Jeanette Gerald is fat. She is very fat: 5-foot-8, 270 pounds. She used to think of obesity only as a burden that made her feel unattractive. Then, six years ago, she learned how to use her weight to earn hundreds of dollars each week.

She and five other fat women crammed into a beige Buick, three in the front seat and three in the back, and drove from Anacostia to Philadelphia. There they visited scores of doctors, lumbered onto their scales, and drove away with prescriptions for the pink weight reduction pills called Preludin, an amphetemine sold to Washington's drug users to boost their highs from heroin.

A Washington drug dealer paid Gerald and the other women $25 for each prescription they obtained and had filled. The drug dealers also paid Gerald $5 for each fat woman she recruited for the scheme.

All the women lived in public housing around the 300 block of 51st Street NE, and had always been poor. But suddenly, as a result of the scheme, they were earning$200 to $1,500 a month. As far as they were concerned, it was fat city.

"It was beautiful money," sighed Gerald, 36, as she sat in her tiny apartment behind a coffee table littered with bags of potato chips, soda cans and crackers.

"I was able to give my children the best Christmas ever with lots of toys and clothes and everything. That made me very happy."

She bought new furniture with the rest of the money. But the furniture was stolen one weekend while she was away.

"I don't have anything to show for all those trips I made," Gerald sighed. Someone broke into my house and took everything. It was like they had a moving van. All they left has one chair. One plastic chair."

The man who paid Gerald and the other women for the prescriptions, Carl Lynch, was convicted last month on racketeering charges for organizing the scheme. Gerald and dozens of other fat women testified against him in U.S. District Court here in return for immunity from prosecution.

The women gave Lunch hundreds of Preludin pills each week between 1973 and 1976 - pills they had purchased for 8 to 14 cents apiece. Lynch had the pills sold for $4 to $12 each. Prosecutors alleged the scheme made him a millionaire.

City narcotics detectives believe that Lynch's scheme for getting Preludin to drug users in Washington is a common one - and that local fat women still travel to doctors in other cities, obtaining Preludin prescriptions.

Sometimes, they say, the schemes are less subtle: men and women visit doctors with financially shaky practices, make no pretense of wanting to lose weight, and offer large sums for Preludin prescriptions.

Drug users mix Preludin, heroin and water to boost the effect of mediocre heroin.

The fat women who helped bring Preludin to Washington's drug users have found their lives little changed from the days before they knew Lynch. They are still poor. They still live in public housing. They still spend their days watching over numerous children.

But now they share certain memories.

In the spring of 1973, Gerald was 30, unmarried and the mother of six children who lived with her in a tiny apartment in a public housing project in Anacostia. She had never worked, although she had dreams of traveling and becoming a singer.

One day, Gerald's next door neighbor asked her if she wanted to make some money.

"She told me that all I had to do was go to the doctor and get some Preludin pills for a friend of hers," Gerald later testified.

Gerald agreed to go. She needed the money and she was familiar with Preludin. Her own doctor had prescibed it for her to help her lose weight.

At first, Gerald's new job did not require out-of-town traveling. Once each week, Carl Lynch would drive to her home and take her and a half dozen other fat women to doctors throughout Washington. The doctors would weigh them, take their blood pressures, and give each a prescription for Preludin. Then Lynch would drive the women to pharmacies throughout Washington, where they would have their prescriptions filled, using money Lynch had given them.

But after several months, after the women had been giving each doctor several aliases, doctors in Washington became reluctant to give them Preludin prescriptions. Carl Lynch began driving the women to Philadelphia.

To Gerald, it seemed like the beginning of a new, exciting life.

"It was fun," she said. "I was getting away from the children for the first time. It was a chance to be free for a while."

They did not go sightseeing in Philadelphia. They checked into a Holiday Inn and began visiting doctors.

Their favorite was an elderly doctor. His hands shook and he did not see very well - or at least not well enough to realize that each woman, equipped with a wig and various aliases, was visiting him several times a day.

"Sometimes we would go in and see him one time," Gerald said, "and then we would go upstairs to the bathroom or go back to the car, maybe put on a wig or a pair of eyeglasses or something and go back in to see him again."

Then the doctor died, putting a dent in Lynch's business. Lynch decided to make an investment. He offered the women $5 for each new fat woman they recruited.

In the fall of 1973 Gerald recruited her neighbor, Sandra Fenkins, who is 5-foot-5 and weighed about 170 pounds. Jenkins was 16 at the time. She had just had a baby. Her boy-friend the baby's father, was "staying with another girl," and Jenkins wanted "to buy things for my baby."

The following summer Jenkins' mother, Juanita, recruited her son's 17-year-old girlfriend, who was 5-foot-3 and weighed 190.

Soon, there were carloads and carloads of fat women traveling to Philadelphia. When Lynch's cars had to be repaired, or there just weren't enough cars to go around, the women traveled by train.

Lynch always paid their travel and hotel expenses. The women had to pay for their own meals.

The women found doctors by driving in and out of Philadelphia's streets, looking for doctors' shingles.

After a while, they learned that certain doctors could be more helpful than others. "If you found a doctor in a shabby, office, you might ask him to write a prescription for a friend," Gerald said. "Or you might ask him to write prescriptions for a list of names. Sometimes the doctor himself would talk about finances, about it being hard to make money these days."

Not all the women enjoyed the travel. Sandra Jenkins said she would rather have been home with her baby, and besides she did not like Philadelphia.

"There were two many one-way street," she explained. "And when I'd go into a store I couldn't understand what they were saying."

Today Jenkins has her own apartment in a public housing project on Seventh Street SE. She has three children. She is not married. She is still overweight.

She says she is content: "All I ever wanted was a washer and a dryer and a home of my own," she said, sitting on an orange couch with a plastic cover. "As long as I can keep my clothes clean, my house clean, I'm happy."

Jeanette Gerald is less content. She said she feels as though she wasted her life, and talks of going to cosmetology school. She worries she will suffer some day for testifying against Lynch, and rarely goes outside her tiny apartment "expert when it's day light and there's a cab waiting right outside for me."

But she's happy she didn't go to jail.

Because the fat ladies sang. CAPTION: Illustration, no caption, by Aubrey Beardsley from "The Early Work"