For most of his adult life, Rep. Stewart B. McKinney (R.-Conn.) says he has been carrying around two wallets: the one in his right hip pocket is for him and the one in the left pocket is for muggers.

But early Friday morning, both wallets here empty when McKinney left his $127,000 Capitol Hill home, drove two blocks to buy a pack of cigarettes at Mr. Henry's bar at Pennsylvania Avenue and 6th Street SE and re turned to his car where, he said, two young thievee confronted him and demanded money.

So, the blunt-talking ranking Republican on the House District of Columbia Commitee said, "I just went bananas. I started screaming at them."

Before it was over, McKinney said one of the youths produced a small caliber pistol, waved it menacingly in the congressman's direction and fired it from about five feet away before both young men fled.

"My theory is that it was a starter gun," he said, "I obviously heard the bang, but I didn't hear the air break of the projectile."

A crime prevention official who asked not to be identified said it is usually a mistake to react to potential attackers the way McKinney did. Asked if he has considered that his fiery outburst could have brough him injury, McKinney replied: "No. It was strage, it was unreal, it was adrenalin.

"I think they [the youths] expected to find a drunk, Capitol Hill staffer and instead they found a sober . . . first class, Grade A nut . . . I went bizzare, animal."

McKinney said that Thursday evening he attended a constituent reception at the Rayburn Office Building, watched President Carter's energy address at home on television, participated in a radio talk show by telephone and was reading and watching "Starsky and Hutch" before he was struck by an urge for a cigarette.

"It just shows you that cigarettes can really be dangerous," he said.

McKinney said he does not want an FBI investigation into the incident. "It was not an attempted assassination of a federal official. It was an attempted mugging of a person who lives in Washington."

During 1978 Rep. Robert H. Michel (R-III.) was robbed and beaten outside his Capitol Hill residence and Sen. Robert Morgan (D-N.C.) was robbed three blocks east of the White House.

D.C. police are following up on one lead McKinney provided: the description of a car that sped away from the interseciton of Pennysylvania Avenue and 6th Street SE just after the attempted robbery. CAPTION: Picture, STEWART B. MCKINNEY . . . "I went bizarre, animal"