Ford Motor Co. officials said yesterday they will cooperate with an Elkhart County (Ind.) grand jury investigating a fatal Pinto crash but that the testimony of Chairman Henry Ford II is not necessary.

A county prosecutor heading the investigation said Wednesday he will call Ford and former Ford President Lee A. Iacocca to appear before the panel to answer questions concerning the design and safety records of the subcompact cars.

The grand jury is seeking to determine whether criminal negligence charges should be filed against the automaker as a result of a fiery Pinto crash near Elkhart in which three teen-age girls were killed.

"The company is prepared to cooperate with the prosecutor to assist the grand jury in its deliberations," H. R. Nolte, Ford vice president and general counsel, said. "We believe, however, that the needs of the grand jury can be met by the appearance of other company personnel and that it will not be necessary for Mr. Ford or Mr. Iacocca to appear."

Ford is recalling 1.5 million of the Pintos and the companion Mercury Bobcats produced from 1971-76. It plans to install two protective shields between the fuel tank and the rear axle, a longer filler pipe and a different gas cap.