On the idea of unisex, androgyny, or whatever the philosophical catchword is at the moment, Pierr Mornell has one answer. It starts with a "b" and ends with a "t," so you won't read it here. But it gives you some idea about how the California psychotherapist feels about blurring the sexes.

"Men and women -- after the obvious differences -- are two different animals. Period," he adds. "They cannot totally unite. Most husbands and wives have needs at night which are 180 degrees opposite each other's.

"The most important part of the man's day -- earning a living -- is over when he hits the front door. The most important part of a woman's day -- making a connection in the relationship -- is still to come."

This applies, he says, whether or not a woman works. "Women have more energy at night. They can work as hard or harder than their husbands, regroup, and then what they want to do is check in on their husbands."

What a man wants to do is tune out, says Mornell. With Monday-night football, the newspaper, anything to avoid what is going through his head as "talk, talk, talk. " (While the woman is thinking: "If only he'd talk to me. ")

According to one study, cited by Mornell, an average married couple talks with each other only 20 minutes per week.

The woman, says Mornell, sees her husband energized for work, and collapsed on the couch at home. "He's charming and on for everything and everybody else except her. The result is rage. She becomes bitchy; he reacts to it and withdraws even more, and they're off to the races.

"No wonder things break down after several years of marriage, especially in the bedroom. Talk is absoutely essential to women."

After seeing what he calls "an epidemic" of this syndrome in Marin County (where there's one divorce for every marriage), Mornell labeled it "Passive Men, Wild Women" and wrote a book with that title (Simon and Schuster, 184 pages, $8.95).

Although loosely-written and repetitive, it has struck a cord among women. "Men," says Mornell, "are too passive to pick it up."

He admits that there is nothing new or startling about his findings -- "I was just the one who bothered to put them down (by getting up at 2 a.m. daily to write)" -- and he's somewhat amazed at the response.

"I've had a lot of women tell me they were feeling like the Lone Ranger out there. 'You're talking about me,' they say, 'and you've never even met me.'"

In the past, says Mornell, 44, the assertive-female, passive-male pattern occurred later in life. Granny often became a dominating old lady while Grandpa sat back. He'd already proven himself with sword or plough.

"A man's greater muscular strength," write Mornell, "defended him against a woman's greater emotional strength."

But today, as he points out to no one's surprise, male and female roles are changing rapidly. The woman may be economically independent. There are probably not so many children to consume her time. She wants a more active husband and a lively relationship, the "something more."

"Passive men withdraw." ("Premature emasculation" is what one of Mornell's clients calls it.) "Wild women attack."

Men, says Mornell, always have been afraid of women. He quotes liberally from literature to support that point. For example: "A woman's tongue is only 3 inches long, but it can kill a man 6 feet high" (Japanese proverb).

"At some intuitive level," say Mornell, "men have always feared that women could dominate and destroy them."

A sigh from the doctor, who is also the husband of a psychotherapist and the father of three: "Men know that women are better than they are emotionally."

Talking about women's ambivalence in their independence and dependency needs, Mornell almost whispers, "I've heard feminists say, 'I'd like someone to be dependent on.'"

The way out of what Mornell sees as an escalating impasse?

"There's simply no shortcut. The man must be more active at home if his wife is to be less depressed.She, in turn, must begin to relax." Also, says Mornell:

Both men and women must admit and recognize their mutual needs for privacy. ("Women typically seek privacy in a locked bathroom" and "Both men and women are jogging, I'm convinced, not only to relieve stress, but for privacy.")

Women could learn to say "Let's not talk" more often, in deference to the man's more natural inclination for silence.

Set a time limit on talk, like a half-hour. It can help a man feel more in control, if he knows it will not be an "endless conversation."

Dump marital animosities every day -- "Like the trash, they accumulate."

"It is not a question," he says, "of how a husband and wife can be equal and alike . . . It is a problem of how a couple can be equal and different."