`EASY' WRITER TRIES SCIENCE FICTION.

After the success of his fifth Easy Rawlins book, ``A Little Yellow Dog,'' you wouldn't think Walter Mosley would consider biting the hand that feeds him.

He's got a popular and critically acclaimed mystery series and counts President Clinton among his fans. His first book, ``Devil in a Blue Dress,'' was made into a well-received movie starring Denzel Washington as Rawlins, a man who coolly navigates the sweltering, casually racist streets of 1950s Los Angeles.

So keep it up, right? Take the ``Easy'' way out. But instead, he's turning to ... science fiction?

Mosley has decided it's time to stretch.

``With science fiction, it's hard to deal with nonreality and have it reflect a powerful emotion, especially without sounding ridiculous,'' said Mosley. ``I know there will be resistance. People are reticent to accept something new from anyone.''

Mosley, a 44-year-old New Yorker, has long stood out in the mystery world. For starters, his hero is black in an extremely white genre. He doesn't rely on serial killers or twisting, turning plots. He created a memorable character in Easy, and he let him do the talking.

To Mosley, stepping away from mysteries is just one more way to measure himself as a writer.

``I think I'm becoming a better writer,'' he says, a cautious tone in his voice. ``I challenge myself as much as I can in each book. Each one poses its own problems.'' For instance? ``Well, in `A Little Yellow Dog,' two of the major characters are dead before the story even starts. And I had to do character development for a dog. If I had known how hard that was going to be, I might not have tried it.

``When you're writing a mystery, plot is every third line. Three lines shouldn't go by and you're not advancing the plot. Sometimes it's subtle, but if you don't do it you have to have a reason why. You're laboring over the plot for the whole book. In a piece of general fiction, you can go much deeper.''

This isn't the first time Mosley has strayed from the genre. Before ``Yellow Dog'' came ``R.L.'s Dream,'' the haunting story of Soupspoon Wise, an old Delta blues man obsessed by memories of the legendary Robert Johnson. It's now out in paperback, and Mosley says readers are paying more attention to it. ``You have to give the world a chance to shift gears about you,'' he reasons.

Mosley himself is shifting them like a race car driver. In addition to sci-fi, he's giving screenplays a crack, writing for HBO. A new book of fiction, ``Always Outnumbered, Always Outgunned: The Socrates Fortlow Stories,'' is coming from W.W. Norton. His previously unpublished first novel, ``Gone Fishin,' '' is being published by Black Classic Press.

Mosley, who says Norton was supportive of the decision, chose the independent black publisher to make a point.

``It's important for black writers to support their literary world,'' he explains. ``It's important to prove that one of these publishers could publish this book.'' Publishers Weekly reported he even waived an advance to make the deal happen.

``Gone Fishin' '' is the story of Easy and his violent, profane pal Mouse coming of age in 1930s Texas. It's not a mystery, but it reads like a prequel to the series. For now, it will have to do for fans of Easy.

Why do readers love Easy? He's no clone of the tough-guy-outside, sensitive-guy-inside detective character. He's complex, caring, but selfish. He knows his way around the seamy side streets, but he takes care of his friends and family.

Of course, Mosley has heard all sorts of theories.

``I was talking to a woman the other night who said Easy is very sexy,'' he said. ``She was very clear to say he wasn't sexual, but sexy. He did all the right things, basically, that a black woman would look for in a black man. And it's not just black women; all kinds of people like him for all kinds of reasons.''

Mouse's appeal may be simpler to understand, even though he's just as likely to shoot you as not. Where Easy is introspective, wanting to make it in the respectable world, Mouse is dangerous - even to Easy, whom he wants to protect. And he's popular, Mosley thinks, because we all want a friend like that.

``Everybody living in modern society, unless they've gained lots of power, feels hopeless at work, hopeless with the IRS, medical bills ... you feel powerless,'' Mosley said. ``Everybody feels that there's a world much bigger than them that they're afraid to face and stand up to. They realize in order to survive, you have to come to some kind of deal. Mouse doesn't do that.''

And although he's taking a sabbatical, Mosley's not abandoning Easy. ``I'll write about him until he's 70,'' he said.

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Photo: Walter Mosley, creator of the Easy Rawlins series (``Devil in a Blue Dress''), is having his unpublished first novel printed and is branching out into science fiction and screen writing.

The New York Times