A staff aide to Rep. Wyche Fowler (D-Ga.) was robbed at gunpoint by two youths last night as he was walking in the 500 block of South Capitol Street. Two suspects were arrested and charged in the holdup minutes after the 8:15 p.m. incident.

D.C. police detectives said R. William Johnstone Jr., a legislative assistant to congressman Fowler, was approached on the street by a youth who said: "I have a gun. Give me all your money."

Johnstone told police he began reaching for his wallet when a second robber approached him from behind, put a gun into his back and grabbed the wallet. Both robbers then fled.

Johnstone immediately notified a nearby Capitol policeman, who radioed a lookout for the two holdup men. Moments later, a second Capitol polceman spotted two youths who fitted the robbers' descriptions running about two blocks from the scene of the holdup.

The second officer stoped the youths, and Johnstone later identified them as the pair who had robbed him. His wallet and a small caliber pistol were taken from the suspects, police said.

Charged with armed robbery in the incident were Anthony Dunn, 19 of 935 Waller PL. SE, and a 16-year-old Northwest youth.