Washington - Watergate Special Prosecutor Archibald Cox expressed "extreme interest" in a 1970s criminal investigation of New York Yankees owner George Steinbrenner for illegal campaign contributions, according to documents released Thursday.

Then-FBI Director Clarence M. Kelley relayed Cox's concern in a memo on Aug. 16, 1973, to the bureau's Cleveland office, saying agents needed to make sure the probe received "the same, immediate and preferred handling" as other criminal cases then growing from the Watergate scandal.

The memos were included in a 400-page release of Steinbrenner's FBI file Thursday. Most of the material focused on the Watergate-era federal probe that led to the shipbuilding magnate's 1974 conviction for illegal contributions to disgraced President Richard M. Nixon.

There are scant references to Steinbrenner's later pardon by President Ronald Reagan and nothing on his turbulent career as the Yankees' "Boss." The Associated Press and other news organizations requested the file under the Freedom of Information Act following Steinbrenner's death in July.

"The office of the Special Prosecutor has indicated extreme interest in this matter and requests that the interviews be conducted as soon as possible, and as nearly at the same time as possible," Kelley wrote in the memo on the investigation into Steinbrenner and his Cleveland-based American Ship Building Co.

Another FBI memo, dated Oct. 17, 1973, says the "investigation is to be afforded highest priority and security. Cleveland (office) to assign most capable personnel to achieve prompt positive results."

Among other things, the FBI was investigating whether employees were told they would be reimbursed by the company for campaign contributions, a violation of campaign finance laws.

Steinbrenner was indicted the following year and vowed to prove his innocence in court. But in August 1974, just two weeks after Nixon resigned, the Yankees owner pleaded guilty to two charges in the case and was fined $15,000.

American Ship Building Co. executives told FBI officials in signed statements that they received bonuses around the same time they made donations to Nixon's campaign. The payments varied from $2,800 to $3,500, according to a report on Aug. 30, 1973, by the Cleveland office of the FBI.

The employees claimed the donations "were all of their own desires and in no way were motivated or solicited by George M. Steinbrenner or any other company officials," the report said.