LEBANON, N.H.--Susan Lacey's deepening depression began casting its shadow over her husband and teen-age son late last summer. But her 9-year-old daughter, whose artistic personality so resembled her own, had been affected the most.

"I kept trying to reassure her," Susan said. "Yet by October, I was no longer sure, and I couldn't lie to her. I've never lied to her.

"And I finally found myself saying to my husband, 'I can't tell her anymore that things are going to be OK.' I said, 'I never could understand how this could happen before, but I'm very suicidal right now and I know that if I kill myself, how could you ever say to her that things are OK again?'

"And I said to him, 'I think I have to kill her first. Then I'd kill myself.' And I was barely able to breathe as I was saying these things, and yet I believed that was the course I was going to have to follow."

That was what brought 41-year-old Susan Lacey to Dartmouth-Hitchcock Medical Center in Lebanon, N.H., two days later to undergo the most feared and reviled treatment in psychiatry: electroconvulsive therapy.

Shock treatment.

It sounds like something out of psychiatry's Dark Ages, reminiscent of leeches and lobotomies. Never more so than in this era of Prozac, when pills can change personalities overnight.

But for reasons that have eluded scientists for 60 years, there remains no faster, safer way to yank people out of deadly depressions than by placing electrodes on their temples and zapping their brains with enough electricity to trigger convulsions.

As a result, ECT--psychiatry's oldest continuously used procedure--is quietly making a comeback as the treatment of choice for the dangerously depressed. This year, an estimated 60,000 Americans will undergo a total of a million ECT sessions, the most since the mid-'70s. Nearly all will get better, at least for a while.

Most will be white, middle-class people, a growing number of whom will be treated in the morning and sent home in time for lunch. A few will be given ECT for schizophrenia or catatonia. But the vast majority will be severely depressed men and women for whom antidepressant drugs work too slowly or not at all. Some can't take them for other reasons--heart conditions or pregnancy.

In 10 years of battling depression, ECT was the one treatment Susan Lacey hadn't tried. She'd been through psychotherapy, bright lights, mood stabilizers, antidepressants. And she'd suffered through countless side effects: weight gains, headaches, appetite loss, sexual dysfunction, insomnia.

An award-winning author of scholarly magazine articles and books, Susan once described herself as "a high-energy perfectionist with a great sense of humor, physically active, very engaged with my children and various organizations, an irrepressible reader, and a highly motivated writer."

That was the old Susan, before the illness had crowded everything else from her life. She resigned the boards she had served on--the arts council, the historical society. Last year, unable to meet her own exacting standards, she'd given up even trying to write.

Winters were the worst. The short, cold days and long, dark nights heightened her feelings of despair. But last summer, in place of the usual respite, Susan felt herself going further downhill.

Her migraines got worse and her crying jags lasted longer. Her head hurt so much she could no longer listen to her daughter's piano playing. She stopped helping her son with his homework when she realized she could no longer read.

"I mostly asked my children just to leave me alone. I left most of the housework to my husband, who now had to make all the dinners and do all the laundry."

Her blue eyes turned red and swollen from crying and lack of sleep, and her face grew slack, as though the muscles no longer worked. No longer eloquent, she spoke in a weary monotone that seemed to come from far away, groping for words like someone speaking a foreign language.

She began showing up for therapy sessions with questions about bullets and guns. Sleep topped a growing list of things she'd forgotten how to do. At night, while her family slept, she sat in the bathroom and cried.

Mornings, she sat by the river that flows past her house, immersed in thoughts of slicing her throat with her penknife and throwing herself in the water. It wouldn't be hard. "There was virtually nothing left of me."

Still, when her doctor recommended ECT, Susan was horrified.

"I knew that the illness was killing me," she said. Yet she was afraid of ECT's effect on her brain, that while "it might save my life physically, it might not return me to the person I'd been."

Such fears are common in light of ECT's history, said Dr. Matthew Rudorfer, assistant chief of the Clinical Treatment Research Branch of the National Institute of Mental Health in Bethesda, Md.

Shock therapy began in the 1930s, when an Italian scientist used electricity to induce a seizure, refining a concept that goes back to the 19th Century, when one approach was to put electric eels on patients' heads.

In 1939, the New York State Psychiatric Institute at Columbia-Presbyterian Medical Center introduced shock therapy to America. It soon became psychiatry's biggest fad, used to treat virtually everything.

There was, after all, nothing else.

"This was the era of the large state hospital, where people stayed sometimes for their lives," Rudorfer said. "What else were they offered? Ten types of water treatments or massages."