Some label them "today's Lunts," but that's inaccurate Life never repeats exactly.

The similarities between the careers of Hume Cronyn and Jessica Tandy and of Alfred Lunt and Lynn Fontanne are limited. Like the Lunts, the Cronyns have had a long marriage and costarring career, and like the Lints the Cronyns always give impeccable performances. But, unlike the Lunts, the Cronyns have had separate careers and have reached into films and TV.

Presently the Cronyns are dazzling Broadway in "The Gin Game," D. L. Coburn's two-character study of strangers who meet in a senior citizens' home. It is one of the few two-character works that didn't give me the itch to leave. Their performances, which call for them to play 14 hands of gin rummy, are a tour de force.

If there's any justice, the top Tony acting awards this spring will go to the Cronyns, both as a team and for their striking, individual performances. Each has won an individual Tony, Tandy for her 1947 creation of Blanche in "A Streetcar Named Desire" and Cronyn for his Polonius in the Richard Burton "Hamlet" of 1964.

They collected a half-dozen major acting honors for another two-character play, Jan de Hartog's "The Fourposter," but the Tony eluded them in that one. They performed for four years in that 1951 study of marriage, which tried out at Olney and closed four years later at the National. But that play did lead them to their most popular TV series, "The Marriage."

What astounds one about the acting Cronyns is the huge range and depth of their credits. Tandy's Blanche set the standard for all to follow. Her subsequent London counterpart, Vivien Leigh, landed the film version and, hence the lasting image, but it was Tandy's silvery voice that first quickened listerners to that memorable line: "I have always depended on the kindness of strangers."

She's also acted in farces, detective yarns and Shakespeare. She and Cronyn spent two recent seasons travelling around America in three plays by Beckett, and I truthfully can say I never have seen Tandy give anything but a searingly believable performance.

The first time I saw her she was leading lady to Paul Muni in a National Theater tryout of Emlyn Williams' "Yesterday's Magic," a drama about an old actor's attempt at a comeback. His chief booster was his club-footed daughter, played by Tandy.

That was in 1942, and I waited at the stage door for glimpse of this English actress, new to me though not to New York where she'd appeared for two brief runs. I almost wept with relief when I saw her spritely walk. That stage limp was merely her acting technique.

Now at New York's John Golden Theater one watched Tandy's Fonsia slump on stage in a dreary housecoat and slippers, the epitome of dowdiness. In the course of the four scenes she brightens up considerably as she learns how to play gin with such ease that she carries on irrelevant conversation continously with the angry old man she has just met. Their iconoclastic spirits are united in sneering at their new home and associates. Cronyn's irascibility sets up a string of reactions for Tandy.

In one scene in particular, the Tandy technique wholly eluded me. Often, at a remove, one can analyze how an effect is created. Here I couldn't. With a pillow at her back against the chair, she sits facing Cronyn, never moving. Her hands and body are utterly still, her face immobile. Yet she takes us inside her mind, conveying just what she thinks of this quirky man who ultimately will give her the shock of her life. She senses a good deal about him, all sorts of accurate detail. But she does not foresee where their relationship will take them. In this, Tandy implies why Fonaia's life has been a failure.

This maze of a life's history is conveyed without a line, without a reaction, yet the thought and its implications transfer infallibly to the audience.In their dressing room, I asked the anything but dowdy Mrs. Cronyn how on earth she did it.

What I was given was that silvery, youthful chuckel and:

"I don't know about all that, but I do know that after learning this part, those Beckett monologues are child's play. Here the concentration is so divided between the lines and thought we have and those damned games we play. We have to play a reasonably honest game each hand and we have to know which of the 14 games we're in. And we're aware that those people in the front of the balcony probably can see the cards we have.

"The split concentration is the challenge and, by the nature of cards, even the cards we use, every performance is different."

Her husband explains: "Yes, the deck is stacked but it can be stacked only to a certain degree. We've made up a deck that consists of four aces, four deuces, two sixes, five sevens, five eights, six nines, six tens and 20 face cards, 52 in all.

"There are cues for the card, particularly a seven of clubs for me, a queen for Jess at exact times.

"Of course, while the chances are better than with a true deck, the card doesn't always come up on cue and we have to convince the audience that it does. We just have to fake it. Quickly. Very quickly. It has to be just right at the end of the scene where Jess cries 'Gin!' There's also the temptation on play the cards we do draw for real, but that would demolish the script.Mike Nichols, our director, was both patient and creative.Sure, we practiced at home. But the actual concentration each game; to keep them straight, is sheer, bloody hell."

While all this is going on, the Cronyns are creating through Coburn's hilarious lines and situations two very true, even pathetic people. Under the audience's roars of laughter is an intense sense of involvement. We know this man, this woman.

The Cronyns always have been immensely professional about their work, planning seasons in advance and setting aside blocks of time, say, for Canada's Stratford Festival or his producing activities. They'll take a holiday from "The Gin Game" in June, rest a month, then give Hume Cronyn a month for a project he plans for 1980. In September; they'll set out on a national tour that will bring them to Washington a year from now.

Both are London-born but of different Londons, his Ontario's, here England. Both are in their late 60s.

Hume studied with Harald Kreutzberg and made his professional bow at Washington's National Theater in Steve Cochran's Stock Company of 1931 in "Up Pops the Devil." Four years later he headed the touring company return of "Three Men a Horse" on the same stage. He acted Hamlet for Robert Porterfield's Barter Theater in the 1940s, its Polonius with Burton in the '60s. His first movie, "The Seventh Cros," brought him an Oscar nomination.

Tandy's Shakespearean parts total more than those of any living actress, including Ophelia to John Gielgud's Hamlet in England, Denmark and the U.S.S.R., and Getrude at the Tyrone Guthrie in Minneapolis, where the Cronyns spent two full seasons as the first of the stat professionals to perceive the importance of regional theater. Tandy's films have ranged from "The Valley of Decision" and "Forever Amber" to "The Birds" and "Butley." After trying acting, the Cronyns' daughter and son are both in the production side of theater and TV.

To detail their careers would take pages; but to perceive the fruits of their acting careers, the few hours of "The Gin Game" is proof enough that the Cronyns are brilliant masters of their elusive, disciplined art. It's a marvelous eveniing of perfectly joined performances.