AT THE WHEEL OF HER CHRYSLER CONVERTIBLE, Diana Friel McGowin is speeding along Stale Road 44 from her home in Orlando, talking about preparations she has made for her death. "I have the tapes of the music selections for the funeral, and they'll stand my pastor on his ear—'Moonlight Sonata' by Beethoven and Elvis Presley's 'Forget Me Never,' " she says with a laugh, then gives the accelerator a playful tap.

Two years ago, McGowin, 55, was diagnosed as having early-onset Alzheimer's, a version of the physically and mentally degenerative disease that strikes millions of old people. The main difference, McGowin points out, is that "the elderly diagnosed with Alzheimer's have already Left their careers, already segued out of the mainstream of their family. For us, all that is taken away. It is such a trauma to know that your body is going to outlive your mind." So, while she can, McGowin is fiercely pushing the envelope.

She has devised ways to cope with her memory loss—keeping maps to the grocery store in her pocketbook, taping a daily reminder of the day, month and year on her refrigerator. She has removed all the dish towels from her kitchen because, she says bluntly, "I am a fire hazard." And she has become an advocate: giving speeches for the Alzheimer's Association, launching one of the nation's first support groups for early-onset patients and writing her first book, Living in the Labyrinth, a searingly honest account of her struggles with the disease.

The 130-page book was published last year by San Francisco's Elder Books, a small house that produces materials for Alzheimer's patients. But the themes McGowin touches on—death, disease, loneliness—have resonated widely. The 3,000-copy first printing is nearly exhausted; a second printing is in the works, and Delacorte will publish a hardcover edition this fall. Says Mary Ellen Ort-Marvin, a board member of the Greater Orlando Alzheimer's Association: "Diana is saying, 'Look at me and see yourself. This is the humanity of a deadly disease.' "

McGowin, a legal secretary before illness struck, began keeping a journal at the recommendation of her physician, who suggested that a word processor could function as her memory. A counselor in the doctor's office urged her to continue her writing, with the idea of eventually publishing some of it.

It was slow going: Some days the words would make no sense. But in the end, McGowin's eloquence overcame her disease. A sequel to Living in the Labyrinth is now under way. McGowin will donate part of her royalties to Alzheimer's research. "People say I should be thinking of my own long-term care because my husband and I don't have the kind of money we'll need," she says. "But I felt it was too fatalistic to be salting the money away for that, when I could give it to researchers who might save my ass."

In McGowin's mind, nothing she has done is particularly courageous, though that word is often applied to her. "The Webster's definition of courage is when you deliberately walk into the face of danger," she says. "I did not volunteer for Alzheimer's. I'm the most frightened of them all, and that's why I go around trying to spread the cause. Because when I focus on the positive, it keeps me from becoming overwhelmed by my own terror about my future."

When Diana Friel was growing up in Wilmington, Ohio, her parents, a fireman and a homemaker, suffered for their gifted older child. "My mother would cry after teacher conferences," she recalls. "I realize now the teachers were telling her I should go to college, but my parents knew they'd never have the money."

In fact, Diana didn't get to college until she was in her 30s and supporting a daughter and a son from a failed marriage. Juggling her paralegal courses with work and family proved too much, and she dropped out after two years with a perfect 4.0 average. In 1967, she married John McGowin, a security officer. They had a son, Spencer, now 23, and the family settled into a three-bedroom house in Orlando.

In 1989, Diana began suspecting something was wrong. She couldn't find her way from her desk to the rest room at work. She wasn't able to recognize people she'd known for years. Some days she couldn't find the laundry room at home. She pressed her doctors for a diagnosis, but it wasn't until 1991 that a series of brain scans suggested the worst.

Black days, as she calls them, followed, especially when she decided she had to quit her job. "Deep down, when you first start having this problem, you think you might be losing your mind," says McGowin, who spent days alone in a darkened house. "Then there's the shame."

Her husband exacerbated her insecurities. "John would deliberately lose me in a store, hide somewhere and watch me go through my panic," she says. "He wanted to see if I was still able to figure my way through the situation, but in my reasoning he was putting me through hell. At a time when I was truly at the end of my rope, I would have licked his boots if he could have just given me some moral support."

John admits he didn't react well to her illness. "I didn't want to accept it," he says, "and I did some things I regret." The marriage has survived, McGowin says, because she values its "comfortable familiarity" and John has gradually grown more understanding. "I feel more secure now that he'll take care of me," she says.

These days, McGowin also draws emotional support from Richard Badessa, 58, who left his position as a professor of English literature at the University of Louisville in 1991 when, he says, "I realized I was not quite with it. and my students knew it." The two met after McGowin contacted the local chapter o( the Alzheimer's Association and asked to set up a support group for early-onset victims. "I fell it I didn't find someone else out there like me," she says, "I would end up like [Janet Adkins] the 54-year-old woman [with Alzheimer's] who was the first to use Jack Kevorkian's suicide machine."

Badessa was the first patient to join the group. At the time, recalls McGowin, his disposition was worse than resigned. "He was steeped in Marcus Aurelius, the stoic of all time," she says. "His attitude was, 'I'm gonna die.' " Now, says Badessa, who lives in nearby Dellona, Fla., with his sister. McGowin "has made me see how life can be lived rather than endured."

Despite their superficial differences—"he likes classical music, I like Patsy Cline," says McGowin—Richard and Diana meet often for trips to art museums, support groups and long talks that, she says, "make us feel human again." Apart from her marriage, all that keeps them from driving into the sunset together, Diana says with a laugh, "is that we couldn't find our way back."