WHEN SHE is not using her extraordinary soprano voice on stage, Helen Bickers may be found backstage painting scenery, sewing costumes or licking envelopes. "I've licked thousands of them," she says, "perhaps millions. Last year, when I wasn't cast in a role, I was wig mistress and worked on costumes. Frankly, there's more money in that, but I don't want to do it. What I want to do is sing."

This year, she is singing the title role in three performances of Puccini's one-act opera "Suor Angelica" for the Summer Opera Theatre Company, which does not really require its sopranos to lick envelopes but certainly won't tell them not to. "We need all the help we can get," says executive director Elaine Walter, who takes no salary for her work. "We have to stretch every penny."

In a city well supplied with small opera companies that try to work wonders on a shoestring budget, the Summer Opera occupies a special place. It operates at a time when all the other opera companies have closed down for the season. It was founded specifically to give experience and exposure to young Washington singers and will not cast a singer from outside the region in any role that it can fill satisfactorily with local talent. It pours all of its limited budget (about $50,000, which would hardly buy wigs for a Metropolitan production) into a single opera each year. This time, the company is doing two operas but only one show; besides "Suor Angelica," the program includes "Gianni Schicchi," also a one-acter by Puccini, his only comedy and perhaps his most perfect opera. Both operas share the same basic set and some members of the supporting cast.

Although the company emphasizes young Washington singers, the people who are brought together for this production span a broad spectrum of the operatic world. "I've sung 'Gianni Schicchi' hundreds of times, three different roles in it," says mezzo-soprano Shirley Thompson. "But this is the first time I've sung it in English. In rehearsal, the German words kept breaking through."

Thompson sums up her career as a singer in two sentences: "I went to Italy on a Fulbright in 1958. I went for one year and came back 16 years later."

After living and studying for three years in Rome (where she picked up some very expressive gestures she is now using in "Gianni Schicchi"), she went to Germany, auditioned and was immediately hired. In the career that followed, she gave about 900 performances in about 50 roles, beginning with a five-year engagement with the Heidelberg opera company.

"I was hired for 12 months a year to do nothing but sing opera," she says. "There was no way I could have done that in this country. There still isn't any way for a young American singer." Now, she is the head of the opera workshop at Towson State University and some of her colleagues in the Summer Opera are present or former students, still dreaming of their careers. "I have made my dreams come true," says Thompson, "but I had to go to Europe to do it."

American singers no longer have to go to Europe. Hundreds of small, regional opera companies like the Summer Opera have sprung up in America since Shirley Thompson went off to seek her fortune. They offer singers little financial security but lots of experience, training and exposure, and they have been helping to build a large audience for opera in this country.

Making a living is something else. Soprano Teresa Ann Reid sings with several local opera companies, has two degrees in music from Catholic University, has given private music lessons in her home, and will be a resident artist next season with the Connecticut Opera in Hartford. Still, she needs other work -- at the moment, work as a production assistant on the "Radio Smithsonian" program -- to supplement her income as a singer.

Tenor Philip Bologna, who has a leading role opposite her in "Gianni Schicchi," was winning amateur contests with "Santa Lucia" and Schubert's "Ave Maria" in his early teens, trained as a baritone at 16 and actually sang baritone roles in "Carmen" and "The Magic Flute" before beginning to work as a tenor. In the late '70s, he sang seven leading tenor roles with a small company in his home state, New Jersey. He has also sung with other companies, such as the Bel Canto Opera in New York, but he supports his wife and two children by working in a General Motors parts warehouse. His operatic activities have to be restricted to vacation or special leave.

For a production like the Summer Opera's Puccini double feature, that requires more than a month away from the job. Intensive rehearsals and coaching began in the last week of June and ran for three weeks, 12 hours a day, six days a week. The final performance will be a matinee next Sunday in the Hartke Theatre at Catholic University.

Fortunately, the tenor's employers were cooperative. "I told them that when I make it in opera I will do commercials for them," he says, but clearly his heart is not with General Motors and he has plans for a change of occupation. "My wife is a teacher," he says, "and for a few years she will be the main breadwinner. It's nice to have a wife who is behind you 100 percent."

Soprano Jung Ae Kim, who is alternating with Helen Bickers in the role of Suor Angelica, does not have Philip Bologna's financial worries. Since winning a Metropolitan Opera regional audition in 1977, she has had her training subsidized by the Met. She has lived in Washington since 1972 and sung with the National Symphony but has done most of her operatic work elsewhere -- including two tours with the touring company of the Houston Opera in "Madame Butterfly" and "Carmen." She probably does not need the kind of fringe benefits that attract other young singers to the Summer Opera, but she works with the company because, like Shirley Thompson, she feels that such companies are needed in America.

"The Summer Opera is like my home," she says. "I want to be part of it. If I become rich, I will support it with money. If they need my work, I will support them with my work."

Conductor Benton Hess began as a piano major at the New England Conservatory, "determined to take the scepter from Rubinstein," he says. "But I discovered that I didn't have the personality of a concert pianist, and being chained to a Steinway for eight or nine hours a day was not for me." aThe Conservatory cooperated; it instituted a major in accompanying for him. A career as accompanist for singers' recitals blossomed into a career as an operatic conductor. He has worked in the opera companies of Santa Fe and St. Paul, as well as the Lake George Summer Opera and the Goldovsky touring company. For six years, before deciding to free-lance as a conductor, he was the music director of the opera program at Boston University. "I have conducted 50 to 60 'Butterflies,' 'Toscas,' 'Bohemes' and 'Don Giovannis,' thanks to Boris Goldovsky," he says. "That's a kind of experience young conductors simply don't get."

Accepting the Summer Opera assignment meant turning down others that might be considered more prestigious."I came here," he says, "because I love the company, I love Washington and I love young singers."