At 4:10 p.m. Sunday, District of Columbia police arrested a slight, bearded 28-year-old man in a Northwest Washington hotel and charged him with stealing a radio.

Five hours later police officials ran the man's name through the nationwide police computer system, a routine check that seldom turns up anything out of the ordinary.

This time, however, they found that their subject, Michael Owen Perry, was wanted in Louisiana on warrants charging him with shooting to death his mother, father, two cousins and a 2-year-old nephew.

Perry, of Lake Arthur, La., was held in the cellblock at police headquarters here Sunday night and, at a hearing in D.C. Superior Court yesterday, waived extradition and was ordered returned to Louisiana.

Perry was arrested in the lobby of the Annex Hotel, 1440 Rhode Island Ave. NW, after a man hailed a police car and said his FM-AM radio had been stolen by a man in the hotel.

Police officers said they found the radio, arrested Perry at the scene without resistance and took him to the 3rd District police station.

D.C. police notified Louisiana authorities, and officials in Jefferson Davis Parish, where the slayings took place. Ted Gary, the parish's chief criminal investigator, identified Perry as the suspect they wanted.

At a hastily called press conference here yesterday, Gary said: "I can tell you that he brought a blanket of fear" into Lake Arthur. "When he was arrested yesterday everybody breathed easier."

Police said yesterday that Perry, a former mental patient, apparently had been in Washington for two weeks. A search of his hotel room late yesterday turned up seven small-screen TV sets, police sources said. Police here are trying to determine what Perry had been doing in Washington.

Louisiana authorities said the slayings were discovered July 19 in two Lake Arthur homes when a man, looking for his stepson, entered a neighbor's house and found two bodies, one of the stepson, Brian LeBlanc, 21, and one of LeBlanc's cousin, Randall Perry, 19. The two men, both of whom were cousins of Perry, had been shot in the head at close range with a shotgun, police said.

The man called police, who said they then noticed bloodstains on the front door of the home of Perry's parents, two doors away. Police entered the home and found the body of Perry's father, Chester, 48, in a crouched position in the living room. His mother, Grace, 47, and his nephew, Anthony Bonin, 2, were found dead on the kitchen floor. All had also been shot in the head with a shotgun, police said.

Perry, who had been in and out of Louisiana mental hospitals, immediately became the main suspect, Gary said in an interview yesterday.

Perry, an unemployed oil field roustabout, was a longtime resident of Lake Arthur. He had been shot in a bar several years ago and lived off Social Security as a result of the injuries he received in the shooting, Louisiana authorities said. In 1981, he spent two months in Washington trying to obtain more money from Social Security officials.

Police said that in the several months before the Louisiana slayings, Perry had written a number of rambling letters to singer Olivia Newton-John that at times expressed adulation and at other times appeared threatening.

During a search of Perry's trailer home in Lake Arthur, Louisiana police said they found several names written on a piece of paper, including that of Newton-John and "Judge O'Connor," which police believe refers to Supreme Court Justice Sandra Day O'Connor. Police declined yesterday to speculate on what the names mean.

At his court hearing yesterday, Hearing Commissioner John W. King asked Perry if he was fully aware that by waiving extradition he would have to be returned immediately to Louisiana, where he is facing five charges of first-degree murder.

"The thing is they might need me in Louisiana," Perry answered. "I think it's best for me to go back there and find out what this is all about."