A McDonnell Douglas Corp. executive was indicted on perjury charges by a federal grand jury in Washington yesterday in connection with an alleged scheme to bribe Pakistan officials over the sale of DC10 jetliners.

Sherman Pruitt Jr., who was sales manager for Douglas Aircraft Co. at the time of the alleged scheme in the mid-1970s, already is facing fraud and conspiracy charges with three other top McDonnell executives filed as part of the same investigation last November.

It was not immediately clear yesterday why the perjury charges weren't contained in the original indictment, though one source said the evidence to back up the perjury charge wasn't obtained until recently.

John M. Bray, Pruitt's attorney, had no comment yesterday on the new indictment.

The charges last fall were the first brought against corporate executives in a long-running Justice Department-Customs Service investigation of alleged corporate bribery overseas.

Pruitt and the other three men were accused of concealing from U.S. government agencies and the government of Pakistan $1.6 million in secret commission payments that were added onto the cost of four DC10s.

The perjury charges allege that Pruitt lied when he told a grand jury in December 1977 that he didn't have a foreign bank account and when he sowre he didn't know who Douglas Aircraft's agent in Pakistan was making payments to.