Former congressman Allard Lowenstein last night accused California police authorities of concealing evidence about the assassination of Robert F. Kennedy and called for a reopening of the case against alleged assassin Sirhan Sirhan.

"We've been asking for access to the ten volumes of evidence for a year and a half, but the police have refused us." Lowenstein told the Law School Forum audience. "Instead of that, what the police have done is to lie to the public with increasing vigor."

"The bullets fired from Sirhan's gun do not match the bullet removed from the head of Senator Kennedy," he said. "It is time to take the facts of the assassination to the people of this country."

Robert Joling, president of the American Academy of Ferensic Scientists, said last night that powder marks on Kennedy's neck prove that the gun which killed Kennedy was held between one and three inches from the senator's neck. He said that witnesses say Sirhan never came within a yard of Kennedy.

"From the evidence in my possession I can not believe that any bullet fired from the gun of Sirhan could have killed Senator Kennedy," Joling said.

The California Supreme Court ruled against reopening the Sirhan case last January on the grounds that no new evidence had been found since the time of Sirhan's trial in 1968. Defense attorneys for Sirhan did not present ballistics evidence at that trial, arguing that Sirhan had killed Kennedy but that he was mentally unstable and should not receive the death penalty.

Neither Lowenstein nor Joling would comment specifically on whom they thought had killed Kennedy or why police refused to cooperate with their investigations.