A House subcommittee chairman charged yesterday that the State Department withheld from investigative agencies reports implicating more than 500 U.S. Marine security guards in possible black marketing or fraternization with Soviet nationals around the globe.

But State Department and Marine Corps officials discounted this latest accusation in the "Marine guard spy scandal" that erupted last year.

Rep. Dan Mica (D-Fla.), chairman of the Foreign Affairs subcommittee on international operations, called a news conference to reveal what he described as this "most startling" finding of a preliminary verbal report on an incomplete investigation presented to him Wednesday by the General Accounting Office, the investigating arm of Congress.

The GAO study of U.S. Embassy security and the Marine guards was requested by Mica and the subcommittee's ranking minority member, Rep. Olympia J. Snowe (R-Maine). Snowe refused to participate in yesterday's news conference, saying it was premature and against the advice of GAO investigators.

Mica left town later in the day for Florida, where he is to announce his candidacy for the Senate Tuesday.

On the basis of the verbal report, Mica said, he has drawn the conclusion that "there may have been a KGB worldwide effort to target Marines around the world" for recruitment into Soviet spy operations. He said the 500 cases are now being investigated by the Naval Investigative Service after finally receiving the information about the possible Marine Corps misdeeds from the State Department.

A State Department official said Mica appeared to be referring to a list, compiled last year by State's Bureau of Diplomatic Security, of 578 Marine security guards who had been sent home from abroad prematurely for any reason between 1980 and 1987.

The Marine Corps, which was presented with this list last summer, found the document inaccurate and expressed concern that it might be mistakenly interpreted as suggesting widespread security breaches, according to a letter to State from Maj. Gen. Carl Mundy, then-Marine Corps director of operations.

Mundy said Marine records for 1980 to 1984 have been destroyed, and that many of the 195 Marines sent home between 1985 and 1987 were not being disciplined. No charges of misconduct were lodged in 47 of the cases, which included routine transfers for health reasons. At least 41 of the other reasons for transfer were "minor," including such things as disobeying a verbal order against jogging in Beirut, according to Mundy.

A Marine Corps official said many of the 578 cases were "extremely minor" and "could not have conceivably have any tie to spying or vulnerability."

Mica also said the preliminary GAO study disclosed "no major finding of mishandling" of the case of Sgt. Clayton Lonetree by the Naval Investigative Service, but drew no conclusions about other Marine cases.