In the brightly lit basement of Bethesda Presbyterian Church, the arts have never been livelier than during this summer at a camp where the teen-age volunteers often have as much fun as the children they help.

Tanya Odarchenko, 15, of Potomac, grinned broadly as she talked about her summer with the elementary school-aged children. "One day in Motion Madness pantomime , the group had to pretend they were parts of a forest, and I was a stream," she said. Arms outstretched, she gestured briefly.

Tanya is one of a growing number of teen-agers working as volunteers this summer in a variety of Montgomery County jobs. Mary Costabile, assistant program director for the county's Volunteer Bureau, a clearinghouse, praised the youths: "People tend to criticize teen-agers a lot, and the criticism is not usually well-founded. The kinds of teen-agers volunteering have been generous, giving and interested in others."

Youths volunteer for jobs partly to test career options, she said. "We also believe that the current job market is a contributing factor," she said. "We are seeing lots of students this summer who say, 'I don't have a job, and that's why I'm volunteering.' "

According to the Gallup Poll, 52 percent of American adults and an almost equal proportion of teen-agers worked as volunteers between March 1980 and March 1981.

Costabile said her office does not keep figures on teen-ager volunteers but estimated that their numbers increased 10 percent during the 1981-82 school year, a trend that has continued this summer.

Working with art supplies and younger children at the arts day camp, held under the auspices of Round House Theatre, Odarchenko has learned some things she will use in the future. "Next time I baby-sit, when I'm tempted to turn on the TV, I'll look for scraps around the house instead," she said.

Thirteen-year-old volunteer Jeff Riebman of Silver Spring said his work at the camp is "a big responsibility, but I enjoy it."

At Banbury Cross Farm in Clarksburg, a group of learning-disabled children, ages 4 to 12, rushed into the tack room and hurriedly put on hard hats. They attend Riding for the Handicapped, a program founded on the belief that physically and mentally handicapped children can benefit from the challenge and discipline of learning to ride a horse.

Gael Cavanaugh, 16, of Libertytown in Frederick County, has volunteered at the farm since 1977. "I like working with horses and kids and when you put the two together, it's just the perfect combination," she said.

She recalled teaching riding to an autistic boy. It was difficult to get his attention, and she said she wondered if he ever really understood her. "One day," she said, her face beaming, "he began to post."

Learning to ride is an important accomplishment for a child who may not have much control over ordinary body functions. Cavanaugh said riding "gives the children a feeling of authority because they are on a big horse and can control it." One 7 1/2-year-old boy was content to leave such analysis to his volunteer. "That was fun," he squealed.

Judy McGaughan, director and riding instructor, said: "The learning-disabled children have a variety of problems. Some can't take instructions well. Others have motor control or speech problems, or delayed development." Because of the children's special needs, volunteers are used on a one-to-one basis.

In the riding arena, volunteers, holding the lead lines attached to each horse, walked around the arena while the children were asked to follow a number of directions, from circling one hand for balance and coordination to getting into the jump position. Volunteers who work with physically handicapped children act as "sidewalkers," holding onto leather and canvas body harnesses worn for added security.

Volunteer Angie Lepore, 14, of Monrovia, found she related well to the handicapped children. "I get a lot out of doing this," she said. "When they accomplish something and they smile, that makes me smile because I feel really good for them."

High school students, on the threshold of adulthood, often find volunteering can help them make career decisions. Last spring, Jess Borg, headmaster of St. Andrews Episcopal School in Bethesda, used the county volunteer bureau to find jobs for his seniors.

Shelly Donohoe of Bethesda, a senior who wanted to become an elementary school teacher, volunteered for the Head Start program, designed to prepare young children from poor homes for school. Donohoe said that as a result of her job, "I feel 100 percent sure that I want to go into education."

At Volunteers for the Visually Handicapped, Janet Montgomery of Bethesda, another senior at St. Andrews, learned to read Braille. She said she found "blind people are as independent, with proper initiative and training, as sighted people."

Her plans to become a doctor now are more solidly based. "It's important to get all the working experience you can . . . in a related field," she said.

Borg said his students had experiences "that are quite a bit unlike those you have in normal school life. They are real and they do give you a great sense of worth and accomplishment."