Although William Gross loves the theater, he stopped buying tickets for himself about 10 years ago.

"I'd get my wife tickets, and she'd go with a friend," says the retired pharmacist, who has a 20 percent hearing loss in both ears. "It got too frustrating for me to go.

"Whenever the actor or actress would face away from me, I couldn't hear. I'd ask my wife to repeat what was said, but that got annoying -- for us and the people around us. So I stayed home."

Hearing impairment -- the most prevalent medical problem in the country -- "isolates you," says Gross, "from life."

"You don't see movies everyone's talking about, you get left out of conversations, you stop going to church or synagogue because you get so disgusted about not being able to hear.

"Someone starts talking to you at a party, and you don't respond so they walk away. I went to a big charity banquet awhile back and heard the comedian's jokes, but couldn't catch the punchlines. So now I contribute, but don't go to the banquet."

Since his retirement three years ago, Gross, 74, has focused his energies on getting "hearing-impaired people back in the mainstream of life," as a volunteer for the Washington Area Group for the Hard of Hearing (WAGHOG).

His hard work has begun to pay off.

"Our group had contacted area theaters about installing sound-amplification systems for the hearing-impaired. Last year the Kennedy Center invited me down for a test of their new infrared system.

"I put on the headset and walked around the whole Eisenhower Theater -- at the back of the auditorium, upstairs in the balcony. Everywhere I went, I could hear."

His response?

"It's hard to explain," he says, blinking back tears. "How do you explain seeing the sun come up after a bad storm? It was a thrill that comes to people only on very important occasions. I realized that, perhaps, I hadn't been wasting my time."

Since then, the National Theater and Arena Stage also have installed amplification systems for the hearing-impaired. When Gross took 42 hard-of-hearing people to see "Children of a Lesser God" at the National Theater, "They came out and kissed me.

"Most of them hadn't been to a show in maybe 5 to 15 years. I'd had to really urge them. Now they can't wait to go again."

Although attending the theater is one small step for a hard-of-hearing person, Gross considers it a giant one toward public awareness of the needs of hearing-impaired people.

"We're getting audio loops (amplification systems) in more and more places, like the Montgomery County Council chambers, the Smithsonian's Baird Auditorium, churches, synagogues. I just got a notice that the House and Senate chambers got an audio loop that will be ready for use in September.

"In New York several movie theaters have systems for the hearing-impaired that operate on an AM radio frequency. I'd love to see 'The Four Seasons.' Maybe I won't have to wait until it gets on TV." (He has a special amplification switch on his television set.)

Among WAGHOG's other projects: getting public telephones equipped with amplification switches, working with manufacturers to improve equipment for the hearing-impaired, lending a sample "audio loop" system to groups around the country and lobbying for a national hard-of-hearing symbol.

Although one person out of 14 has some hearing impairment, says Dr. Ralph Naunton of NIH's Communication Disorders Program, "many people are reluctant to seek help.

"Our society often equates hearing impairment with some sort of intellectual inadequacy. It's also associated with aging, and some people don't want to face that."

Environmental noise -- from jets, trucks, machinery, stereos and other loud sources -- he says, is resulting in increased incidence of hearing loss. Some people with minor impairment, "often aren't aware they have a problem.

"Children represent 20 percent of hearing-impaired people. It's not uncommon for some of those youngsters put in remedial classes to have a hearing loss as the root of their problem."

Helen Keller, notes Gross, once said that if she had the choice, she would rather be blind than deaf.

"Because the human voice is how you make contact with the world around you," he says. "When you're cut off from that . . . it can get lonely."