THE COSTUME workshop at the Folger Theatre is on the top floor of the sprawling but aged Capitol Hill building that serves as the company's home. Not too many years ago the floor was someone's apartment, and shadows of room partitions are still visible on the floor of what is now the large workroom.

In a small cubbyhole, where scraps of velvet and lace, sketches and photographs cover the walls, costume designer Bary Allen Odum sits at a drawing board that fills most of the room. Since he came to the theater four years ago, Odum has designed the costumes for everything from "Crossing the Niagara" to an Elizabethan "Julius Ceasar," to the current production of "She Stoops to Conquer."

While the staff of eight seamstresses and drapers labored in the sunny workroom, preparing for the first run-through, Odum explained why he and director Davey Marlin-Jones decided to model the costumes after fashions popular in 1680, rather than the era of the play, which opened in 1773.

"Davey wanted a sense of the earth and the soil, things that are important to Hardcastle, the things he feels are being eroded," Odum explained. "The clothes from the late 18th century, for women, tended to be light and bouncy, with big bustles and lighter colors. This period was heavier, more rococo."

Odum spent 20 years making costumes before he came to the Folger, and also taught the history of fashion at Brandeis University for eight years. It is clear that he relishes the research his job requires, and what may seem like pure confection to an audience is usually as historically accurate as he can manage.

The lighter colors of the late 1700s, for example, were influenced by the development of trade and the perfection of cotton, whereas in the period the costumes for "She Stoops" were drawn from, brocades and velvets were still the common fabrics for the monied classes. Odum's color palate for the play came from a striped tie that Marlin-Jones bought at Garfinckel's, "all browns and copper stripes."

As ridiculous as some of the fashion affectations seem to modern eyes, many of them had a reason for being. The high, vertical headdresses favored by women in the earlier era reflected their newly important role at court when William and Mary assumed the throne; with their layers of starched lace, the "caps" made women look extremely tall. And the multiple layers of corsets, petticoats, bustles, overskirts and jackets served not only as fashion but as insulation in the unheated homes as well.

Odum said there are only four examples of dresses from the period still extant, the most famous one a striped number in the Victoria and Albert Museum in London that every costume designer is familiar with. Two are in the Metropolitan Museum in New York. The main reason so few exist is that dresses were either handed down to servants or cut up and remade into children's clothes.

A lot of fashion was inspired by taxes or the ruler in power at the time," Odum said. "In the 16th century, for example, glass windows became fashionable. Then they began taxing them by the square inch, and so people sealed them up. The lace trade is another example; when the French wanted to increase the French lace industry they put taxes on imported lace. In another period buttons were taxed, so a fashion of having as many as three dozen buttons on one coat led to one of having no buttons at all. And men's wigs--prior to this period they got fuller because the king was aging and balding. Trousers were invented by George III because he got gout and his ankles were no longer pretty in knee breeches . . . "

Construction of the costumes differs from that of the original articles because they are "work clothes" and have to endure seven or eight performances a week that may include a variety of physical activities. The coats and dresses are specially lined for durability and protection against perspiration.

Most of the costume staff have specialties. Ric Rice, for example, is a draper with a graduate degree from Wayner State University. His job, after getting the costume sketch from Odum, is to design a pattern to produce the desired effect and then to cut the fabric. Coe Parkinson is the crafts artisan--she works in a separate alcove cluttered with baubles, bangles, beads, hat blocks, gewgaws and paint, and is responsible, in this show, for all the millinery, fans, jewelry, and gloves. "The ditsy work," she calls it. She is a graduate in costume design from New York University.

The two dozen costumes in "She Stoops" were made on a budget of less than $4,500. Odum bought the fabric in New York, where he knows where to go for the best deal.

"We tend to look at these clothes and say 'why bother?' " he said. "But don't forget, until World War II people really didn't have to get dressed by themselves. They had help. And the wealthy classes thought the more space they took up, the more respect they got. Until the late Victorian period, when it got to the point that they wore so much stuff they filled up the whole day putting it on and taking it off."