CROWN POINT, Ind. (AP) _ A prosecutor ruled today that a man who died from 32 hammer blows to the head was murdered, and Hobard police agreed to reopen the case that they originally had ruled a suicide.

However, Lake County Prosecutor Jack F. Crawford said ''there is insufficient evidence to charge any person with the murder.''

Crawford said he made his decision after reviewing an investigation conducted by the Indiana State Police into the April 6, 1985, death of James A. Cooley, 52, of Hobart.

Hobart police had maintained that Cooley battered himself to death with a claw hammer in the basement of his home.

Police Chief Larry Juzwicki said today that because of Crawford's opinion, the Cooley investigation would be reopened and reclassified from suicide to homicide. But he said he would have no other comment.

''This decision is based primarily on the medical evidence offered by several pathologists,'' said Crawford. ''That evidence established that the amount, location and severity of the hammer blows to Mr. Cooley's head are inconsistent with a finding of suicide.

''Although there was evidence which could have led investigators to conclude that the death was suicide, that evidence is outweighed by the medical findings in this case.''

Crawford said the same conclusion was reached after a thorough investigation by state police detectives.

Lake County Coroner Daniel D. Thomas has contended that Cooley could not have remained conscious long enough to hit himself 32 times, but police cited evidence gathered by a blood splatter expert from Oregon, Rod Englert, who examined the findings in the case.

Englert said the pattern of blood in the room showed that no one could have stood over Cooley to deliver the blows. He also said that because Cooley's body was found propped against a door, an assailant would not have been able to kill him and leave the room.

Thomas said Tuesday he had been confident the state police investigation would support his conclusion because he and state police used the same forensic pathologist, John E. Pless.

But the lengthy dispute could make it difficult to find the person who killed Cooley, Thomas said. ''It's been almost a year and the paths to finding a murderer are pretty cool.''