Twenty members of the Ku Klux Klan in Alabama were indicted yesterday in Birmingham on federal charges for harassing and shooting at blacks and whites.

Among thsoe arrested were Wayne Vincent, of Sylacauga, Ala., the "exalted cyclops" of Chapter 1015, United Klans of American Inc. and William M. Rayfield, a Childersburg, Ala., police officer.

A Justice Department spokesman said the case, the result of a four-month FBI investigation, was the largest involving the KKK since the days of the 1960s civil rights marches in the South.

The indictment charges that the Klan members conspired to violate the civil rights of two local NAACP leaders, and two racially mixed couples by firing into their homes last fall.Several Klan members also were charged with impersonating an FBI agent to arrest a local white man in January.

One source familiar with the case said yesterday that the FBI was able to break the shootings cases after one of the victims, Leon R. Jarrett, complained that he had been arrested and beaten by a man who said he was a FBI agent.

The Klansmen "were acting as sort of a vigilante group against blacks and whites," the source said.

The indictment charges that Klan leader Vinvent gave one his members a 12-guage sawed-off shotgun last November. The gun was used to fire into the homes of the NAACP leaders and the two couples.

The civil rights activists, Willie, J. Williams, of Sylacauga, and Charles Woods, of Childersburg, had been working to get jobs for blacks in the local police and fire departments, a Justice Spokesman said. Woods had complained about alleged polce brutality and harassment of blacks he added.