WIDOWED By Dr. Joyce Brothers (Simon & Schuster: $19.95; 256 pp.) . You have to admire Dr. Joyce Brothers for what she's tried to do--take her private pain at the death of her beloved husband Milt and turn it into some public good. She seems to understand that she possesses a unique, ironic power. For a psychologist who has spent her professional life doling out the answers to admit that she has none, that she is as vulnerable as the next person, makes her story all the more poignant. If as emotionally functional a being as Joyce Brothers is incapacitated by grief, then merely mortal readers in the same sad situation are to be absolved if they cave in; if she struggles to find the path back, she inspires them to do the same. She is disarmingly frank at every stage of the grim game: As her husband's disease progressed, she became obsessed with her pending loss--to the extent that she ignored her daughter's very real grief. As a new widow, she foundered in self-pity--some of it overblown, some of it the quite reasonable response to a couples-only culture that suddenly had no use for her. A bereaved spouse will likely find solace here. What he or she will not find enough of, finally, is substance. Brothers has spent much of her career perfecting the 60-second sound bite, which is not the proper discipline for the book writer. She tends to repeat key phrases and snippets of advice; one wishes she had counseled a bit less and delved just a bit more.