Time Inc. announced yesterday that it has purchased Science 86 magazine from the American Association for the Advancement of Science for approximately $7 million.

The sale, which had been expected for weeks, spells the end of the award-winning, but money-losing, Washington publication. Time plans to fold Science 86 into its own award-winning Discover science magazine, effectively eliminating its strongest rival in the troubled science magazine category.

"It's a terrific magazine, and it's a shame," said Gilbert Rogin, managing editor of Discover magazine, "but it's not even clear that one magazine can survive in this field."

"Deciding to cease publication of Science 86 was an extremely painful decision for the AAAS board to make," said President Lawrence Bogorad in a statement. "It was necessitated by the severe two-year decline in advertising revenues, which has put a tremendous strain on the budget of our nonprofit organization."

According to Publisher William Carey, advertising had fallen by half over the last two years.

The Science 86 sale highlights the troubles and uncertainties that have plagued the science magazine category. Time's own Discover has lost millions of dollars and gone through an editorial shake-up since its 1980 founding.

Similarly, Hearst Corp.'s Science Digest is a money-loser, and the once-robust Scientific American is up for sale.

While profitable in its early years, the 7-year-old Science 86 (which changes the number in its name each year) was unable to overcome its slump in advertising sales and, like the other science magazines, fell victim to a crowded category.

"I think it's a tragedy and I'm very sorry," said Science 86 editor Allen Hammond, who said that attempts to find an 11th-hour publishing savior for the magazine failed.

"This really gets us on the road," said Discover Publisher James B. Hayes. "This gives us the opportunity to become profitable; it gives us a juicy advertising sales opportunity" because Discover does not plan to raise its advertising rates, even with the addition of the Science 86 subscribers.

Discover has an advertising rate base of 850,000 readers, while Science 86 had 700,000. According to Hayes, Time "anticipates some 35 percent of Science 86 subscribers converting to Discover" -- which would give the magazine substantially more than 1 million readers.

Hayes said Time is discussing options for making good on subscriptions that are not converted to Discover. He said the company may offer cash refunds or subscriptions to other Time publications.

"Most of our fears as to future profitability have been arrested with this," said Hayes.

He also confirmed that Time was interested in acquiring certain assets of Scientific American -- notably its W. H. Freeman book division.

Folding Science 86 is a particularly bitter pill for the AAAS because, as a nonprofit institution, it has a charter to promote public understanding of science. However, the association's board apparently felt that it could not afford to subsidize the magazine's losses, which have approached $1 million a year, according to AAAS's Carey.

More than 60 employes in Washington and New York are affected; severance terms have yet to be revealed.

There were no other "conclusive" bidders, said the AAAS.