One of the most difficult questions a parent may face at this time of year will come from a child: "Is Santa Claus real?"

Many parents want their young children to believe in Santa Claus, but worry about deceiving their kids -- they don't want to lose credibility.

It is possible, however, to have the best of both worlds -- to perpetuate a harmless myth while still maintaining trust -- even in a sophisticated world where 3-year-olds wear designer jeans and 5-year-olds enroll in fast-track, Princeton-prep kindergartens.

It helps if Mom and Dad have some understanding and perspective on the Santa Claus Dilemma.

The first serious study of children's beliefs about Santa was conducted by psychologist Frances E. Duncombe in 1896. She surveyed 1,500 children, aged 7 to 13, in Lincoln, Neb., to determine perceptions of Santa Claus, age of discovering the "truth," how the truth was learned, and whether the subjects thought other children should be taught to believe in Santa Claus.

In 1977, three researchers returned to Lincoln to update this study by asking virtually the same questions of 884 elementary and junior high students. The results, published in Psychology Today (1979), may help today's parents reach their own Santa Solution:

* Super Hero. In the 1896 study, 90 percent of the children saw Santa as a super hero. They were wowed by his ability to slide down chimneys and fly through the sky with his famous reindeer. But modern kids were not so impressed. Only 39 percent viewed Santa Claus as a super hero. Why? Today, he has some tough competition. How do you top He-Man and Wonder Woman? Most kids today consider Santa a nice old man with some semi-impressive powers who hangs out in the toy department of the local shopping mall.

* Age of Discovery. You'd think today's sophisticated kids would figure out the Santa scam much earlier than their 19th-century counterparts. Not so. Duncombe's children learned the truth at an average age of 6.4, while modern children found out the facts at age 7. It's difficult to say why, but remember that children really did grow up sooner in the old days. They had to. Many of them joined the work force after a few perfunctory years of schooling. They were closer to the adult world. They were quicker to accept, if not fully understand, adult perceptions.

* Who Tells. Most children today learn the truth about Santa Claus directly from their parents. The researchers suggest that this probably reflects our present-day preoccupation with being "honest" with our kids. It wasn't always like this. The 1896 study found that most of the subjects learned about Santa from other children -- only 25 percent actually had their bubble burst by Mom and Dad.

* Should the Myth Live? For all their presumptive savoir-faire, today's children believe more strongly (70 percent) than their predecessors (57 percent) that the Santa Claus myth should be perpetuated. They want other kids to experience the happiness that Santa brings -- even if he's only an illusion.

These studies tell us that kids need Santa Claus. In fact, I've found that kids will believe in Santa up to a certain age no matter what their parents tell them. Part of the reason rests in the magical minds of the children themselves. From approximately age 2 to age 7, childrens' cognitive ability is marked by what psychologist Jean Piaget called the preoperational stage, when they do not easily distinguish fantasy from reality. They are not concerned with apparent contradictions. If a child at this developmental stage is told the "truth" about Santa Claus, he may shrug and say something like: "Okay, so he's not real -- but he can fly, right?"

At about age 7, however, youngsters enter Piaget's stage of concrete operations. Now they are capable of knowing and understanding the truth. Of course there's no Santa Claus. How silly. So why do so many 7- and 8-year-olds choose to keep the secret to themselves? It's because they're trapped, for a time, in the no-man's land between fact and fiction, belief and wish. And many kids, while knowing that Santa is a fairy tale, go right on wishing he were real.

Santa Claus, after all, represents a time when things were simpler. Santa knows everything, and children are good in hope that St. Nick will leave lots of presents beneath the tree. Powerful stuff. Hard to give up. Better hedge your bets.

And there's another reason that kids cling to Kris Kringle: They don't want to spoil it for Mom and Dad.

So when a child comes up to you in the next few days and pops the big question, how do you respond?

I suggest that you not be too quick with either the warm reassurances or the cold facts. Instead, let the child show the way. Why is she asking? What does he think?

You may learn something. I did. An 8-year-old looked up at me last Christmas and said: "Doctor, don't be so sad. Santa isn't real -- but he's alive. He's the symbol of giving and sharing.