Laughter stands alone, but a cry needs a why; Victory Over Japan, by Ellen Gilchrist. Boston: Little, Brown & Co. 277 pp. $15. 95.

Why, I began to wonder, near the end of Ellen Gilchrist's new collection of stories - why are some of these stories such a pleasure, and others so unsatisfying? Then I struck this passage:

''Sometimes I start telling a story that's sad and the first thing anybody says is how come? How come they went and did that way? Nobody says how come when you tell a funny story. They're too busy laughing.''

That explained it. Sad stories, when they're well told, at least hint at a rationale, a meaning to the pain. Otherwise they're just journalism. And that's what Gilchrist's sad stories seem like - well-written journalism. Her comedy is more artful.

Her style has a lot to do with it. Her sentences are utterly unadorned, and would seem banal, were they not joined together in lively, expertly modulated rhythms. It's a style well-suited to wit and surprise but ill-equipped for expansion and reflection, the ''how come?'' that sad stories require.

It isn't surprising that Gilchrist's most successful character is a child, Rhoda, the precocious heroine of the first two stories. Rhoda doesn't stop to reflect on her misfortunes - a bullying father, a bedridden boyfriend. Her heart stays light. Anything can happen to a 14-year-old. But what's caprice in a child often seems like shallowness in Gilchrist's adults. If anything can happen, then nothing makes a difference.

So it's hard to care about Nora Jane, who's pregnant, unwed, and unsure of the father; or about Miss Crystal, who's an alcoholic and a marriage wrecker. Their mistakes have no consequences and therefore seem trivial.

If fancy alone made fiction good, then Gilchrist would be a master. Her stories are full of hilarious antics. But we want to know more than what happened. We want her to suggest why.

We want to hear, did we miss an angle we should have covered? Should we come back to this topic? Or just give us a rating for this story. We want to hear from you.