Grandma Kurnitz comes across as a monster -- a stern, cane-wielding Teutonic tyrant who inspires fear in her children and terror in her grandchildren.

But she's not a monster to Mercedes McCambridge, who portrays her in Neil Simon's "Lost in Yonkers," which begins a month-long run at the Mechanic Theatre Tuesday. "Ultimately," McCambridge claims, "Grandma is a hero of mine."

Of course, you say. After all, this is the actress who was the voice of the demon in the movie "The Exorcist."

Monsters 'R Her.

But that's not it at all, McCambridge protests. For starters, she refuses to label any of her characters "heavies." "People call them heavies. I don't believe I ever played a heavy -- Lucifer himself. He was the prince of heaven and blew it and ended up where he is. But I'll bet you anything that in the real dark night of the soul, where it's always 3 o'clock in the morning, according to F. Scott Fitzgerald, I'll bet you that Lucifer cries."

As to tough-spirited Grandma Kurnitz -- the pivotal character in this 1991 Pulitzer Prize-winning drama about two boys sent to live with their grandmother during World War II -- McCambridge explains, "My grandmother was like that; so was my mother. I feel that the people who pushed me the most, including the teachers, are the ones who made the greatest impression on me and loved me the most."

Unlike Irene Worth, who originated the role but admitted she neither liked nor admired the character, McCambridge -- who replaced Worth on Broadway -- admires Grandma's honesty and adherence to principle. And, she says, "I also know, in my experience, that the people who seem to be the coldest turn out to be the most vulnerable."

Speaking from the show's stop in Sarasota, Fla., McCambridge enumerates a "Who's Who"-sounding list of examples -- Orson Welles, James Dean, Eleanor Roosevelt, Adlai Stevenson and Billy Rose, all of whom figure into her 1981 autobiography, "The Quality of Mercy."

And then, reflecting further on the tendency to conceal vulnerability beneath a formidable exterior, the 73-year-old actress pauses and adds, "I do a great deal of it myself to protect myself. False protection."

She quotes a line of Grandma's she feels is key: "You want to hear what my truth is? . . . Everything hurts. Whatever it is you get good in life, you also lose something."

Although McCambridge prefers not to talk about it, she alludes to what she calls "a Euripides tragedy" in her life. In 1987, her son murdered his wife and two daughters and then committed suicide.

"Sometimes people have said to me, 'How can you live?' I can't live with it, but the thing is, I got up this morning, and today looks pretty good, and that's how I don't live with it because you can't live with it. Nobody can live with it, but you do," she says softly.

"I rely very heavily on what I read, and Marcus Aurelius is one of my favorites. He says that nothing outside myself could injure me without my permission. If that's true, I've done an awful lot of damage to myself, and to continue along that line, I'd have to be crazy."

McCambridge was in semi-retirement in La Jolla, Calif., when she decided to audition for Neil Simon. Most actresses would refuse to audition at her point in her career -- her credits include an Academy Award for "All the King's Men" and starring roles in the Broadway production of "Who's Afraid of Virginia Woolf?" and the national tours of "Agnes of God" and " 'night, Mother." But she swallowed her pride and told herself, "Let's just see if you are big enough to walk into this room and meet this man you've never met and impress this man as if you were 16 years old." And with the enthusiasm of a teenager, she exclaims, "And I did! Only took about 15 minutes."

The truth is, McCambridge has rarely had to audition for anything. Instead, show business came to her. The Illinois native was an undergraduate at Mundelein College in Chicago when an NBC executive saw her perform and signed her to a five-year radio contract. In Chicago -- a hub of radio activity in those days -- and subsequently in New York, she played characters ranging from a little boy to the title role in "Abie's Irish Rose."

Even now, though she's hesitant to pick favorites, she admits she prefers radio to any other medium. In fact, her love of radio was what attracted her to "The Exorcist." "At the very base of it was the conviction that this is a radio performance in a film," she explains.

Still, due to her strict Catholic upbringing, she harbored some concerns about portraying the voice of the devil. She expressed these concerns to the late Rev. Gilbert V. Hartke, founder of the drama department at Washington's Catholic University, where she had served as artist-in-residence. "He said, 'If you took on all the attributes of every character you played, you'd be an inmate, not an actress,' " she recalls.

So her conscience was clear as she embarked on one of her most grueling assignments. She describes her technique in her autobiography: "When I felt I was ready to go for a 'take,' I would load my mouth with apple sections, munching them to a not-quite-mealy consistency; and then, from a paper cup, I would add, in my distended mouth, two eggs -- yolk and gluey stuff. At the instant before the pea soup and cornflakes erupted on the screen, I would swallow the glob I'd been holding, down to mid-gullet, flex my diaphragm muscles, and gag it up onto the nest of microphones!"

Despite this virtuoso performance, when the movie came out, McCambridge's name wasn't in the credits. "[Director] Billy Friedkin thought maybe people would believe that the devil himself was playing it," she says now. However, McCambridge raised a devil of a fuss, and after the first 26 prints, her name was there.

McCambridge had acquired some clout by 1973, the year "The Exorcist" was released; things were tougher when she started out. In 1944, she was fired from what would have been her Broadway debut, "The Hasty Heart," after nine days of rehearsals. In her next show, "Hope for the Best" -- co-starring Franchot Tone -- she made it to the Washington tryout when one of the producers decided "Nobody would believe Franchot Tone would fall in love with anyone who looked like me," she recalls.

McCambridge had been scheduled to come to Baltimore in "Hope for the Best." Instead, she came here a year later in "Twilight Bar," which closed in Philadelphia, its next stop.

The actress made several trips to Baltimore in the 1970s to lecture on alcoholism -- a subject that brought her national attention when she testified before a Senate subcommittee in 1969. One of the first celebrities to go public on this issue, McCambridge no longer serves as a spokeswoman. But her impact is still being felt.

"There was a letter for me last night at the theater with two white roses from a woman who said she heard me on television in the early 1970s," McCambridge says. "She wanted me to know she has just celebrated her 21st year of sobriety. She said, 'I thank you for resurrecting my life.' I didn't. I just happened to be where she heard me.

"I don't know that I'm strong enough or well enough suited to be in that position, but in this case it certainly worked out well. My dresser said, 'You know how many times you've opened letters like that?' "

Chances are, there will be more letters as "Lost in Yonkers" travels to cities including Pittsburgh, Detroit, Dallas, San Francisco and Los Angeles. This might seem a taxing schedule for a woman in her 70s, but McCambridge loves it.

Although the weather is inclement in Sarasota on the day of this interview, she can see her fellow cast members playing pingpong from her hotel window. "They're all out there on this gray day with their spirits high, pretending they're enjoying a beautiful day," she says. "It's wonderful to see them out there. They are a family, and I am part of it."