BOSTON -- I have a young friend who will tell you, if you ask, that she grew up in an ''intact single-parent family.'' It is a phrase she invented some years ago when she got tired of hearing her family described in pathological terms.

She and her mother were not broken. Her home did not operate on crutches. She was not ''a child of divorce,'' but a child of two parents who no longer lived together.

My young friend was making a point. All single-parent families do not come in one flavor: weak. There are as many varieties as among two-parent families. Hers tasted strong. I thought of her last week when the Census Bureau released its figures. Nearly a quarter of all American children now live with one parent. More than half will spend some time in a single-parent household before they are 18.

Two-thirds of these households are created by divorce or separation. Most of them, 89 percent, consist of a mother and children. What was once a deviant pattern has become ordinary.

In deference to my friend, we might subdivide this category into its meaningful parts. After all, the real-life experience of a child of shared custody is different from the experience of a child with a parent who disappeared. The life experience of a child who slides down the economic chute is different from that of one who remains financially secure.

A toddler's experience with divorce is, in turn, different from that of a teen-ager. A child whose parents remain bitter has a different life from the life of children whose parents are personally happy and civil to each other.

You cannot walk the city streets and pick out the telltale signs of someone who grew up with one parent. There is no pathology of single-parentness. Yet I know there is something shared by the children counted by the Census Bureau. An experience of loss. A feeling of impermanence. An altered sense of security. And maybe even the hope that it won't happen to their own.

Offspring of the strongest single-parent households, those kids who made it, those who can explain by 14 or 15 precisely why their parents couldn't live together, who can negotiate their way between two households, perhaps even two new families, share these feelings. Push a bit into their cool surface and you can touch a warm spot of sadness.

The word ''family,'' narrowed down to its nucleus, evokes primal feelings. The college-age students who watch afternoon reruns of ''Ozzie and Harriet'' don't just tune in for its camp humor. There is also a hunger for entry into those dated vignettes. To be mom and dad and us kids for a half-hour.

Even the competent, independent teen-agers who become partners and confidants to their divorced parents carry with them another model of the perfect family. What family would they like to live in if they couldn't live in their own? I expect they share the majority's choice: ''Family Ties.'' Do they want Michael Fox as a brother? The other fantasy -- two parents clearly in love, two parents they can talk to -- is more compelling.

Once a single parent myself, I often wonder how the 50 percent of children who spend time in one-parent families will fashion their own. One childhood experience sends different internal memos to the future.

Some may shy from marriage. Others may leap needfully, prematurely, into the business of creating a family. Some may take themselves as proof that children survive divorce. Others may find the opposite evidence.

Probably the children of single-parent families will try to correct their elders' mistakes. We all do that. One generation vows they won't do what their parents did: stay locked together in a dead marriage. The next generation vows they won't do what their parents did: split.

But what comes through all the change, all the statistics, what remains as clear as the grain of the wood under a dozen coatings of stain, is a constant ideal of mom and dad and us kids. It may be as elusive as the images on a television screen, but it's just as powerful.

Life in the Census Bureau's single-parent households is indeed as diverse as life in two-parent households. But today 50 percent of our children, even those in an ''intact single family,'' will grow up knowing what it's like to feel that something -- someone -- is missing.