A top lieutenant in an Alexandria-based massage parlor operation unexpectedly pleaded guilty to recketeering yesterday and immediately was whisked before a federal grand jury where he reportedly began disclosing details of the operation.

Federal prosecutors described the guilty plea by Clyde Ballard (Skip) Stovall Jr., an assistant to massage parlor owner Louis Michael Parrish, as a major step forward in their 16-month investigation of Parrish's net-work of parlors and out-call service.

The FBI has called Parrish's $1 million-a-year business "the largest and most sophisticated commercialized prostitution business" in the Washington area.

The sandy-haired 32-year-old Stovall spent three hours before the grand jury that is probing Northern Virginia's massage parlor and bingo operations.

Stovall brushed aside reporters' questions as he left the federal court-house, saying only that he was feeling "terrific."

Stovall's guilty plea was the first conviction federal officials have obtained since their investigation began in 1977. One reason they were pleased at Stovall's plea was the Parrish had made his employes take lie-detector tests to determine if they were undercover police agents, or disloyal to Parrish, a practice that apparently made it difficult for investigators to get witnesses from inside the organization.

Federal officials are investigating allegations of interstate racketeering, prostitution, gambling and possible corruption of local officials.

"This is a major step in the investigation," one kowledgeable federal official said later. Stovall was described by the official as the No. 4 person in Parrish's network.

Officials said Stovall was in direct control of four of Parrish's 11 parlors and out-call services. The parlors, known as Bunny's, Phase II. Hearts and Tiki Tiki, were among the most profitable in the chain, officials said.

Stovall, who faces a sentence of up to five years in prison and a $10,000 fine on the racketeering charge, was released on a $1,000 personal recognizance bond, pending Oct. 13.

U.S. Attorney William B. Cummings presented the case against Stovall before U.S. District Court Judge Albert V. Bryan Jr. in the unscheduled proceeding early yesterday morning.

Cummings told the the judge that on May 22 Stovall took an undisclosed amount of money from the Foxy Lady Outcall Massage Service, 1001 Connecticut Ave., NW in Washington, and deposited it in a night depository at the United Virgimia Bank branch in Alexandria.

The "proceeds were from illegal prostitituion . . . and pandering" activities run by Parrish, Cummings said.

Stovall agreed to testify before the federal grand jury, and at any subsequent trials, Cummings said.

Stovall stood quietly at the docket in Bryan's nearly empty courtroom yesterday, wearing a European-cut three-piece blue suit. He was accompanied by his attorneys, Lawrence Schwartz and William Jordan Temple.

Each time Bryan asked him questions designed to show that the understood the significance of his guilty plea and the possible penalties he faced, Stovall answered in a firm voice that he did.

Prosectors would not discuss what Stovall told the jury, which yesterday concluded its current session. Earlier prosecutors had said the jury probably would not bring any indictments until next month.

Another witness, who appeared before the jury yesterday, said he was asked about his ownership of an Alexandria massage parlor and about efforts a year ago by Alexandria lawyer james I. Burkhardt, who has represented Parrish in the past, made to purchase his parlor for an unnamed client. The witness said he refused the offer.

Burkhardt yesterday confirmed the attempted business transaction, but would not name the client involved.

The massage parlor owner said he was also asked to describe the Arlington masseuse training school federal sources have said was run by Parrish's mother, Effie Haggerty. The massage parlor owner said he told the (See PARLORS, C9, Col. 6) (PARLORS, From C1) jury that the women received virtually no training. In fact, the owner said he testified, "the main instructor was a blind man."

The jury broke into laughter, according to the witness.

The grand jury also heard from Dawn L. Peck yesterday, named by an informant in an FBI affidavit as the manager of the Foxy Lady Outcall Massage Service. Officials have previously said the out-call business, which utilized interconnected telephone lines to receive requests and direct women to hotel rooms and offices for sexual services, was among the most profitable of Parrish's operations.

One woman scheduled to appear yesterday took an overdose of drugs and wwas hospitaliezed, an official said.