A U.S. District judge here has dismissed claims by White House Press Secretary James Brady and retired D. C. police officer Thomas K. Delahanty against the firm that manufactured the .22-caliber pistol that John W. Hinckley used to shoot the men plus President Reagan and Secret Service Officer Timothy McCarthy, Brady's attorney said yesterday.

Frederic W. Schwartz Jr. said that he was notified by a law clerk to U. S. District Judge John Garrett Penn that the portion of the suit against the gun manufacturer, Roehm of Germany, had been dismissed but that he was not told the basis for the dismissal. No written opinion had been filed as of late yesterday.

Brady and Delahanty had sought $20 million in damages from the gun manufacturer. Schwartz said Penn's decision does not affect the portion of the suit in which damages are sought from Hinckley.

Schwartz said Brady and Delahanty had sued Roehm contending that the guns that the company manufactures have been used for criminal purposes and that the firm had been notified of that fact by the U. S. Bureau of Alcohol, Tobacco and Firearms.

Roehm manufacturers the parts of the gun in Germany, and they are shipped to this country and assembled by a wholly-owned subsidiary, R. G. Industries of Miami. A suit is pending against R. G. Industries in Florida, Schwartz said.