A federal grand jury today indicted two more former Houston policemen on civil rights violation charges in the fatal police shooting of an 18-year-old youth in 1975.

Three years after local prosecutors rubber-stamped a police department investigation, Walter F. Plaster and John S. White, both relieved of duty last April, were indicted on one count each of conspiracy to deprive Billy Keith Joyvies, 18, of his civil rights while the two were policemen.

The indictments were announced by U.S. Attorney J. A. (Tony) Canales, who has brought a series of charges involving civil rights violations against police officers.

Suspected of stealing a tool box from a pickup truck, Joyvies was killed by police after they riddled his car with gunfire at the end of a long and wild chase. They said they killed the youth when they saw his arm move, and a 25 cal. pistol was found on the floor of the youth's car. The gun, however, was later traced to a Houston policeman.

It was the second case this year in which ex-officers have been indicted in connection with the killing of a so-called "armed" suspect but in which federal grand juries traced the weapons instead to policemen.

Plaster and White face maximum sentences of 10 years and $10,000 fine if convicted.