Three-year-old Stephanie Rendon's world is dark and muffled, but she and other deaf-blind children are getting some help they need to reach out and take the risks that lead to learning.

Stephanie already speaks a few words, signs about 15, is slowly learning how to walk and is being toilet trained - all major accomplishments for a child born without any hearing or sight, whose bright mind is difficult to reach.Most with handicaps like hers remain helpless, passive individuals, unable to do anything but express the most basic needs.

"It is difficult to teach profoundly deaf-blind children communication and language, so they function far below their potential and usually as a retarded individual," said Cathee M. Christensen, a San Diego State University associate professor of communicative disorders.

Christensen runs an experimental program aimed at finding out how to motivate deaf-blind children to learn. The U.S. Education Department, which is spending $286,000 for two years on the program, serves about 5,520 deaf-blind children and young adults, said program specialist Charles Freeman.

The Helen Keller National Center in New York estimates there are between 30,000 and 40,000 deaf and blind adults in the United States, said Freeman.

A deaf-blind person's success in education depends on intelligence, quality of education, level of parents' involvement, whether training began at an early age and if they have any residual hearing or sight, he said.

"These children don't have concepts. They come to school without knowing what a square is, or a ball. . . . But before you teach them the concept of the mirror, you must establish some kind of common link. Once you establish that, you can start their education."

With a student-teacher ratio of 1-3, Christensen's program allows more personal attention than is normal in programs for handicapped children.

Much of the time is spent in a laboratory classroom, where teachers use such devices as a hand-held microphone that vibrates to sound waves, or puzzles made of various textured pieces. New teaching devices also are being developed through the college's electrical and computer engineering department.

Parents participate during the twice-weekly instruction, and staff members make regular home visits. Therapy sessions are videotaped, and the children's oral and physical communication signs are analyzed.