James F. Reagan, Cambridge Chief of Police, declared a virtual black-out yesterday on all future news concerning the murder of Jane S. Britton, the 22-year-old Harvard graduate student who was found murdered last Tuesday.

Reagan told reporters at a special news conference on the killing that the police will not release any further discoveries until he personally gives his permission.

The reason for the black-out, Reagan said, was that there have been "inaccuracies" in press coverage of the killing. Reagan did not say what these inaccuracies were.

Police began speculating that the killer performed an ancient burial rite over Miss Britton's body after they found iodine oxide, a reddish-brown powder, on the walls, ceiling, and floor of the apartment and on her body.

Primitive tribes in Iran and France sprinkled a similar powder, red ochre, over the bodies of their dead in order to purify the bodies and to drive off evil spirits.

Caught as he was leaving his office for the day, Reagan said that police have now found the sharp-edged stone which had been missing from Miss Britton's apartment. He refused to say where the stone was found.

The stone, a gift to Miss Britton from Mr. & Mrs. Donald D. Mitchell, two friends, was an archaeological souvenir. Police say Miss Britton was killed by five blows to the head from a sharp object and left lying face-down on a mattress in her apartment.

Police questioned four people involved in the case yesterday, including James H. Humphries and Mr. and Mrs. Mitchell, all graduate students in anthropology. Humphries and the Mitchells discovered Miss Britton's body.