A robber, who had been arrested recently in a murder-for-hire scheme, was shot and killed on a busy Northwest Washington street yesterday by a Washington Post newspaper distributor in an exchange of gunfire that also left a 7-year-old bystander wounded in the legs, D.C. police reported. An accomplice of the slain holdup man got away with $300 in cash from the Post distributor.

Police said Ronald Dell Shepherd, 32, of 1387 Quincy St. NW, was shot, at least twice by Samuel Williams, 45, an independent Post distributor and recently retired D.C. police officer, after Williams was accosted in his delivery van parked in front of the Town & Country Market, 823 Upshur St., near Georgia Avenue in the Petworth area.

Williams was not harmed in the incident. Police identified Shepherd as one of six suspects charged early this month with first-degree murder in a murder-for-hire plot. Shepherd had been released in third-party custody after being arrested in the execution-style shooting March 11 of George Cole, 62, a custodian of a Silver Spring church. Cole's wife, Besty, was charged with hiring Shepherd and four other persons for $3,000 to kill Cole to collect insurance on his life.

In yesterday's incident, several shots were exchanged between Williams and his two assailants on the sidewalk in front of the Town & Country Market. Kevin Simmons, a 7-year-old neighborhood child, was caught in the cross fire and wounded in both legs. He was listed in fair condition last night at Children's Hospital.

Police said the holdup men approached Williams about 2 p.m. in his van as he was collecting payments in the neighborhood for his regular newspaper deliveries. He surrendered $300 he had in his pocket, police said, but when the robbers spotted a vault-like safe-deposit box in the van, they demanded it contents.

Police said the assailants than noticed Williams was carrying a pistol. A struggle ensued, they said, and the three men spilled out into the sidewalk where the shots were exchanged, sending bystanders scurrying for cover.

One of the holdup men escaped with $300. Shepherd started to run away, then stumbled into a nearby alley and fell, fatally wounded by Williams' gunfire, police said.

Williams, who lives in Avondale, Md., had started his job as an independent distributor for The Post less than a month ago. Jake Terrell, his supervisor, said Williams' predecessor in the Petworth distribution area also had been robbed of about $1,500 three months ago in the 700 block of Kennedy Street NW.

Though the distributors' vans are unmarked, neighborhood thieves seem to know that the drivers often carry large amounts of cash, Terrell said.

Williams, who did not have a permit to carry a pistol as required under the District of Columbia's strict gun-control law, was charged with carrying a dangerous weapon.

A 20-year veteran of the D.C. police force who retired last August as a sergeant, he was well known among fellow officers in the 3rd District, where he worked, and among the homicide detectives who charged him yesterday.

"One of the hardest things I ever had to do was charge my good friend Sgt. Williams," homicide Lt. Carl J. Alexander said last night.