Genevieve Christensen has said she refuses to believe her son, William Dean Christensen, could kill. That faith, the kind that prosecutors portrayed as a love that went lawless, led to her conviction yesterday on charges of harboring a fugitive and conspiring with her frail 79-year-old husband to protect their son, a convicted murderer and a suspected serial killer.

"I feel as though I'm not guilty, is all," the 77-year-old grandmother from Bethesda said with little emotion to District Court Judge Edwin Collier before he sentenced her to a year in jail on each count, suspended all but 60 days, and fined her $2,000.

Genevieve Christensen and her husband, David, are the parents of William D. Christensen, 40, who has been convicted of one murder in Philadelphia, indicted for another in Scranton, Pa., is suspected of two more in Canada, and has been convicted on various rape offenses in Montgomery County and Montreal. He also is being investigated in connection with 12 slayings of young women along the East Coast and in Canada from 1980 to 1983. Currently, he is serving a prison term for murder.

The prosecution charged yesterday that Christensen's mother and father, who had a heart attack during his last court appearance and was described as too ill to be present yesterday, allowed some of those slayings to occur in 1982 and 1983 by hiding their son in a house they bought in Philadelphia, paying his bills and never telling authorities.

"In May 1982 . . . she was told with her husband in no uncertain terms that her son was wanted," Assistant State's Attorney Robert Dean said. "They promised not to help him . . . and then in September 1983, she bought him a house. It was a blatant disregard of her obligation."

Defense attorney Victor Crawford did not contest the prosecution's claim.

He instead questioned whether the case could be brought to trial in Maryland when the alleged activities occurred in Philadelphia.

Judge Collier rejected that claim and added, "There's strong probability that one or more persons would still be alive today" if she had turned in her son earlier.

Crawford said after yesterday's proceeding he would ask the state's highest court to overturn the verdict on jurisidictional grounds. "I believe the state has shown beyond a reason of a doubt that they bought the home for their son," he said, "but in the state of Maryland, they've done nothing wrong."

The son was last arrested Dec. 4, 1983, minutes after the fatal shooting of a 51-year-old Philadelphia man outside a bar. He had a record of rape convictions that began in 1973 and at one time served nearly eight years in jail for a rape in Montgomery and then another one-year sentence for a similar charge in Canada. He was still wanted on another rape charge in Montgomery at the time of the slaying arrest and since has been linked by authorities as a suspect in string of murders that occurred in states along the East Coast in 1982.

Since the younger Christensen's conviction in 1984, the elderly couple has not had contact with him, Crawford said yesterday. David Christensen, a retired Army intelligence officer who had a heart attack during a court proceeding in March, has had three more heart attacks and is bedridden at home. His wife of 54 years spends her days tending to his health, Crawford said.

"They feel he's innocent," Crawford said about the parent's loyalty to their son. "Nothing you can say or do will convince them otherwise."