With a determined gleam in her eye and an intense smile on her lips, the handsomely dressed woman looks like the star performer in a "bowling-is-fun" commercial.

Left arm extended full length for balance, the woman sweeps her right hand smoothly back and hurls the orange ball straight and true down the lane. When it strikes the target at the far end a few seconds later, the soft thud of contact is drowned out by a resounding cheer from the spectators.

A familiar scene in many ways, but the setting here is not your local bowling alley, and the woman makes no claim to skill at tenpins. The "bowler" in question is Nancy Reagan, and the "strikes" she rolls with a fresh orange each time her husband's campaign plane takes off have become an unfailing ritual of the Reagan-for-President campaign.

Every presidential campaign -- or at least every one that can afford to charter its own airplane -- turns into a world of its own in which the candidate, the staff, security agents and the press are joined by proximity and shared experience into a family, of sorts, with a lore and language all its own. And every campaign seems to develop a cherished treasury of in jokes, nicknames and rites that have no meaning except to the participants.

Even within this rich tradition, however, Nancy Reagan's contribution to American campaign ritual seems unique.

She has accompanied Reagan on most of his campaign trips this fall on his chartered jet, a stretched-fuselage Boeing 727 that is officially named "Leadership 80," but is known to the traveling press corps as the "Ponce de Leon" (and some other names not fit to print).

Each time the campaign plane roars upward from a runway, Mrs. Reagan assumes a position in the center aisle at the head of the plane. Looking as competitive as a professional athlete who has thousands of dollars riding on the next shot, the 57-year-old former actress carefully bowls an orange down the steeply banked aisle and watches intently to see if the missile can travel all the way to the plane's rear door without running astray amid the seats and bulkheads.

If she succeeds, Mrs. Reagan smiles broadly and graciously accepts the laughs, whistles and shouts of approval from her fellow travelers. But if the orange smashes midway into a foot or briefcase or seat, she calls for another and tries again -- sometimes half a dozen times -- until she hits the mark.

Immediately after she rolls her strike, Mrs. Reagan begins the second half of her take-off routine. She strolls down the aisle, balancing with practiced ease as the plane lurches upward to its cruising altitude, offering chocolates to every one on the plane.

There are no exceptions to this litany. If Reagan's plane takes off four times on a given day, his wife will roll oranges four times that day. And the campaign staff will lay in four boxes of chocolates for her to pass around.

Mrs. Reagan has a simple explanation for her pastime. "Well, it's fun," she says, and in the exhausting whirlwind of coast-to-coast campaigning that has been a way of life for Reagan and his entourage all year, everyone on the plane agrees that this rationale is quite enough.

"We're at 200,000 air miles and counting," says a cameraman from one of the television networks."You've got to find something to make it fun, or you'll go bananas."

The cameraman's "something" consists of an imposing collection of noisemakers he carries in his pockets, on his electronic gear and attached to a chair around his neck.

"Let's see," he said during an impromptu inventory last week. 'I've got my frog chirper, my cab whistle, my [London] bobby's whistle, my Acme screamer, and my L.L. Bean duck call. And then of course I've got this bicycle bell on my camera, and. . . ."