Attorneys for presidential press secretary James S. Brady, who was critically wounded more than a year ago in John W. Hinckley Jr.'s attack on President Reagan, are seeking $100 million in damages from the companies that manufactured and assembled the handgun that Hinckley used in the shootings.

The complaint against the makers of the .22-caliber pistol--described by police as a classic Saturday night special--was added this week in behalf of Brady and his wife, Sarah, to a lawsuit filed earlier that seeks $46 million in damages from Hinckley for assault and negligence.

In papers filed in U.S. District Court here Monday, Brady's lawyer, Jacob A. Stein, alleged that the manufacturer of the weapon, Roehm GmbH of Sontheim, West Germany, and the distributor, RG Industries Inc., based in Miami, produced the gun knowing that it was "the weapon of choice of numerous persons of bad character" and posed a risk to the public. Officials of the Miami firm, which is owned by Roehm, could not be reached for comment late yesterday.

The complaint also contends that the companies knew, or had to know, that the gun, which the suit describes as "poorly constructed and unreliable," was sold without an adequate effort by distributors and retailers to prevent purchases by persons who intended to use the weapon for "improper purposes."

According to court papers, the two companies were responsible for 1.1 million handguns of the same type entering the marketplace from 1971 to 1979.

Hinckley, who was found not guilty by reason of insanity in the shootings of Reagan, Brady and two others, bought the gun in October 1980 at a Dallas pawn shop for $39.95.