"When I use a word," said Humpty Dumpty in rather a scornful tone, "it means just what I choose it to mean --neither more nor less."

"The question is," said Alice, "whether you can make words mean so many things."

"The questins is," said Humpty Dumpty, "which is to be master -- that's all."

Most people have experienced conversations like that, say authors Julius and Barbara Fast.

"One person," says Barbara Fast, "is adept at manipulating words and dominates the conversation, and the other person becomes totally confused."

"Often the person gets confused because they are listening only to the literal meaning of the words," adds Julius Fast, "and ignoring the extra dimension of communication that is added to language when it is spoken."

That "extra dimension" is called metacommunication, write the Fasts in "Talking Between the Lines: How We Mean More Than We Say" (Pocket Books, $2.50). "It is a type of super-language," they say, "that comes from the meaning behind, within and around the words we use."

Elements such as resonance, pitch, stress, melody, dialect, accent and emotional overlay (like sarcasm or tenderness), they note, affect the meaning of spoken words. So it's not always what you say that counts, but the way you say it.

When the boss says "Are you feeling all right this week?" he or she, they claim, may really mean, "Your work is unsatisfactory."

"If you're sensititve to metacommunication," says Barbara Fast, "you can pick up the real underlying message."

"Metacommunication is to the spoken word what body language is to the body," says Julius Fast, whose book "Boby Language" is probably best known of the dozens they have authored separately and together.

The idea for a book on "supertalk," ("We didn't think of that title until after the book went to press") came from a melding of his "Body Language" book and her most recent, "Getting Close."

"Communication is an extremely important part of intimacy," she says. "Becoming sensitive to metacommunication helps you listen for what people are really saying and become able to speak more honestly yourself."

"The metacommunication message accounts for about 50 percent of the communication in spoken language," says Julius Fast. Commonly transmitted metacommunication messages include sexual attraction, superiority, insecurity and indifference.

"There's something about a French accent," notes Barbara Fast, "that often exudes romance and sex. Erotic messages can also be indicated by someone's choice of words or vocal inflection."

"Jargon in almost any profession," says Julius Fast, "can also send signals. Someone unfamiliar with the meaning of the words may feel inadequate, but may not realize that the speaker could be using jargon for just that purpose."

Metacommunication messages are often linked to a particular culture and can be misunderstood by someone from another, say the Fasts, pointing to their own experience in dealing with each other's family.

"I'm from the Midwest," she says, "and have always been taught that it's rude to speak loudly."

"But in my family it was accepted to speak loudly," says Julius. "With everyone crowded around it was the only way to be heard, and it meant you were part of the family. Since Barbara was quiet they felt she was aloof and disapproving. And her family thought I was a real pushy character."

"It took me a very long time to adjust," Barbara admits. "I have to keep reminding myself that the loud voices don't signify anger."

The only way, sometimes, to get to the root of the metacommunication message, says Julius, is to ask.

"Most people want to communicate effectively and be understood. If you think you hear an underlying message, discuss it.

"For example, take a couple who doesn't dig any deeper than the surface. She says she's perfectly willing to go to his mother's house for dinner. He picks up the distaste in her voice and says 'Don't do me any favors.'

"She can't understand why he's mad, because, after all, she said she was perfectly willing to go. So they split up, without really working out the problem."

A better way to approach this type of impasse, says Barbara Fast, is to pick up on the metacommunication message. "Say a husband comes home and the wife says 'The dog messed on the rug.'

"He picks up on the hostility in her voice and says, with genuine concern, 'You sound very upset about something, and I don't think it's about the rug.'

"This opens things up for her to say what she really meant -- but was afraid to say -- 'You bought the dog, I never wanted it.' Then, at least, they can work out the real issue."

Because metacommunication is emotional rather than intellectual, they say, "Much, if not all of it, is unconscious."