Seven-year-old Rudolph Hines is a child of few words. Ask him if he likes being pen pal with the president of the United States and the bashful second grader says simply "yes."

But put him in front of a blank computer screen and Rudolph can suddenly think of all sorts of things to say. He writes to President Reagan at least once a month about everything from his painting hobby to how he did on his latest report card.

Rudolph is one of a number of youngsters at Martin Luther King Jr. Elementary School in Anacostia (formerly Congress Heights Elementary School) who have pen pals at the White House, which "adopted" the school in 1983.

Unlike many children who find writing a dreaded chore, Rudolph and his classmates think it's fun, their teachers say. Many of the children have been writing one thing or another since they were in kindergarten and became involved in an experimental software program called "Writing to Read."

The program, marketed by IBM and given high marks by the Educational Testing Service, the Princeton, N.J., firm which administers standardized tests to American students, is one of a growing number of educational programs and software that use the computer to teach youngsters a fundamental skill: how to write.

Learning to write is crucial, educators say, because good writers inevitably are also good readers.

The programs, which include an electronic news service run by elementary school students, are creating excitement among educators concerned about the growing illiteracy rate in this country.

That illiteracy, they say, has been caused in large part by the pervasiveness of such technological wonders as the television, telephone and video games.

"Since the age of technology, writing has decreased in our society. We tend to pick up the phone rather than write a letter," says Linda Leonard Lamme, a professor of education at the University of Florida and author of Growing Up Writing (Acropolis, $8.95), a parents' guide to literacy skills.

"But the computer," says Lamme, "with its word-processing capability, has encouraged a lot of children to really become avid writers, to go back and write longer stories, to stick with a story.

"They take more risks when they write because they can change it; they can revise it. They do a better job of writing."

Lamme is concerned, however, that many parents with home computers are not encouraging their children to use them as a writing tool. She points to a recent survey of 1,000 parents around the country whose children subscribe to Highlights for Children, an educational magazine. A whopping 67 percent of the parents with a home computer said they thought it has had no effect on their child's writing ability.

"This means that the children at home are doing other things with their computers," says Lamme. "Parents need education on the thoughtful uses of computers."

Says Bernice Cullinan, president of the International Reading Association: "I don't think parents have thought much about the computer as a tool for writing yet. They are using the prepackaged programs, but I don't think they're encouraging the use of word processing.

"The evidence we have now is that the computer is going to help kids write more. Once they are old enough to master the keyboard, it really frees them up. It's like gangbusters when they hit that stage where they can compose on the computer. It increases their writing tremendously."

Simply sitting children down at a blank computer screen and telling them to write, however, may be just as threatening and nonproductive as handing them a blank piece of paper, cautions University of California (San Diego) research psychologist Margaret Riel.

"Kids aren't ready for that much power," she says. "They need more direction."

Riel prefers more "interactive" programs like electronic story makers, which allow novice writers to choose from a list of preprogrammed options as they weave their tales. She and her colleagues have produced a number of such writing aides through InterLearn, an independent software company they formed in 1983.

One program, The Poetry Prompter (InterLearn, $39.95) includes examples and descriptions of different forms of poetry to help kids get started. It also allows young poets to write their own versions of the children's classic "A Visit From St. Nicholas" by substituting key words and phrases based on other special occasions such as Halloween or summer camp.

A pilot group of San Diego-area fourth graders spent a school year working with the interactive writing programs and the Computer Chronicles Newswire (InterLearn, $69.95), a computer program that teaches kids how to write newspaper articles, which are distributed electronically to participating school newspapers.

The experimental group started out below the California norm in reading and language skills. By the end of the year, according to Riel, their language scores on the California Test of Basic Skills had jumped two to three grade levels. She believes one of the key factors in the program's success was the children's experience of producing news stories they knew other people would read.

"Once they were able to look at their stories from the point of view of an audience," says Riel, "they were more conscientious about the kind of details they included." The children took great pains to rewrite their own and one another's material, she says, to make sure it was clear and well-written.

The IBM Writing to Read program, tested in 15 D.C. schools and 210 other schools around the country before going on the market last summer, also significantly improved kindergartner's and first graders' scores in both writing and reading tests, according to the Educational Testing Service's evaluation.

Children in that program (which costs more than $15,000 per classroom) don't actually write on the computer; it is used, along with a voice component, to teach youngsters phonetic spellings of a number of words.

It's easier for 5- and 6-year-olds to spell a word the way it sounds than to master the quirky, exception-laden spellings of the English language, explains Thelma Michael, coordinator of the D.C. school system's Writing to Read program. If they don't have to worry about correct spelling, she says, youngsters can draw on their large speaking vocabularies instead of being limited to only those simple words they already know how to write.

The result is "amazing," says Michael. "Traditionally, we have not even thought of having 5-year-olds express themselves through stories. The kind of writing you'll see these children doing would not have come before the latter part of first- or second grade."

Writing-to-Read students actually write their stories longhand, then revise them and type final drafts on an electric typewriter.

That return to more traditional writing tools has baffled some education experts like Kenneth Komoski, executive director of the Educational Products Information Exchange (EPIE), a nonprofit agency that evaluates educational software.

Says Komoski, "I'm not putting down the program. It's a very valid, very effective way to teach Americans to read. But the idea of turning to the typewriter for writing is ludicrous. There is no question that word processing is a wonderful way of improving one's writing."

But until the number of computers in American schools is increased greatly, children must get most of their writing practice at home, he says, on their own word processors. (Despite a 100 percent growth in the number of computers in schools last year, there is still only about one computer for every 60 students, according to Komoski.)

"Can you imagine running an office," he asks, "where everyone is supposed to be writing with one computer for 60 people?"

In Alexandria, public elementary schools have used the Bank Street Writer (Scholastic, $95) -- word-processing software designed specificially for children -- for more than a year and are in the process of acquiring two other electronic writing tools. One will teach students to organize and write business letters and reports, and another will assist them in keeping personal journals.

Although James Akin, director of Alexandria's elementary education, concedes the school system's computers are used infrequently to help kids learn to write because many teachers have not yet been trained, he plans to beef up that training this year.

"When computer literacy first started," says Akin, "it grew out of the math departments, which taught programming with mathematics applications. But with the development of the Bank Street Writer, educators are seeing that one reason kids have difficulty learning to write is that it is so laborious.

"They lack the fine motor skills necessary to write longhand . It has restrained their writing. Then the red marks of teachers and the need to copy over defeats them."

The computer, he says, makes rewriting a snap. "The key to good writing is editing."

But won't all this electronic writing make good penmanship a lost art?

"What do you need good penmanship for?" asks New York educator Gwen Solomon, author of a forthcoming book, Teaching Writing with Computers: The Power Process (Prentice-Hall).

"Generally, you can read your own handwriting. What you're going to show people will usually be typed."