A 23-year-old escaped convict who reportedly once said his life's ambition was to kill a policeman has been charged in warrants with two robberies Thursday night in upper Northwest Washington, D.C. police said.

The suspect was identified as Ronald Jennings, who police said escaped Sept. 18, 1976, from federal custody in Petersburg, Va. They said he had been sentenced on first-degree murder, armed robbery and weapons charges.

Police, who gave Jennings' last known address as 2732 Bruce Pl. SE, said they have charged him in connection with the robberies Thursday night of a cab driver and a Safeway store at 4840 42d St. NW.

Earlier this month, police issued a flyer listing Jennings as wanted in another armed robbery here. In that incident May 2, police said, four men robbed about 50 persons at 1008 11th St. NW, a building authorities suspect was frequented by prostitutes and their customers.

The flyer said Jennings has been arrested in the past on "numerous" counts of armed robbery and that "on several occasions . . . has attempted to shoot police officers when the officers attempted to arrest him."

After the Safeway store robbery Thursday night, police said, as the holdup man was leaving he told an employe who had declined to comply with his demands: "Lady, you are crazy . . . real crazy . . ."

According to police, Raphael Akintewe, 35, a driver of a Liberty Cab, picked up a passenger in the 4200 block of Wisconsin Avenue Thursday night and was ordered at gunpoint to drive to the 4800 block of Wisconsin Avenue, near the food store.

On arrival, police said, the gunman took the driver's wallet containing $12, seized the ignition keys and locked the driver in the cab's trunk. When the gunman left the cab, the driver escaped by using a tire iron and went to find help.

As he was telling his story to a policeman, the police radio reported a holdup at the Safeway store, authorities said.

Inside the store, police said the robber went to the locked cashier's office. Grace Oliver, 46, was behind the window.

"How are you doing?" the robber reportedly asked.

"Fine," Oliver replied. "How are you?"

Smiling, the robber asked for the store's cash, but Oliver said it had been removed for deposit.

Persisting, the robber opened his shirt to show what appeared to be a gun. Police said Oliver still did not comply. At this point, they said, another employe came up and engaged her in conversation, and the robber went to the rear of the store, found the manager and forced him to open the office.