An elderly woman wearing a floppy straw hat to shade her face from the sun stood before farmer Melvin Lewis' vegetable stand one recent Saturday morning and challenged him to prove that his "sweet yellow corn" really was.

Lewis, known for the freshness of his produce among regular shoppers at the D.C. Open-Air Farmer's Market at RFK Stadium, took the dare. He simply shucked an ear of corn and invited her to "taste it."

The customer, satisfied, not only bought a dozen ears for $1, but in a few minutes came back for six more.

This was one of the examples of personalized commerce often overheard at outdoor markets that draw Washington area shoppers to parking lots and sidewalks around town every summer weekend. Low prices, fresh produce and a chance to buy directly from people who grow the foodstuffs are some of the things customers said attract them to the markets.

"It beats Safeway, anyway," said Joe Lewis of Camp Springs, who said he is an every-other-Saturday shopper who comes to the RFK market because it is cheaper, more convenient and provides a better selection than do grocery stores.

Across town, an unshaded brick plaza in front of the Perpetual American Bank at 18th Street and Columbia Road NW comes alive on Saturdays with the colorful wares of farmers, gardeners and bakers, and with a clientele reflecting the rich ethnic mix of the Adams-Morgan community.

Perpetual American allows farmers and nonprofit organizations to sell their goods on the space rent-free if they present acceptable identification and sign an agreement.

Stands representing the Adams-Morgan Community Center; SED Center, a bilingual school for the poor, and Andromeda, a group that helps mentally and physically handicapped people, are a few of those that sell produce to benefit their respective groups.

Farmer David Dolittle of Lancaster, Pa., said he loads more than a ton of fruits and vegetables on his trucks and drive three hours to Washington on weekends to sell his wares.

"I come down here because there's more of a demand," Dolittle said. "There are so many farms in Lancaster that every house has its own garden."

The idea is to bring in fresh produce and raise money for programs for the organizations," said Francisco Nugent, branch manager for the bank. "Right now, we have five farmers on a regular basis and 10 to 15 nonprofit groups."

A newer market on an unused playground lot in Georgetown apparently has not captured that area's attention. A recent Saturday morning found six vendors doing a less-than-thriving business at the 34th Street and Wisconsin Avenue location.

"People who come here look but don't shop," said Jim Crawford, owner of a stand at the market, who said the operation has been disappointing since it opened in June.

The RFK market, which has been in operation for six years and sells fresh fruits, vegetables, seafood and flowers, was intended as a "direct marketing program from farmer to consumer," according to Eric Smith, a consultant for the market.

Generally considered one of the largest farmers markets in the country, with its estimated 10,000 to 15,000 shoppers a day, the stadium site teems with commerce on weekends as a melting pot of customers shops from vegetable stand to fruit stand pinching and picking the produce.

Customers found peaches at 49 cents a pound; apples, 59 cents a pound; $1 for a basket of six stubby green cucumbers; $1.25 for three pounds of string beans; $1.25 a dozen for brown or white eggs, and at least one item probably not sold at the corner grocers: six-ounce bottles of Josie's Mum-Bo barbecue sauce at $2.50 a bottle.

Farmer Lewis said he does not make enough money to justify all the work he puts into growing the freshest crops, but he "likes dealing with people straight."

Lewis said he commutes from Baltimore County, where he pours a lot of labor into growing corn, tomatoes, string beans, cabbage and greens, and he "always sells out" his stock for the day.

Consultant Smith, who assists the management of the D.C. Federation of Farmers and Consumers Markets Inc., said, "We try to put the markets in an area with low- to middle-income" people who need savings and nutritional analysis.

A doctor comes in every Tuesday and Thursday to counsel customers and farmers on how to cook and store foods for the best nutritional value, he said.

Unlike some of the larger markets, Eastern Market at North Carolina Avenue and Seventh Street SE takes on a different identity on Sundays.

The throngs appear as thick as the Saturday vegetable shoppers and include many middle- to upper-middle-class shoppers from the Capitol Hill area, there to buy antique furniture, jewelry and vintage clothes from flea market vendors who rent space for $15 to $25.

According to Russell and Tonya Berkley, who own The Vintage Shop, an antique shop, in Baltimore and go to Eastern Market on Sundays, the prices they charge there are "cheap compared to regular antique stores."

For example, an early 1900s breakfast set, with two original bentwood chairs and the table made from a sewing machine, was sold for $199. Also on sale was a waterfall dresser with an amber and clear toned mirror for $120.

Connee Stevenson of Silver Spring said she enjoys shopping at flea markets for "unusual, unique antiques" that she cannot find in stores.

Both flea market and farmers market shopping, Stevenson said, are "great fun and recreation [where] people can really save some money."