Freud clutched his black cigar between his teeth and gave a resounding "No," to the idea of children sleeping with their parents.

Doctors, psychologists and other professionals have echoed the idea that allowing a child in the parental bed is unhealthy. Not only because of the threat of deep psychological damage, but because mother or father could roll over on baby. Add to that the possibility intoned by at least one pediatrician: "If you let that child into your bed, he's not going to leave until he goes to college."

Some parents, of course, ignored the warnings and cuddled up with their offspring anyway (although they weren't likely to tell anyone except their closest friends). Others dutifully maintained a strict policy of separate beds.

Now, although the family bed is hardly a new notion--group sleeping of one kind or another was common until about 100 years ago--the taboo is lifting. In the wake of the human-sensitivity movement, communal sleeping, although still controversial, could become almost chic. "The Family Bed--At Last It's Okay" bannered a Parents magazine headline, to the relief of untold numbers of parents everywhere.

The woman most often credited with the family bed's current vogue is Minnesotan Tine Thevenin. Her book, The Family Bed--An Age-Old Concept in Child Rearing, is the bible of families in which children are welcome to sleep with their parents and when they leave the parental bed, share nocturnal accommodations with siblings. Advocates of this philosophy believe that the family that shares the same bed is healthier, happier and better adjusted than its counterparts.

Family Bed was written six years ago by Thevenin, wife of a Minneapolis Symphony Orchestra musician. Shared sleeping, she says, resolved the bedtime problems she had with her own two daughters, now teen-agers who have long since left the family bed. Unable to find a publisher, Thevenin borrowed money to print the paperback book herself. About 40,000 copies have been sold and it has been translated into two languages. British child authority Dr. Hugh Jolly gave the book an enthusiastic review in The Times of London.

"I've lent my copy to at least 16 people," says a 35-year-old Arlington mother of four who initiated co-family sleeping several years ago.

"I've gotten thousands of letters from all over the world in the last six years, supporting my ideas," says Thevenin. "Many say, 'Thank goodness I read your book and can finally come out in the open. Our family has been sleeping together for years.' "

Acknowledging that the practice is not for everyone, Thevenin says, "I want to encourage people to listen to their own feelings and give them support."

To her, the question is not how the idea of co-family sleeping started, but how we all got sidetracked in the first place.

"Throughout the world and since the beginning of time, families have slept together. The privacy phenomenon that moved children into separate beds and even separate rooms is only a hundred or so years old. And it smacks of affluence. The idea of sending a child off to a cold, dark room never occurred to the ancients, who only had one-room caves to begin with."

"When middle-class Americans think of masses of people in a bed, they immediately think of poor people," comments one devotee of the practice. "For much of the world, the question of where to sleep is moot--there are no options."

The-more-the-merrier-bed-chamber philosophy, proponents insist, is far from perverse. The habit is apt to be started by women who elect to nurse their newborn, and find taking the baby to bed both convenient and nurturing.

"I just didn't have the energy to get out of bed at night," admits one woman. "Having the baby there with us," says another, "just felt right."

Observes another, "It's unnatural to stick your children in separate rooms. Animals don't do that, they cuddle together. It would be like a fox sticking each of her babies behind a different tree."

But what does the open-door policy do to the sex lives of the parents?

"Most of the families who participate in the family bed have several children," pronounces Thevenin. "Obviously, they manage."

"I read lots of advice I did not agree with," says the Arlington mother. "I had a 4-year-old who was having tantrums. The books all tell you to walk away and ignore the child. Personally, I felt my son was pleading for help, and what he needed was more attention, not less."

After reading the Thevenin book, she decided to plunge into the family bed with their son and two daughters. Her husband, a 35-year-old postal worker, was not at all sure he wanted to tack a welcome sign on the connubial bed. He also thought dragging a second twin bed out of the attic so that the kids could sleep together was a pain.

He relented; they tied the twin beds together and united the mattresses with a king-size sheet. They took the baby into their bed and told the other children they were welcome, but let them share the twin beds. They now have another child, and the three older children claim the sibling bed. The new baby has never been in a crib or playpen in her life.

"It's an energy-saver in winter," says the father. "The three children all vie for the spot in the middle. Competition is so keen, we have to have a calendar that lists when each child gets the coveted location."

The parents feel their children are happier and closer. Their life, and especially the morning routine, is more peaceful, they say, and nightmares and bed-wetting no longer problems.

However, admits the mother, "Many people feel threatened when I talk about the idea."

Thevenin says the groups she lectures to are "overwhelmingly responsive" except for a chilly reception on the "Phil Donahue Show" several years ago.

"The majority of the audience," she says, "was middle-aged women who had already reared their children. They didn't seem to be open to new ideas. They were defensive, as if asking, 'What's wrong with what I did? I raised my children right!' "

What about plastic-covered feet in the mouth, wet beds, children who kick and toddlers who climb over exhausted parents? What about babies who have no civilized idea about the proper hours for sleeping?

Family-bed participants admit there are problems, but they tend to gloss over them and talk about the benefits: such things as the joy of watching a small child yawn and stretch in the morning, the fact that bedtime is not a problem, that the dark at the top of the stairs is no threat if you have someone to snuggle with.

If a child is particularly restless or more bodies crowd in than there is room for--there are limits--one father simply goes to bed in another room. "We play," he confesses, "a lot of musical beds in this family."

Esthetic arrangement of furniture is not apt to be a top priority. Some families squeeze two king-sized beds into a single room. Others throw out the frame and headboard and put all the mattresses on the floor. Some people build platform beds.

Beyond decor, standard parental guides warn that one of the grave dangers of inviting a child into your bed is that you are stuck with him for life.

"Not so," claims a 37-year-old mother of four boys, age 3 to 12, and the wife of an electrical engineer. "When the children are ready, they'll separate from you and ask to sleep by themselves or with other family members."

"Children walk when they are ready; they get toilet-trained when they are ready and they leave your bed when they are ready," says another woman.

The parents also believe that when a child needs privacy, he will ask for a bed or a room of his own, separate from siblings. "Listen," they say, "to the child."

And perhaps to yourself, as a 36-year-old writer sees it. His son, who spent the first three years of his life in the family bed, has now been in his own room for two years.

"I miss him. When he calls, it is now I who go to his room. And many is the night that I fall asleep there . . . it just seems very natural to us."