When Betty Duffy opened her Bethesda Art Gallery in 1975 she had the right ingredients for failure, or so some of her colleagues thought.

"Several of the art dealers came by and said, 'welcome to the art world, but you're really going out on a limb,'" recalled Duffy.

To open a shop in the suburbs was to go out on a limb. To specialize, as Duffy decided to do, in original American prints from the first half of the century was to saw off the limb behind her. That, at least, would have been the opinion of many in the art business.

"Much to my amazement I began to sell immediately," said Duffy, who had been told to expect to lose money for at least the first three years. "I was as surprised as anyone else."

But using her independence of judgement, Duffy found her own success formula. Where others had thought the suburban location a handicap, Duffy saw it as an advantage.

"I looked downtown, of course, the P Street area (a major location for galleries in the Washington area), but I discovered that a lot of people who bought art lived in this area," said Duffy. "And I do as well. It's darned convenient." Customers must agree because the majority come from the Bethesda, Chevy Chase and Potomac area.

The gallery's focus on the relatively unknown field of early 20th Century American prints also has proved to be an asset, according to Duffy. The realistic style of these works coincides with what Duffy views as a renewed interest in realism. People who are tired of the abstract art of the 1950s or big, poster-type color art are attracted to these small, black-and-white works with their fine workmanship, explained Duffy.

Realizing that the field may be new to many of her customers, Duffy encourages them to look around at the prints, read about them, get a feeling for what techniques and subjects interest them. She keeps a small library of books, many of them now out of print, which customers may consult for information on the prints and the various media, such as wood engraving, dry point, lithography and etching.

"I have a few customers who buy for investment but I don't encourage it because there's no way to really know," said Duffy. "My advice to people - a cliche, but still good - is buy what you like and trust your own response, not what the dealer or someone else says is good."

In its three years of existence, the Bethesda Art Gallery has presented works from some of the major figures in American printmaking during the earlier part of the century, such as Howard Cook, George Bellows, Martin Lewis, Louis Lozowick and John Sloan. Although their names were famous in the 1930s and 1940s, many of the artists dropped into obscurity when realism went out of fashion after World War II.

Duffy's own interest in these works did not develop until the 1960s. Originally from Okalahoma, she studied art in Paris in the late 1940s and discovered that she had, in her words, "a lot of interest and not a heck of a lot of talent." When she switched to collecting, she primarly bought European prints. She began investigating American printmaking 15 years ago when she bought an etching by the American artist John Taylor Arms.

"I began to see how marvelous this work was and to realize how undiscovered it was," said Duffy. Once she decided to open a gallery, she said, "There was never any doubt in my mind what kind of gallery it would be."

Those artists who are still etching have, of course, welcomed the chance to be seen again by the public. The 78-year-old Howard Cook, whose show two years ago at the gallery was a sellout, wrote Duffy from his New Mexico home, "Thank you for bringing me back to life." Duffy will present another Cook show in mid-October.

Prices in the gallery range from $25 to $2,500. Duffy said most of her sales are in the $100 to $500 category, except for her Christmas show, which features prints for $100 and less. All the prints are matted in the gallery with acid-free rag mat, which avoids the "foxing" or brown spotting caused by matting with cresent board.

The current show, entitled "Outstanding American Prints," runs through July. The gallery, at 7950 Norfolk Ave., Bethesda, is open Tuesday-Saturday from 11 a.m. to 5 p.m. It will be closed during August.