A holdup victim yesterday sued two firms that made a "Saturday night special" he was shot with, contending that they should have known that "it was extremely likely and foreseeable that their products would be used for illegal and dangerous activities."

Olen J. Kelley of Jessup filed a $500 million lawsuit in Montgomery County Circuit Court, naming as defendants Rohm Gesellschaft, a West German firm that made the parts, and R. G. Industries, Inc. of Miami, which assembled the .38-caliber revolver that Kelley said was used to shoot him in the chest at his grocery store in Silver Spring last March 21.

The weapon was confiscated from the person convicted of the robbery, according to Howard L. Siegel, Kelley's lawyer. Siegel said last night that while similar suits have been filed in this country, he has never known of one to go to trial.

The nine-page petition alleges that the defendants "recklessly and wantonly designed, manufactured, promoted, marketed and distributed their products into interstate commerce for the sole purpose of making a profit when they knew that the said product was likely to injure innocent persons . . . "

The suit contends that the handgun was "defectively designed" and that a "safer alternative" design could have been used to lessen the "adverse consequences" of the product.

No representatives of the gun companies could be reached for comment.