Circle Rep's wildly funny broadside; The Great Grandson of Jedediah Kohler; Comedy by John Bishop. Directed by John Bard Manulis and Marshall W. Mason.

The Circle Repertory Company has fired off a wildly funny broadside of comic iconoclasm. John Bishop's ''The Great Grandson of Jedediah Kohler'' is part pop-culture cartoon, part surreal satire, and part mock tribute to the men who made the west a la Hollywood.

The playfulness begins when Death, in the less-than-sinister person of Jake Dengel, forecasts a bad end for Jed Kohler (Michael Ayr), a rising young ad man employed by Creative Ideas Inc. Early on, Jed discovers that there is something missing in a life spent shuttling between Madison Avenue and suburbia, with occasional junkets to Detroit for industrial shows and infidelity.

There seems to be more than a triple generation gap between Jed and his legendary forebear, Jedediah (Edward Seamon), the frontier marshal who won the shoot-out at Oak Street Corral and who has been played on the screen by the likes of John Wayne, Charles Bronson, and Henry Fonda. Jed's wife (Trish Hawkins) and his girlfriend (Katherine Cortez) walk out on him simultaneously while Jed loses his choice office and is reduced to the role of ''gofer'' at the ad agency. End of Act I.

The second half of the evening reveals how the still friendly wife, now a member of the zealous Earthwatchers, persuades Jed to help her and fellow environmentalists expose the lethal qualities of the amphibious luxury vehicle Jed's agency is publicizing. The latter-day showdown occurs at the great Las Vegas dealership extravaganza where the Espray is to be introduced. The showdown pits the engineer (William Hurt), who knows all the damaging secrets, against security guards led by a company cop who is the spittin' image of the great Jedediah (one of Mr. Bishop's little ironies).

If all of this sounds wackily far out, events on the stage of the Entermedia Theater more than confirm the impression. For Mr. Bishop and his collaborators have created a lampoon on the grand scale, a catch-all comic-notions counter that offers everything from Jed's Vietnam veteran brother (Jimmie Ray Weeks), who tells shaggy-war stories, and the Mister Malaprop of Madison Avenue (Ken Kliban) to a college athletic coach (Jack Davidson), who is every inch a pro when it comes to negotiating endorsement deals.

If a few of Mr. Bishop's gags seem somewhat overworked, the good news is that so many of them are in such nifty working order. Furthermore ''The Great Grandson of Jedediah Kohler'' gets better as it progresses. The intricate production, with its rapid continuum of scene changes and flashbacks, has been expertly assembled and ordered by co-directors John Bard Manulis and Marshall W. Mason. The Circle Rep Company, whose members sometimes play more than one role, is in fine comic fettle.

The action fills all of the large Entermedia stage and sometimes spills out into the aisles. Karl Eigsti makes imaginative use of grillework, projections, platforms, and mobile furniture and fixtures to keep pace with this comedy of cinematic motion. Laura Crow designed the costumes. Dennis Parichy lighted the show, and Jonathan Holtzman composed some incidental music that includes the appropriately country-and-western ''Jedediah Kohler.''

Jed and Jedediah are playing in repertory with Shakespeare's ''Richard II,'' whose troubles have not been unveiled for the press at this writing.