Question that could be taken up at a night class foe adult students of professional comedy:

Why are probings to find out "What Is Humor?" so tragic, while discussions of, say "What Is Love?" usually turn out to be funny?

There is such a class for apprentice comics in the British play "Comedians," now at Arena Stage's Kreeger Theater, and the question of what makes comedy is taken up with skill and depth, bitterness and philosophy, but with only the most chilling humor.

Two old comedians go after six aspiring ones from opposing sides. The idealistic academic's belief that comedy is society's medicine, of which the main ingredient is truth, is set in opposition to the practical employer's viewpoint that comedy is society's drug, which makes people feel good by clouding the truth.

Assembling in an appropriately dreary classroom, with their dripping umbrellas and grim ambitions, the apprentice comedians, working-class people in the traditionally unfunny industrial city of Manchester, fight it out. Their teacher argues against the easy joke based on prejudice - "That's a joke that hates women," he surprisingly admonishes a pupil. Their possible agent to success argues against the jokes based on social critism - "Get some distance, don't give us your hang-ups straight."

Some of the students betray their teacher by reverting to the familiar vocabulary of Irish, Jewish and women jokes; another strikes out with a perfectly stylized, and quite unsuccessful, attack on the upper classes. There is effective acting here, because the comedians are stripping this humor of its professional gloss and thus giving it to us fully exposed.

But in the end, it is neither brand of comedy that wins our laughter, but a simple joke based on the same principle that makes analyses of love so often funny - the discrepancy between humanity's grand pretentions of perfection and the simple human condition.

In a preview performance, the audience was not laughing much during the demonstrations of night club routines, and what giggles there were for the television-level-humor-gone-raunchy sounded somewhat apologetic. Being forced to examine what we usually laugh at easily - the remarkable presence of the teacher, strongly and subtly played by Robert Prosky, as he sits critically and unsmilingly through the routines - is responsible for that: We are Shaken up and therefore not amused.

But "Comedians," after all, is not a comedy.