JUST AS LONG AS WE'RE TOGETHER By Judy Blume Orchard. 296 pp. $12.95

READERS OF my age -- though probably not Blume's intended audience of grade-schoolers -- will immediately recognize the title, a line from the old popular song Side by Side. Stephanie Hirsch, the young heroine, learns the ditty at summer camp. She particularly likes the part that goes "Through all kinds of weather, what if the sky should fall, just as long as we're together, it just doesn't matter at all." And the song comfortingly continues, "When they've all had their quarrels and parted, we'll be the same as we started." In this deceptively simple, multi-layered story, Blume puts these propositions to the test of experience.

This is, I hasten to admit, my first Blume. I'd long heard, of course, about her alleged penchant for off-color subject matter (of which I found no evidence) and her immense appeal to pre-teen readers (of which I found plenty). What I was not prepared for was her enormous skill as a novelist. While apparently presenting the bright, slangy, surface details of life in an upper-middle class suburban junior high school, she's really plumbing the meaning of honesty, friendship, loyalty, secrecy, individuality, and the painful, puzzling question of what we owe those we love.

We first meet 12-year-old Stephanie in the days just before she enters seventh grade. Her family has just moved to a new, somewhat smaller, house not far from their old house, and her father is away on an extended business trip to the west coast -- thousands of miles from their Connecticut home. To someone with more worldly experience, these would be clear signs that something is up, that life will not be the same again. Other things are changing for Stephanie too. As her mother says, she's now "into hunks" in an innocent sort of way; she keeps a poster of the young Richard Gere right over her bed, and daydreams that he is her future boyfriend, but she calls him Benjamin Moore, after the paint used in her new room.

The move to her new neighborhood of Palfrey's Pond brings Steph closer to her lifelong best friend, the earnest, sensitive, studious Rachel Robinson. It also introduces her to a new classmate just arrived from Los Angeles, the savvy, breezy, resourceful Alison Monceau, a Vietnamese orphan adopted as an infant in Paris by a well-known American actress and her French first husband. Alison's family, now including her mother's second husband and a warm, funny step-grandmother, has come east to work on a TV series. So adept is Alison at friendship that the longstanding Rachel-Stephanie twosome quickly becomes an equally harmonious threesome. Even if you can't have two "best" friends, Alison points out, you can still have two "close" friends.

At first it seems that nothing much is going to happen. School starts. The girls speculate about a handsome ninth-grader on their school bus and about when their periods will come. But then, at Thanksgiving, Stephanie's life starts to unravel. Her father comes east for the holiday, but doesn't come home; his stay in California was no mere business trip, but the initial stage of a trial separation. In the first of a series of damaging secrets that destroy Stephanie's peace of mind, her parents neglect to tell the children outright about their problems and plans. To the anguish caused by the split itself, this adds the anguish of betrayal; her parents' inadvertent duplicity wounds Stephanie deeply. The wound festers during a disastrous Christmas visit to Los Angeles, where Steph and her brother encounter their father's rather obtuse new girlfriend.

BUT STEPHANIE, huddled in around the hurt, fails to confide her troubles to her own friends. This leads to a sharp, painful rift with Rachel, who had kept a small but consequential secret of her own. As the months pass and her gloom deepens, Stephanie weighs the various claims that she makes on others and that others make on her. By surrounding her with many different ways of being together -- intact families, broken families, adoptive families, old friendships, new friendships, puppy love, a first friendship with a boy -- Blume astutely leads Stephanie through the maze of her own feelings to a kind of resolution.

In the end, as spring (and her period) come on, Stephanie is reconciled with her parents and with Rachel. (She also realizes she must don her "bee-sting necklace" containing allergy medicine that can save her life if she's stung; clearly her future will bring other problems her way, and she will learn to live with them, too.) And she sees that the song lyrics are at least partially true, but not in the simple way she had originally imagined. The relationships that matter can survive even if "the sky should fall," but the people won't necessarily emerge "the same as we started." The important thing, Blume seems to say, is working at staying together even as things change.

Beryl Lieff Benderly is the author of the newly published "The Myth of Two Minds: What Gender Means and Doesn't Mean."