Boston — As Ben Bova settles back into a sofa in the lobby of a posh Boston hotel, his wife, Barbara, warns him he is about to spill his cup of coffee on his lap. ''That wouldn't happen in zero gravity,'' he quips, righting the cup just in time. Clearly, Mr. Bova, vice-president of the National Space Institute and the author of more than 55 science fiction and science-related books, thinks in cosmic terms. Whether the subject was Skylab, sundaes, or the future impact of space technology, his frame of reference was worlds apart from the hotel's Victorian milieu.
''The really fascinating thing about science fiction is, as an artist, it gives you an enormous canvas,'' says Mr. Bova, whose books appeal to both teen-age and adult audiences. ''In science fiction you are free to invent anything as long as no one can prove you wrong.''
At the same time, Mr. Bova is not a fantasy writer. Although his books are not confined to the immediate stage of the space industry, they are based on scientific facts as far as they are known.
Science fiction fans applaud the credibility of his scenarios. But it is a sense of humanism that carries Mr. Bova's work beyond a simple fascination with fancy technology.
In ''Escape,'' a longtime favorite book among high-schoolers, a juvenile offender is put into a futuristic correctional facility run by a computer and, in the process of trying to escape, learns to be a good citizen. Another popular book, ''Test of Fire,'' involves a contest of wills between a boy and his father.
''From its origins, there has been a strong streak of education and moralism in science fiction,'' says Mr. Bova. ''No one really writes about the future - they write about the problems bothering us today.''
Still, his ethical themes are wrapped in enough galactic excitement to encourage even ''reluctant'' teen-age readers to keep turning the pages.
''Science fiction has become a way to get youngsters reading, period. It appeals to kids,'' he says. ''It's a genre of fiction in this country with a sense of adventure and optimism.''
Through his books Mr. Bova also hopes to tantalize young people with the opportunities opening up in the science and space fields. ''You don't have to be an astronaut or a jet jockey to have a job in the space industry,'' he says. ''There are thousands of jobs on the ground.''
Mr. Bova's own fascination with space began as a young boy in South Philadelphia when he visited a nearby planetarium. ''He saw the stars turned on and it turned him on,'' says Mrs. Bova, who believes it's up to parents to spur their children's interest in science and space by taking trips to science museums, planetariums, and the local library.
After working as a reporter for several years after college, Mr. Bova joined Project Vanguard, the first American satellite project, as a technical editor. Later he became manager of marketing for Avco Everett Research Laboratory in Massachusetts, where he worked with scientists developing high-powered lasers and sophisticated electrical power generators. He has also served as editor of Analog and Omni magazines and as a technical adviser for science fiction movies.
Currently Mr. Bova writes from his home in West Hartford, Conn., and is the science and technology commentator for the CBS Morning News.
''The electronics we developed to get to the moon are now coming into our homes as video games and home computers,'' he says. Some people see computers as dehumanizing, but not Mr. Bova. ''The computer screen is a window on the universe. (In the future) you will be able to bring all the education in the world into your own home,'' he says.
In addition to the scientific advances, Mr. Bova is also intrigued by the more aesthetic aspects of life once people start living in space on a long-term basis - already a present reality in the Soviet Salyut 7 space station.
''I've long been interested in how people will dance in zero gravity,'' he muses.
In the meantime, Mr. Bova hopes to be the first in line when NASA allows civilians in space as passengers on space-shuttle missions. ''It could happen sooner than people think,'' he says.