Alan John Hu won the top scholarship of $12,000 last night at the 44th annual Westinghouse Science Talent Search in a ceremony at the Mayflower Hotel. Hu, 17, a senior at La Jolla High School in California, plans to study mathematics and computer science at Stanford University. His contest entry was a system to reduce the time spent finding records on computer files. He also won first place at last year's International Science and Engineering Fair.

Hu was first of 40 winners from 13 states and Puerto Rico who competed for $89,500 in scholarships and awards. The immediate runners-up in the competition were (in descending order):

* Anna Asher Penn, 17, of Chicago, for analyses of certain viruses using DNA clones of a bacterial virus. She won $10,000.

* Michael Friedman, 17, of Brooklyn, N.Y., for a number theory research project. He also won $10,000.

* Michael Steven Graziano, 17, of Buffalo, N.Y., for an analysis of current theories involving the relationship of the left and right sides of the brain to human motor tasks.

* John Shu-Shin Kuo, 17, of New York, for a study of microbial genetics.

* Anthony Mario Ciabarra, 17, of Wyncote, Pa., for a study of an unusual DNA repair mutation. Graziano, Kuo and Ciabarra each won $7,500.

The $5,000 winners were Mark Kantrowitz, 17, of Brookline, Mass.; Michael William Gesner, 17, of Avon, Mass.; Audrey Zelicof, 16, of New York; and Allan Moises Goldstein, 17, of Wyncote, Pa.0500000126:

Parents don't have to wait until their children are old enough to master the computer keyboard to encourage them to write, according to educator Linda Leonard Lamme, author of Growing Up Writing (Acropolis, $8.95).

"Give the children a marker at the age of one year," she advises. "They'll love it. It's absolutely amazing what you'll see. They'll start scribbling and very quickly will start differentiating in their scribbles between writing and drawing.

"After tons and tons of scribbling experiences, they will start making letter forms. We call them mock letters."

But there is no need to encourage very young children to learn to write the alphabet, says the University of Florida education professor. "The alphabet is fairly meaningless to them. What parents can do is to write notes for their children and take dictation. The alphabet will come because the alphabet is in all the writing they see.

"We encourage kids to play with oral language. We let children say 'ninny' and 'nanny'. Well, children love to play with print. They'll color in your letters; they'll trace around them; they'll underline. And they'll learn what letters are like, what words are."

The most important thing, says Lamme, is to praise those early attempts at writing. "There have been several studies showing that when children draw, parents say 'Oh good, isn't that a nice picture.' When children read, they are usually supportive. But when children write, all they do is criticize. 'Gee, you haven't crossed your T. You haven't spelled it right.' They don't look at what the child is trying to communicate."

Parents should focus on what children are trying to say, says Lamme, and encourage a love of writing instead of worrying about grammar or spelling. "There's time when they get older to edit, to revise. When they're little, let them have a good time. Be supportive."

That way, she claims, children will grow up "hooked on writing."