"Fire Sale," at the area theaters, has quickly supplanted "Jabberwocky" as the unfunniest movie comedy in town. This boorish, domestic farce was written by the incorrigible Robert Klane, who sold "Where's Poppa?" to the same producer, Marvin Worth, back in 1970. Worth is best known as the producer who helped sanitize the character of his old client. Lenny Bruce, for the sanctimonious "Lenny."

Sort of a poor man's Terry Southern. Klane has reemerged as a screen-writer after several years of conventional TV comedy hacking. "Fire Sale" finds him brandishing the same ugly shtik at unsuspecting movie-goers; grotesque situation comedy about crazed Jewish parents and children animated by naked hostility and vindictiveness rather than satirical perception or adroitness.

In "Where's Poppa?" George Segal and Ron Leibman were cast as the frustrated, manic son; of a dotty old widowed mother, Ruth Gordon. In "Fire Sale" Alan Arkin and Rob Reiner play blithering brothers, tyrannized into incompetence and impotence by their brusque, insulting father. Vincent Gardenia, a disreputable retailer plotting to collect on the fire insurance for his money-losing department store.

Carl Reiner's direction of the romantic interludes between Segal and Trish Van Devere gave "Where's Poppa?" a mitigating split personality; the film was alternately leguiling and overbearing. Arkin has directed "Fire Sale" without modulation. The nut-cast humor is unrelieved: one screaming, foaming-at-the-mouth, brutalizing joke or situation succeeds another.

Klane's level of sick facetiousness may be best illustrated by the character of Uncle Sherman, Gardenia's brother-in-law, played by Sid Caesar one is grieved to report. Uncle Sherman lives at a mental institution and fantasizes growing back the leg he lost in combat in World War II. Before leaving on vacation his sister, Kay Medford drops by to leave him a present - one roller skate - while his brother-in-law urges him to commit arson, on the pretext that burning the store is an Allied commando mission.

Caesar's big pantomime opportunity involves nodding off while trying to pour gasoline into bottles. Naturally, he sloshes gas all over himself. Then he starts lighting matches for the payoff, which requires us to believe that Uncle Sherman blows up his room but not himself. In a similar respect, Gardenia's character is put in a coma for a while to accommodate a series of predictable gags built around the abuse of his helpless, inert body, then revived when the filmmakers have exhausted that premise.

Klane certainly acquired a monstrous, self-defeating streak of hostility somewhere along the line. His joke aren't funny; their cruelty and heartlessness just affront you, demanding total capitulation or rejection.

It's impossible for any performers to flourish in such a humiliating context, but some can be more humiliated than others. In "Fire Sale" it's Rob Reiner, cast as a big, pallid, wheezing weakling. "There are certain shades of limelight that can ruin a girl's complexion," said Holly Golightly. Reiner has stepped into a role that could make him persona non grata on the screen forever after. Compared to Reiner, the big wimpy type of a generation ago. Grady Sutton, a frequent butt of W. C. Fields' humor, seems like a real catch and an expert comedian.