A renowned science fiction writer shot and killed her ailing husband and then herself in the couple's McLean house early yesterday, apparently carrying out a pact to die if living became too difficult, Fairfax County law enforcement officials said.

The bodies of Alice Sheldon, who wrote under the pseudonym James Tiptree Jr., and her husband Huntington Sheldon, a former CIA analyst, were discovered in their bedroom with bullet wounds in their heads after police received a call from the couple's attorney at 3:34 a.m., police said. Alice Sheldon was 71 years old; her husband was 84.

"She left notes indicating she was going to do it," said Commonwealth's Attorney Robert F. Horan Jr. "Evidently there was some sort of pact between them . . . . It appears that her husband's health was increasingly becoming more difficult for him."

Friends of Alice Sheldon, whose popular works include "The Women Men Don't See," "The Screwfly Solution" and "Love Is the Plan, the Plan is Death," described a devoted couple with a number of medical problems and a husband who was bedridden and blind.

In a Dec. 28, 1976, letter to writer and friend Robert Silverberg, Alice Sheldon talked about killing herself: "I had always meant to take myself off the scene gracefully about now while I am still me. And now I find I can't, because to do it would mean leaving him alone, and I can't bring myself to put a bullet through that sleeping head -- to take him too, when he doesn't want to go . . . . "

Huntington Sheldon retired from the Central Intelligence Agency in the late 1960s, where he was an intelligence analyst and "a distinguished agency employe," said spokeswoman Kathy Pherson. The Sheldons lived not far from the agency, at 6037 Ramshorn Place, on several wooded acres, where friends and neighbors said they cherished their privacy.

Friends said Alice Sheldon, who has written several dozen science fiction works, used a pen name in part as a way to keep her private life separate from her publishing world.

In a review in The Washington Post last year, Sheldon was described as one of "the finest writers of short fiction to emerge in the '70s" and as someone who "stunned the community when it was revealed that he was a she, Dr. Alice Sheldon of McLean, Virginia."

"There was real shock in the field when it was revealed just who James Tiptree Jr. was," said Beth Meacham, editor of Tor Books, publisher of Sheldon's latest novel, "Brightness Falls From the Air."

Silverberg, who described Sheldon as "brilliant," "powerful" and "unique," said he, too, had been convinced that Tiptree's books could have been written only by a man because of the writing style and experiences, including expertise on guns.

He said that he wrote an introduction to one of her books stating as much and that Sheldon later wrote him a letter, apologizing profusely for misleading him.

Sheldon's identity was revealed after the death of her mother, Mary Hastings Bradley, a well-known geographer and travel author, said literary agent Virginia Kidd.

She said the revelation was crushing for Sheldon, who for more than 10 years had assumed the pseudonym, and it plunged her into a deep depression. Long beset by medical problems, Sheldon had been "threatening to commit suicide for the last 20 years," Kidd said.

In what they called a murder-suicide, Fairfax police found her husband shot twice in the head and Sheldon shot once, Horan said. Alice Sheldon had called the couple's lawyer, who called police, police said. The prosecutor said Sheldon was "incredibly organized" and left behind detailed instructions about the couple's affairs.

Born in Chicago, Sheldon spent much of her childhood in Africa and India and was employed by the U.S. government for many years, including work for the CIA. Sheldon acquired a PhD in experimental psychology and conducted research for many years before she retired.

By most standards, she began writing late in life, and most of her award-winning work was written in short forms and with astonishing speed, beginning with "Birth of a Salesman" in 1968. Other works include "Warm Worlds and Otherwise," "How to Have an Absolutely Hilarious Heart Attack" and "Tales of the Quintana Roo."

In her story "The Women Men Don't See," a pair of American women, vacationing in the Yucatan, encounter stranded humanoid aliens, establish contact and eventually blast off with them, deciding that life among aliens has to be an improvement over that with men on earth.

One reviewer described "Tales of the Quintana Roo" as having "all the flavor of Tiptree but little of the meat, little of the tightrope-walking complexity of her more extended work, where one plot is never enough, nor one climax, nor one neat message . . . . " The reviewer went on to describe her as a writer of "fiery acumen, psychologically acute, sharply compassionate."

It was those qualities that two close friends, standing outside the Sheldons' house, recalled most vividly yesterday.

"They lived a beautiful life, very loving," said one friend. Crying, the other added: "They were very vital, intelligent people. They were finding life very fragile right now."