BILL HENRION KNOWS the exact day that doctors took his voice away. "July 1, 1987," he recites, as if it were a date he had memorized in school, one of those dates that signify a monumental change in the course of human events.

For Henrion, it was the beginning of a new kind of life. From that day on Henrion would be, in a sense, speechless; no longer able to take for granted what most of us assume will be our right - the ability to chatter, yell, whisper, laugh out loud. The ability to say what's on our mind, or just hum a little tune.But like other patients who have their larynges removed in order to stop the spread of cancer, Henrion has found a new voice.

"New Voices," in fact, is the name of a support group for laryngectomees - those who've had such operations - that meets the first Tuesday of every month at the American Cancer Society, 610 E. South Temple.

It's a meeting with plenty enough noise - because, although the surgical removal of the larynx means that the "voice box" is gone, there are several successful alternatives to bring laryngectomees out of silence.

Normally, voice is created when we exhale air through our closed vocal cords, creating a vibration that causes sound. Laryngectomees have to create that vibration some other way - either by vibrating the esophagus or by using an external vibrating device held up to the neck.

Henrion, for example, speaks by means of a voice prosthesis, a small plastic tube that carries air from his lungs, via the trachea, to his esophagus, which then becomes a substitute vocal muscle.

Like the vast majority of laryngectomees, Henrion was a cigarette smoker, puffing about two packs a day for 35 years. There are other contributing factors that lead to cancer of the larynx, including the consumption of hard liquor, especially when the drinking is combined with smoking. Most laryngectomees are usually big talkers, too, says Heather Dove, speech pathologist at the University Hospital ENT clinic and a professional adviser to New Voices.

But smoking is still considered the leading cause, as Marshall Adams is eager to point out when he speaks before school groups. Adams was a two-pack-a-day man for 50 years. Seven years ago he developed a sore throat that turned out to be cancer. When his doctor ordered immediate removal of his larynx Adams did not hesitate, even though it meant a future without his natural voice.

"I wanted to be alive," he explains.

Now 73, Adams is president of New Voices. He conducts the meetings the same way he converses with his wife, Mary - with an artificial larynx. The device looks like a small microphone and sounds like an electric razor. When Adams turns it on with his thumb it creates a humming sound. When he holds it up to the front of his neck, the vibrations travel through the neck to the throat, where he shapes the sounds by mouthing words.

Because the noise produced by the artificial larynx is always the same pitch, the speech it creates sounds like something from a robotic toy - a fact that fascinates small children and sometimes causes people to hang up when he calls them on the phone.

Laryngectomees who use artificial larynges generally develop a sense of humor about all this. Bill Henrion, who used an artificial larynx before he was fitted for his voice prosthesis, remembers standing in the check-out line at the grocery store one day, listening to one of those automated, talking cash registers.

"Hamburger, $1.98," said the cash register in its robot voice as the clerk slid a package of meat across the scanner.

"Correction, hamburger $1.19," said Henrion in his robot voice.

With his voice prosthesis he no longer sounds like a computer, but his voice does have a raspy quality that he says causes people to "look at me like I was the Godfather." He is able to get quite a bit of inflection into his voice, although he says he still has trouble with subtle shadings such as sarcasm.

Because his prosthesis connects his trachea to his esophagus, Henrion is able to use the large volume of air in his lungs to help create speech. Another alternative form of speaking for laryngectomees - esophageal speech without a prosthesis - uses air trapped in the mouth.

The advantage of esophageal speech is that it requires no external device or any additional surgery. The disadvantage is that it is difficult to master.

Tillie Davis, past president of New Voices, has been using esophageal speech since her operation in 1982. She has learned to trap air in her mouth, force it down her throat, trap it just below the esophageal muscle, and then release it back through the muscle. She must use air trapped in her mouth because her esophagus is not connected to her lungs.

A widow who lives alone, Davis has few opportunities to talk during the course of a normal day. So when she returned home from the hospital after her operation six years ago she practiced her new voice by talking to the radio.

"There are times when people lose patience with me," says Davis, who must take a breath after every 10 or 12 syllables.

But she is able to get along just fine, and like Henrion and Adams she is eager to let new laryngectomees know that the loss of a voice box does not mean the loss of a voice.

As Mary Adams says of her husband, "Marshall loves to talk."