ON THE EIGHTH anniversary of the first moon landing, former astronaut Edwin E. (Buzz) Aldrin is busy trying to launch some science fiction.

The second person to step onto the moon while the world watched from below. Aldrin suffered severely from the anticlimatic aftermath. In some versions his discontent started with the fact of being second, rather than first. He than became alcoholic and depressed, from disorientation and purposelessness. In the last year, however, he has overcome these problems, gone into several business ventures and started to writes stories about people engaged in space travel from the direction opposite the one he took - coming from outer space to populate the earth.

The stories are being written with Roland Barber, a magazine and television writer, and Aldrin has been in New York this week, taking them to publishers. Aldrin was not a science fiction fan before becoming an astronaut. He remembers doing an eighth grade paper on science fiction and being told by a teacher that it was not literature. But now that he wants to write, he selected the genre as allowing him "to build on the foundation of what knowledge I've accumulated."

Science fiction, he believes, should be "a technological projection of what we know. Flash Gordon and Buck Rogers were good, because they somehow represented the best imaginative thinking, the best educated guesses." But the popular film "Star Wars," in his opinion, "may well kill it all off. That's nothing but World War II fighter stuff, or gangbusters. I'd hate to think that represented our best guess about the future."

The first Aldrin-Barber story, "Centauri Descent," is about four "elders" and four apprentices from the star closest to our sun, who make a 40-year trip to earth, "a long, long time ago." The plan is to have the younger members of the crew raise children to make the return trip, but they stay; they turn out to be our ancestors. In the second story, which takes place 150 years later, commuting time is reduced to 10 years, and a later generation comes from Centauri to see whatever happened to the earlier crew.

So how come it has taken us so long to develop technology that is not as good as our ancestors'? "People like to envision uniform progression, but it doesn't necessarily happen that way," said Aldrin.

Aldrin's personal progression was chronicled, up to 1972, in a television film called "Return to Earth." It explained his post-flight breakdown, and ended with him walking along the beach with his estranged wife, while a tape of Apollo II was played in the background.

Subsequently, Aldrin and his wife were divorced; he married again, on New Year's Eve, 1975, and he and his second wife are now separated. He had not been "all that well" when they married, he said - it was only a year ago, in May, 1976, that he acknowledged his alcoholism, from which he is now "recovering." "You're never cured. I don't drink now."

Earlier this month, he became director of sales and development for the Hillcrest Motor Co., a Beverly Hills, Calif., Cadillac dealership. He is a consultant to two electronics firms and to a solar energy company. He is also active in the National Association for Mental Health.

And the only space dreams he has are about getting his stories made into a movie or television series.