As the curtain rises on the Broadway drama The Petition, a white-haired woman, still beautiful in the autumn of her life, is reading serenely in a genteel English parlor. Only a few seconds earlier Jessica Tandy was quelling the familiar "fear in my gut" that she always feels until the magic of an audience chases it away. Sitting nearby, Hume Cronyn, her husband offstage and on, digs his elbows into the arms of his chair so that the newspaper he is holding will not visibly rustle in his shaking hands. Later, at intermission or after the show, the two stars will begin their ritual whisperings: his pauses are too long; she's not showing enough emotion. "We're each other's strongest critics," says Tandy. "And biggest supporters," adds her spouse.

For 43 years of intensely interdependent married life, the pair has confronted perennial stage fright, quavering hands and thunderous ovations—all of which seem to intensify with the years. She is 76, he 74. Though each has had many individual triumphs, it is the impact of the Tandy-Cronyn presence on a stage without other actors that electrifies playgoers. From their first Broadway appearance together in the hit The Fourposter in 1951 to The Gin Game in 1977 and now The Petition, they have presented themselves to audiences alternately' as loving and self-sacrificing, cantankerous and selfish. On the American stage, no other couple since the Lunts has depicted so well the fragile fabric of married life.

The pressures of playing in a "two-hander," as the Cronyns call these appearances, are so intense that they are now threatening to make The Petition their last theatrical duet. "To have all the responsibility on these four shoulders is a heavy load," says Tandy. "There's no time for a personal life, and neither of us wants to keep on working all the time." Besides, she adds, "who knows how much time we have left?"

Cronyn's performance as a fussy, retired English general won him a Tony nomination, and Tandy was nominated for her portrayal of a liberal-minded gentlewoman harboring a sad secret. The critics of course loved the stars, but they attacked the show ("A high-minded television sketch padded out to two acts," said the New York Times). Tandy refuses to read the notices. "It may sound snotty, though it's not meant to be, but no matter what is written," she explains, "I have to go on every night and believe what I'm doing. If they say Jessica Tandy can't act her way out of a paper bag, I don't want to know that because I've got to act my way out of a paper bag!"

Cronyn, always the more outspoken of the two, has this message for the critics: "The ones who say, 'What a pity the Cronyns can't find something worthy of their talents,' get me outraged. How often does a play come along for people in their 70's that is poetic, of real distinction and of topical significance? Come off it! If you're a working actor, you do what comes along and hope to make the best of it."

Cronyn tamps down his pipe with vehemence as he speaks, and Tandy looks resigned. She disapproves of his smoking, though not necessarily of his frank, at times curmudgeonly manner. Sitting beside her husband in the Manhattan hotel suite where they have lived since 1980, she is gracious and rather deferential to Hume. "She is, after all, English from the Edwardian tradition," says their daughter, actress Tandy Cronyn. "It's a cultural thing."

More than that, Jessie, as Hume calls her, regularly coddles her spouse, fixing him smoked salmon and custard after the show "so he'll have something in his tummy." Cronyn appears to delight in his wife's attentions. "To try and stand outside the marriage, I'd say we have complementary capabilities," he reflects. "I do the hustling and the business. I do more script reading. I handle contracts."

The formula appears to work. Moreover, they do not compete with one another. "How can I be jealous of Hume?" asks Tandy. "He can't play my parts, and I can't play his. Yes, I suppose there have been times when one or the other is doing better on the surface, but it just doesn't bother us." Says Hume: "If Jessie has a triumph, I feel, quite irrationally, that it's mine. Or when I read that she is beautiful, I feel wonderful. She's mine." His wife blushes slightly, and the couple exchanges a glance that for a split second cuts out the rest of the world.

Yet the marriage has had its strains. Once, during The Gin Game, Cronyn moved out for a few days. "We weren't quarreling," he explains. "We needed space." Even now they are protective of their individual privacy. "That's Jessie's room," says Cronyn, gesturing toward one end of their two-bedroom quarters. Pointing to the other side, he explains, "That's my room, though I sleep [in Jessie's room] quite a lot when she'll have me. Ask a lawyer or a plumber or any of those people how they'd like to share the breakfast table and the lunch table and the office with their spouse or hand each other tools. It can get very rough."

Tandy carefully plucks a dying flower out of an arrangement on the coffee table, then summons the memory of Sybil Thorndike to emphasize Hume's point: Dame Sybil, she explains, was once asked if she had ever contemplated divorce. "Divorce?" she replied. "Never! Murder? Frequently!" And that, says Tandy, "is absolutely right for us."

Tandy's devotion to the words of theatrical greats like Thorndike began in her childhood in London. Her father, a minor executive in a rope company, died of cancer when she was 12. Her mother, a headmistress in a school for retarded children, considered the few pence it cost to go to the theater in the '20s money well spent. In 1924 Tandy enrolled in the Ben Greet Academy of Acting in London. Three years later she began doing repertory work and in 1932, at age 23, caused a sensation on the London stage as an impetuous schoolgirl in Children in Uniform. That same year, she married the British actor Jack Hawkins.

In 1940, with their 6-year-old daughter, Susan, in tow, Tandy arrived in New York to appear on Broadway in Jupiter Laughs. One night a nattily dressed young man with jug ears and a persistent nature came backstage to greet another cast member. There he was introduced to Tandy.

Hume Cronyn was by this time an established stage actor, a profession for which he was hardly groomed. His father, Hume Blake Cronyn, was a member of the Canadian Parliament; his mother was Frances Amelia Labatt of the brewing family. Growing up in Woodfield, an Edwardian mansion in London, Ontario, he was raised by nannies and servants. Later, at McGill University, he got involved in student acting groups and found a life in the theater far more enticing than his planned path of law. Leaving McGill after a year, Cronyn arrived in New York in 1932 to attend the American Academy of Dramatic Arts. By the time he wandered backstage and met Tandy in 1940, he had married and divorced a fellow drama student and had made his Broadway debut in Hipper's Holiday in 1934.

On the surface neither was in the position for a relationship. Though Tandy's marriage to Hawkins was not a happy one, she considered divorce "a disgrace, an admission that you hadn't made it work." Cronyn was engaged to another actress. Still, he was smitten by Tandy and relentlessly wooed her, showing up at her door in top hat and tails for nights on the town. "He kept bringing up the subject of marriage," recalls Jessie, who finally got a divorce in 1942 and promptly said yes to Hume.

The newlyweds settled in Hollywood, where Cronyn was under contract to MGM and Tandy to Fox. Their first film together was The Seventh Cross in 1944 with Spencer Tracy. Even then, Hume was outspoken and known for his obsession with detail. "The-son-of-a-bitch," Tracy once commented, "would fix the damned lights if they'd let him."

Over the years came their two children—Christopher, now 43, and Tandy, 41—as well as a succession of houses in California and New York and careers that eventually focused more on stage than screen. She won her first Tony in 1948 for her performance as Blanche DuBois in A Streetcar Named Desire and pulled in two more for The Gin Game and Foxfire in 1983. He won an Academy Award nomination for The Seventh Cross and a Tony in 1964 as Polonius in Richard Burton's Hamlet. For both, taking minor roles in films like The World According to Garp and Cocoon has helped finance holidays and real estate (they once owned a vacation retreat in the Bahamas).

Inevitably a career of such longevity has had its bleak side. In 1969 Hume lost an eye to cancer. Fitted with a glass eye, he had to readjust to seeing the stage, and the world, through his good one. Earlier in the '50s he says, "Jessie decided she was a lousy actress, a lousy wife and a lousy mother. I went back to our scrapbooks and pulled out reviews and said: 'Will you listen to this?' I also told her: 'Look, I'm married to you, and I think I'm very blessed, and I won't hear this garbage about your inadequacies.' " Even now, Tandy seems troubled at the mention of those times. "I felt very guilty working," she says. "There were all those pulls—the husband, the children, the career. How would I keep things on an even keel?"

Their children, Cronyn fears, may also have had rough times, but more from his own self-described "rigid-ness" than from their parents' careers. "I'm a taskmaster. I was brought up that way, and I'm sure I imposed that on my kids." Suddenly he is defensive. "Look," he continues, "you do the bloody well best you can. You fumble. You make mistakes."

Christopher Cronyn, a film production manager who worked on Richard Pryor's movie Critical Condition, to be released next year, chooses not to discuss his parents. His sister, Tandy, who acts primarily in repertory theater, confirms that her upbringing was strict but not necessarily unpleasant. "I used to be shocked when I went to friends' houses to see kids talking back or being rude," she says. "None of that was allowed for me, but I don't regret any of it."

Now edging toward their ninth decade, the parents show little sign of lessening their demanding standards—at least in professional terms. Cronyn has co-authored a screenplay based on Anne Tyler's 1982 novel Dinner at the Homesick Restaurant and hopes to see it produced. After the scheduled run of The Petition ends in October, Cronyn and Tandy will co-star in a TV version of Foxfire, to air in 1987. Then Tandy yearns for a respite. A grandmother of four and great-grandmother of two by her daughter Susan, she wants time for her family, for travel and for the hobbies she never had. "Who knows? Maybe I will make pottery. I want to keep busy."

Meanwhile, offstage as on, the two actors maintain their impecccably timed dialogue. Tandy begins to tell a story about Dame Peggy Ashcroft.

"Oh, can I tell it?" interjects Cronyn with an eager grin.

"Oh, all right," sighs his wife, who then waggles her finger at him and warns: "But get it right."