eyes and proper length ears combine to create a suitable commercial meat product.

"Let's face it," said Franklin, who is from Alexandria, "through this the also learn about qualit as a value," they learn "the facts of life the easy way. Now think about that."

All education aside, most people come to the fair for the same reason they always have - for fun. "I enjoy it," said Agnes Gianoly of Silver Spring who hadn't attended a fair in years.

There is the horse show today, and there will be a bicycle rodeo and helicopter rides. If Farrah Fawcett-Major is your obession, play "Skillball" in the carney games and win her poster picture.

It was simple fun that led Barbara Aremour a state unemployment office worker of Greenbett to the fair, and she wasn't let down. She's trying her skill at clowning. "This is my debut," she said with a giggle, behind a white and red grease paint face. "I was really down when I came, but I put on my face and felt wonderful."