"Time to practice" calls the voice of authority from the other room. "Do I have to? I'm busy," comes the reluctant answer.

Familiar" It's a common enough dialogue in many households, but this one has a difference. The voice of authority belongs to a 10-year-old, and reluctant practicer is his mother, trying once again to master the guitar.

Adults who never learned to play an instrument when they were children, had lessons but haven't played in years, or want to learn a different instrument, are signing up all around the area for classes in piano, guitar, organ, recorder, banjo and even the harmonica. Many prefer anonymity because, as a middle-aged Alexandria engineer put it, "I'm just doing this for myself. I don't want my friends to know about it, in case I can't do it well."

"There are now more adults than ever taking different kinds of music lessons," says Pat Tyrrell, supervisor of special services for Montgomery County's Recreation Department. "We used to offer only guitar classes, but in recent years we have scheduled classes in banjo, fiddling, dulcimer, recorder, harmonica, even tin whistle, and they all fill up every time."

"I'm practically tone-deaf," cheerfully remarks a 50-year-old housewife as she struggles to tune her guitar, "but I love making music. Well," she amends, "something like music."

"It's no easier now," groans a 40-year-old government economist as he tries to read the music, picking up where he left off years ago. "And the notes look littler to me, or maybe," he sighs, "it's my eyes."

Betty Shuey, a Rockville housewife and mother of five children ranging in age from 12 to 28, played the saxophone all her life -- "I took lessons from Les Brown's father on Les Brown's saxophone" -- and is now studying guitar. "Ive always loved folk music and the guitar is perfect. I sing and accompany myself on it. I think I was born way before my time. I like it back in the '50s before it became so popular."

The anonymous Alexandria engineer is studying piano because, "My son and daughter took lessons and sounded so good that I decided there must be talent in the family, and maybe they inherited it from me." A Bethesda man's reason for learning to play the guitar: I'm a boy Scout leader and I want to lead sing-alongs around the campfire."

Whatever their reasons, all of the would-be players are faced with the big, the most important, the most dreaded of all things . . . daily practice.

Some teachers say that teaching adults is a joy. "They are taking lessons because they really want to learn," says H.C. McMurtry, who sells pianos and organs at Campbell's music store in Tyson's Corner. "They are interested and motivated.

"But it is hard sometimes to get them to practice," admits piano teacher Fred Kafft of Alexandria. "Adults lead busy, hectic lives full of responsibilities and chores. If the lessons aren't interesting and challenging, and if they don't see progress, they might just give up and stop practicing. That's why I often start my adult students off by learning to chord with the left hand and play melody with the right. That way they are playing songs right away."

Jo Zukaz, who teaches folk guitar for the Montgomery County Recreation Department, encourages her students to practice "20 minutes a day every day, not one hour and a half before the lesson (a not-unusual adult device)."

"Ideally," she adds, "practice time will increase as the fingers get stronger."

Steve Hickman, who teaches fiddle at Glen Echo Park, says, "Some adults, if they have had lessons before, fall right back into the stereotype of saying, 'Oh this is too hard. I'll never learn to do it.'

"One reason the fiddle is so good foradults is that it is played by ear; it isn't necessary to learn to read music. I just hum a tune for my classes, or play it on the violin or doodle-ee-do it and the students, with lots of mistakes and wrong notes a first, try to reproduce it."

Hickman says it is hard to tell which students will make it and which will give up after a series of lessons.

"I had one guy who, after 10 lessons, was still trying to learn the material in Lesson Two. I thought . . . no way will this guy ever play the fiddle. Well, he dropped out for a while, came back and now he is doing great.

"I'm one of the people who, if I was in my class, I'd say would never make it. It took me months to get the basics. My father is a concert master and a director and he used to listen to me try to play and say things like, 'Give it up and learn a trade, you'll never make it. I decided that I'd learn to play just to show him that I could do it."

Adults take music lessons for many reasons, for relaxation, for a hobby or for a specific purpose. Guitar teacher Zukav has a lot of nursery school teachers. "They all seem to want to learn the guitar to play in their classes."

Stressing casualness and sociability, Zukav says, "We all sit around in a circle and strum and sing. If people are a little shy or timid about playing, a group is especially good because they get the practice without having to perform alone. They kind of blend right in with the group."

Guitar student Marge Turner of Rockville, who is in her early 40s and the mother of three, echoes for many the difficulty in finding time to practice.

"I usually wait until late at night when everyone is asleep and then I sneak downstairs and play and sing to myself."

"Playing an instrument is very satisfying," says piano teacher Kafft, "and if an adult really wants to learn there is no reason why he or she can't. All it takes is practice."

And then there's apt to be a different refrain from the 10-year-old in the other room.

"Mom," it goes, "can't you learn another song? You've played 'Who Put the Overalls in Mrs. Murphy's Chowder' 10 times already, and you always make the same mistakes."