In a period of relatively scarce major studio production and inflated admission prices (no doubt one encourages the other), it would be disservice to overrate an appealing but slight entertainment like Martin Brest's "Going in Style," opening today at area theaters. Audiences may grow fond of the film's peculiarly haunting yet fragile comic pathos if they feel free to discover it themselves. Going in with big expectations is almost certain to invite a letdown. Of course, the problem with $5 movies and $20 plays is that a crippling burden of proof has begun to descend on every single show.

"Going in Style" is a geriatric tragi-comedy about three vegetating pensioners -- George Burns, Art Carney and Lee Strasberg -- who share an apartment in Astoria, Queens, and decide to change their docile routine by sticking up a bank. It's an offbeat caper film, propelled by a gimmicky, improbable, treacherously 'cute" premise but preoccupied with the character traits and fundamental loneliness of the unlikely crooks.

As the trio's ringleader and agitator, a retired salesman named Joe, Burns has his best movie role yet and responds with far and away his strongest performance. It's the kind of old man's role -- tough, subtle, dignified, resolutely unsentimental -- that he might have been waiting to test himself with after the easy saccharin pickings of "Oh God!" and "Just You and Me, Kid." Burns has no opportunity to act smugly ingratiating in "Going in Style," and it becomes him to be all seriously comic business for a change. An adorable facade gives way to an authentic characterization of a resilent old man, physically frail and diminutive but iron-willed, keen-witted and effectively devious.

The caper itself seems a flimsy and perhaps unacceptable pretext for the character interplay and revelations that grow out of it. One wishes Brest had invented a less familiar device for introducing us to the old men. The plot could also ramify more dramatically than it does in the aftermath of the bank job. Bret's storytelling powers seemed better developed in his astonishing student feature, "Hot Tomorrows," in which the plot twists were awesomely audacious but also logical.

"Going in Style" is constructed on a pretty thin dramatic surface. Drawn in by the intimate mood and the affecting performances of the three principals, one tends to make allowances for the plot artifices in order to savor the comic accuracy of certain behavioral detials and the emotional resonance of certain vignettes.

Many of us excited to superlatives by "Hot Tommorws" are bound to have mixed feelings about "Going in Style." The latter isn't nearly as impressive or surprising, but it probably didn't emerge out of a creative need as desperate, perhaps desperate to the point of precocious genius. At the same time, it's a relief to see that Brest, only 28, hasn't blown his first opportunity at a major-studio, mass-audience attraction. "Going in Style" is cautiously conceived, but it also projects a sincere human interest and reveals a command of intimate, subtle dramatization that is likely to prove Brest's artistic and commerical fortune sooner or later.

For example, Strasberg and Burns excel in remarkable scenes that reveal old memories coming back to haunt their characters with a sentimental impact that makes them feel miserable and humiliated. Strasberg can't sleep for the recollection of some distant outbreak of paternal anger that caused him to scold his son. Burns gets down a cardboard box filled with old photos, and it takes only a few seconds of browsing to have him regretting this nostalgic impulse.

There's only startling, sustained composition that recalls the mood of lyric pathos Brest achieved in "Hot Tommorrows": One of the characters is stricken with a coronary while sitting quietly on a park bench with his friends; it's a sweltering summer day, and in the foreground children dart through the spray of a hose.

Brest's astuteness is also evident in the casting and acting, consistently right from leads to bit players. In supporting roles Charles Hallahan is particularly good as Carney's beef, decent nephew, a hard-working young family man chosen by the old men as a likely beneficiary of their ill-gotten gains. Karen Montgomery makes the most of perhaps 30 charming seconds as a comely hooker who pantomimes a fleeting invitation to Carney in a Las Vegas casino.

Martin Brest has a lot on the ball, a lot of potential satisfaction to offer American moviegoers in the '80s. But to be on the safe side, think of "Going in Style" as more of a promising exhibition than a major, championship event.