THINGS INVISIBLE TO SEE by Nancy Willard (Knopf: $14.95; 236 pp.)

In the interest of letting their readers know what to expect of the books they buy, publishers might consider branching out from blurbs and flap summaries. For example, they could print on the jacket the names of any animals to be encountered.

There is a cat in Nancy Willard’s romantic fantasy, and it is called Cinnamon Monkeyshines. That tells you something. If the name strikes you as warm and inveigling, “Things Invisible to See” is likely to inveigle you. If not, possibly not.

My own feeling about animals is that generally they would be better off with numbers. I realize that puts me at a captious extreme from the Cinnamon Monkeyshines camp. Perhaps the fair thing is to stand a little apart from judgment and take a presentational approach, the kind sometimes used with the newborn: “My, that is a baby.”

My, this is a romantic fantasy.

It begins with God playing baseball with a pickup bunch of archangels. Every time God pitches, some change takes place in the destinies of the amiable folks in Ann Arbor, Mich., around whom this pastoral-magical Popsicle is confected.

The hero is Ben Harkissian, whose mother works in a dry-cleaning shop. Ben is the good brother; his twin, Willie, is the bad brother. At conception, we are told, they argued about the qualities each would have. Willie chose brains, and Ben was left with charm and good looks. Ben emerges dreamy, kind, a terrific southpaw pitcher and a trifle fey (when he fixes toilets, they sing “The Star-Spangled Banner” and when he uses a vacuum cleaner, it picks up nothing but gold). Willie is a miser, a schemer, a crook and finally, a Cain to Ben’s Abel.

One night, in the park, Ben hits a stray ball which beans Clare Bishop, leaving her paralyzed from the waist down. Enter the Ancestress, a part-time guardian angel who ferries Clare’s spirit around so that it can opportunely inhabit assorted animals and inanimate objects, and do good.

Ben and Clare have a gentle love affair. Ben goes to war and is marooned on a raft in the Pacific. He wagers his life with a personage called Mr. Death upon the results of a three-inning ballgame to be played between his friends on the one hand and the ghosts of such as Lou Gehrig and Christy Mathewson on the other. After various twists and turns, the young men find themselves unable to play--they being in the hospital as a result of a murderous attempt by Willie--and their female relatives stand in for them. The pitcher is Clare, who has recovered her legs. They win, and goodness and happiness prevail over Mr. Death, Willie and other assorted graspers.

Willard has written poems, short stories and a number of children’s books. “Things Invisible” is told something like a children’s book for grown-ups. The characters devise into quite marvelous and quite awful. The whimsies are cut to large and extra-large sizes.

Some of them are funny and crisp. Two sisters are so close and prickly that one of them can smell the scorch of the other’s ironing when they are talking by phone. They share responsibility for an amiable old father and an impossible old mother, swapping them regularly and keeping track of mother days and father days in an account book. When Ben’s first girlfriend, who is rich and pushy, takes him to lunch at an expensive restaurant, he says that everything looks good, and she proceeds to order literally everything and expects him to eat it.

On the other hand, the magic interventions are put to a lot of work to advance such a sweet and small plot. Willard’s supernatural is as cozy as a long Sunday afternoon with the heat turned up. There is some highly adorned language. Willard uses such phrases as “God, who watches and winds the footage of humanity. . . .”

She is an exuberant and fanciful writer, but she over-arranges her tale. If “Things Invisible to See” were a refrigerator, it would be ornamented with kittens and quotations from William Blake.