"Open up! Let's see the gold teeth!"

"That's flat! Fix it."

"Nice! Go on - I don't want to touch that."

With a mixture of charm, humor and musicianship director Sandra Willetts is preparing the Southern Maryland Choral Society for its opening concert this Sunday. The singers obviously are enjoying the good-natured cajoling of their conductor, whom they call "Sandy."

During the rehearsal, someone laughed at a comment. "What's wrong?" Willetts asks. "Are you enjoying this?"

Behind the quick wit is a thoroughly professional musician, who teaches music at St. Mary's College, knows the conductor's craft inside out, does structural analyses of scores and organizes rehearsal time like an efficiency expert. In Willett's view, it takes both knowledge and humanity to be a successful conductor.

A solid musical grounding is essential, she explained, "because you have to be able to play your instrument. The chorus is my instrument, and the rehearsal is my performance, not my practice session. If I prepare right, if I've done my practicing by myself - that is, learning the music, planning rehearsals to get the maximum done in the least amount of time."

The technique and knowledge must be tempered with warmth and psychology, said Willetts. "Group therapy - that's what choirs are. We're a big, happy family. We come together for a learning and spiritual experience.

"Conducting is such a responsibility. You're not dealing with an inanimate instrument. You're dealing with human lives and, more importantly, human souls."

As the conductor of a 100-voice chorus, Willetts is something of a rarity in the Washington area. Although women frequently conduct church choirs, leadership of large choral organizations is almost exclusively a male domain. Willetts, who has been leading the Southern Maryland Choral Society since 1975, sees a correlation with the general status of women in our society.

"The conductor is a figure of authority," she said. "It's only recently that women have been allowed to be in positions of authority, to go ahead rather than having to keep proving themselves."

In the past, women had to be far better than men even to be considered, said Willetts. "Now, I'd probably get the job because it would look good to get a woman as a conductor."

Willetts is hopeful that the future will bring a balance. "Then, if I get a job, I'll go back and practice some more."

Asked if a woman brought a special quality to conducting, perhaps a greater warmth, Willetts replied, "No. It's not the woman, it's the person . . . I feel good about conducting and good about being a woman, and I don't connect the two."

Included in the concert Sunday will be the premiere of a commissioned work, "Song to the Soul of a Child," by Washington area composer Winifred Hyson. The fact that Hyson is a woman was incidental to her selection for the program, said Willetts, who had heard and liked other works by the composer. Learning the rather complex music has been a growing experience for the chorus, said Willetts, adding, "Every season, I've tried to stretch them without breaking them."

Looking at this season, which includes Handel's "Messiah" in December and Mozart's "Requiem" in March, Willetts said that the choral society, based in the Clinton area, is "providing a real service to this corner of southern Maryland. We're presenting the major choral works that you can't get without going to the Kennedy Center - and I'm aiming for Kennedy Center quality."

Sunday's concert, which includes Leonard Bernstein's "Chichester Psalms," begins at 8 p.m. in the auditorium of Friendly Senior High School in Oxon Hill.

Asked if, as a conductor, she is aiming for the Kennedy Center, Willetts replied, "I may not get to perform in the Kennedy Center and maybe that's not important . . . If I can instill in my singers a certain progress of self confidence, I feel that's my greatest mission, above the music. Maybe I'll have changed their lives, and that's important."