In an unusual exchange yesterday, independent counsel Lawrence E. Walsh and the Justice Department bitterly blamed each other for the dismissal of the Iran-contra criminal case against former CIA operative Joseph F. Fernandez.

The Fernandez indictment, which was originally brought in April 1989, was dropped earlier this month after Attorney General Dick Thornburgh, following several court actions, refused to permit release of classified CIA information that the courts had ruled was needed for Fernandez's defense.

In a report sent yesterday to the chairmen and ranking minority members of the House and Senate intelligence committees, Walsh asked for a congressional inquiry into Thornburgh's actions saying they "underscore the need for objective standards to govern the release of classified information in criminal prosecutions."

Walsh said "this is particularly true when there is an appearance of conflict of interest because the agency refusing disclosure {meaning the CIA} is itself a subject of investigation." Fernandez planned to use the CIA's own information to show that CIA's top officials were aware and participated in aiding the Nicaraguan rebels at a time when Congress had prohibited U.S. military assistance to the contras.

Walsh said that in his final report he would discuss in detail what he described as "the power of intelligence agencies to frustrate investigations of their own misconduct by professing exaggerated concerns for the preservation of national security."

In a quick response to Walsh's charges, Assistant Attorney General W. Lee Rawls yesterday sent a letter to the same members of Congress.

In it he said that Justice Department sources assessed Walsh's prosecution of Fernandez "as a relatively weak one which would not have been brought had Fernandez been willing to cooperate with the investigation." Rawls said Thornburgh in his decision to withhold the secret information had taken into consideration "the relative significance" of the case for Walsh's overall prosecution.

Rawls went on to suggest that while a conviction of Fernandez might have made him a cooperative witness against other individuals, "other mechanisms are available . . . to elicit that cooperation."

Although Rawls did not mention it, one means would have been for Walsh to give Fernandez a grant of immunity from prosecution for his testimony as Walsh had done with other witnesses.

Yesterday, sources outside the government said Walsh may now be planning to do just that with Fernandez, putting him before a federal grand jury within the next month.

Walsh and Rawls also accused each other of errors in the legal tactics the Iran-contra prosecutor and the Justice Department followed that led to U.S. District Judge Claude M. Hilton dismissing the case.

Walsh asserted that Thornburgh and the CIA dragged out their decision on whether CIA classified information would be released to Fernandez's lawyers in a way that irritated the courts. "The Court of Appeals and the District Court," Walsh wrote, "both justified the severity of the sanctions imposed in this case in part upon the delays forced on the independent counsel by the intelligence agencies and the attorney general."

Rawls wrote that Walsh's "tactical decision" to have Hilton evaluate "categories" of secret information rather than "each item of classified information" was one key in forcing Thornburgh's action "because admission of all of the classified information would seriously damage the national security."