Success brings its own problems, Carol Fox will tell you. When the Lyric Opera of Chicago sells out its 3,570 seats for a performance, it costs Fox, the general manager, about $50,000 to $60,000.

It's not that Fox is complaining about the enthusiasm for opera in Chicago, where Lyric tickets are almost as tough to get as Redskins tickets in Washington. But every time Fox adds a new series, she has to go out and raise more money ($3.3 million last year) to make up for the budget deficit.

"Opera is by far the most expensive of the art forms," Fox was saying in what she describes as her husky "slightly bass" voice that was once a soprano. She testified on the Hill yesterday to urge congressmen to give more federal money for support of the arts endowment.

"The Lyric Opera gets about $185,000 from the endowment for a $6.7 million annual budget. The French give $25 to $30 million to one opera company. Here it is just $3 million for all our opera companies. At the Lyric, all we have to do is give costs us thousands."

She took a singer's deep breath and sighed. "I wish that i had had more time before the congressmen.It it so hard to be enthusiastic in five miniutes."

Back in the early 1950s, Fox, who then was a young slip of a soprano with no need to count carbohydrates as she does today, came back to her hometown after voice lessons in Italy to find Chicago, without a resident opera company. The memories of the glories of Mary Garden and pre-Depression opera were slipping into the past.

"I was young brash and very purposeful in those days," Fox recalls - and one one feels that not everything has changed since then.

With two other opera-lovers. Fox founded the Lyric opera, which has become one of the leading opera companies of the world. She makes it sound simple.

"I rented an opera hall and signed Maria Callas."

Those two facts are true but they leave out the bartering to rent an auditorium ("If they rented it for school graduation, why couldn't they for an opera performance?" Fox asked them), the flight to Milan and then on to Verona to pin down Callas, the money raised from father and friends.

Callas, then at the crest of her career, made her American debut at the Lyric Opera, singing Norma, Violetta, and Lucia. Young, brash and purposeful, Fox then pulled off the coup of the opera world - she presented Callas and Renta Tebaldi, then the two hottest voices of the opera stage, on alternating nights.

"I don't think that opera stars are as volatile as they once were. Just as the Junoesque figure and the soprano that touched stomach with the tenor also have passed," Fox said, not without a note of regret in her voice.

Perhaps she was recalling those nights at the Lyric when Callas the prima donna, would walk down the aisle, to upstage tebaldi in full flight of an aria.

"And, of course, she had to leave early or send the usher to retrive a pair of lost glasses. Personalities like Cailas and Tebaldi made opera exciting."

Fox, who is married and has an 18 year daughter studying paleontology at Smith College, now is being purposeful about a new project. In 1974, the Lyric Opera started the first American proffesional training school for young singers. There, singers takes classes in languages, movement, acting, fencing, ballet, and wigs and make-up.

"Most young singers would spend their money or another voice lesson instead of body movement study or dance. But sooner or later they are going to hve to do a minuet," says Fox.