Gordon Butler, private investigator, was taking a Saturdasy afternoon nap Aug. 12 in his Silver Spring home when the phone woke him up.

He had been hired three days earlier to find a missing boy, and he had instructed the boy's mother not to do anything during the weekend without talking to him first. It did not take him long after the telephone rang to figure out that the mother, I. Grace Viscidi, had ignored his adviced.

"All hell had broken loose," said one of Butler's men over the phone. Sixteen minutes and 25 miles later, Butler was at the Viscidis home in suburban Vienna, asking "why and how" family friends had found 12-year-old Billy's body buried in his backyard.

The discovery of the shallow backyard grave transformed a routine search for a runaway - a case that Butler at first refused to take - into a celebrated investigation that has made Billy Viscidi a household name in the Washington area.

As insiders in the mysterious death, which has yet to be ruled accident or murder, Butler and his partner, M. Morgan Cherry, have lost what they claim they need to make a living - anonymity.

The detectives, who work out of a secluded basement office in Annandale, have been seen on television. (See INVESTIGATORS, C2, Col.1) ( INVESTIGATORS, From C1) Their names and photographs have been in newspapers for more than a week.

Butler, 35, who got interested in detective work after reading Mickey Spillane mysteries while working for his PhD. in sociology, said he now finds himself closer to cloak-and-dagger drama than he wants to be.The detective, who is a strict Seventh Day Adventist and who had not worked on the Saturday Sabbath for three years before he got that phone call, specializes in divorce and child custody cases.

Since Billy's body was found inside a yellow plastic bag, the detectives have taken to working all night, catching sleep when can on their office sofas which they say have been picked ragged by the nervous fingers of their clients.

Butler and Cherry, considered two of the most competent private detectives in the Washington area by lawyers who deal with them, say they have a "gut feeling" about how Billy died. Police say only that the boy died on July 25 after being assaulted in the living room of his house.

The private detectives also say they cannot be sure about the death until blood tests are completed this week, and they refuse to divulge what they know about the case.

Commonwealth's Attorney Robert F. Horan Jr., the Fairfax prosecutor in charge of finding out how Billy died,said the two private detectives "have walked that very narrow line that they have to walk between being investigators and being accessories after the fact to what may be a crime."A person would be an accessory after the fact, Horan said, if he helped a felon "elude punishment."

The private detectives, whose typical surveillance work is done in disguises using theatrical makeup and phony beards, claim the key to the Viscidi case lies in what they found out on the day before the body was found.

The prosecutor's office is "very interested" in what Butler and Cherry know and when they found it out, a spokeman said.

Butler said last week that what he and his partner know amounts to "suspicions." And, "We don't have to tell anybody our suspicions," Butler said.

Butler, who has taught criminology at the Prince George's County Police Academy, became a detective while working on his sociology doctorate at Louisiana State University. He did detective work to make extra money and claims he has been so successful that he has never found time to write his doctoral dissertation.

A stocky and garrulous man with four children, a wife and a $600 a month mortage, Butler is not above using sociological jargon for a private eye's trick.

Representing an insurance company that did not want to pay off a woman who claimed a total disability, Butler discovered that the woman regularly went bowling. He asked the owner of the alley if he could bring in his partner, floodlights and cameras for a sociological study of the sport.

A photograph if the "disabled" bowler in action is taped up in the detectives' darkroom, a reminder of how they foiled her insurance claim.

Butler's partner, who took that photograph and who points at it with pride, is a former Marine who could not find work as a cop because his fight ear-drum was destroyed on a simulated minefield during advanced Marine training.

M. Morgan Cherry, 30, who claims he once tailed a man by car all the way from Fairfax to San Jose, Calif., without being spotted, grouses that the Viscidi case is disrupting his business, which operates under the name Legal Investigations Inc.

"I'm going to have to buy a new car because mine was on television so many times," Cherry said. "Day-to-day business has suffered because we've had to stick with this Viscidi case."

Cherry, a 6-foot-3 former Texan who wears sharp-toed cowboy boots and carries a .45 automatic pistol in his belt, says that normally people never remember his appearance.

"I change my hat. Sometimes I'll put a scar (using make-up) on my face that 'll seem to run right through my eye. People look at the scar, they don't look at me," Cherry said.

The detective, a licensed weapons instructor in Virginia, habitually carries his .45 loaded with a low-velocity bullet that expands on impact.

"They're (the bullets) are the safest. They do the job of stopping people and they don't ricochet," Cherry said. Neither he nor his partner will say if they have had to use their pistols as private detectives.

Cherry and Gordon, who employ four other detectives full time, charge clients $22.50 an hour for each detective on the job, plus expenses, plus 28 cents a mile for auto travel.

"The average murderer and rapist cannot afford us," Butler said. Their clients are primarily insurance companies and attorneys representing weathly clients in divorce or child custody, he said.

In three years in their hard-to-find office off Little River Turnpike, not one teary-eyed, voluptuous or scorned wife has wandered into their office and, in the pulp-novel tradition, poured out her heart to the detectives, Cherry said. "We don't want anybody walking in here. That's why we picked this office."

One of the signs of their office door is intended to divert the unannounced. It reads, "American Sportsman Association Inc."

Butler said his policy is never to represent anyone unless they have an attorney. "That policy lends itself to our getting paid, he said.

Neither Butler nor Cherry offers little praise for most of their colleagues in private eye business. "Most of them are sleazy," Butler said. "We would'nt take them to a dog fight if they promised to win."

In the Viscidi case, which Butler and Cherry decided to accept after talking to Billy's mother at her home, the initial contact was made through the family's lawyers

Last week that contact had grown to the point that, according to Butler: "We've taken over the care and feedingof the family."