The Prince George's jury that took 25 hours to convict 29-year-old Howard Hines for the vicious murder of a young Japanese woman deliberated less than four hours yesterday before sentencing him to life in prison instead of death.

Based on that decision, Circuit Court Judge Audrey Melbourne imposed two consecutive life sentences for the 1979 murder and attempted rape of 22-year-old Michiyo Nakada, plus 10 years for a third degree sex offense--all of which are to run after the remaining six years Hines must serve in Alabama for a probation violation. Hines had been on parole following a rape conviction at the time he attacked Nakada. Joseph M. Niland, one of Hines' attorneys, speculated that his client will not be eligible for parole now for about 50 years.

The Hines sentencing may be the first time new, tougher state sentencing laws will apply to a murder case in Maryland, although court officials say it is unclear whether those laws apply to crimes committed before July 1. David M. Simpson, Hines' prosecutor, said Hines' parole eligibility will be determined by the Maryland Parole Commission. William J. Kunkel, head of the commission, was not available for comment yesterday.

The new laws include a rule that defendants receiving a life sentence shall not be eligible for parole consideration until they have served 25 years, instead of 15 years as dictated by previous policy.

The legislation was introduced by a citizens group formed to push for stiffer sentencing after the conviction and sentencing of two men who killed Stephanie Roper, a 22-year-old college student from Prince George's County.

Stephanie Roper's mother, Roberta Roper, heard closing arguments in the Hines case on Monday and said she is still not convinced the new laws are tough enough. "These kinds of cases point out the need for a maximum life sentence," she said.

Under a revised 1978 Maryland death penalty statute, jurors must weigh aggravating and mitigating factors during a sentencing hearing.

No one has been put to death in Maryland since 1962.

The Hines jurors told attorneys from both the defense and prosecution yesterday that Hines' mental disorder--a mitigating circumstance--was more important than any other consideration.

During the sentencing hearing, a psychologist testified he believed Hines was a paranoid schizophrenic.

Jurors also said they were swayed by Hines' rambling, confused speech as he read nervously from the witness stand Monday excerpts from the Koran and "The Prophet." Hines has always maintained his innocence in the case.

Last June this same jury found Hines guilty of murdering Nakada, a University of Maryland student. Her nude body was found in the woods near her Hyattsville apartment shortly after the murder. She had been stabbed 40 times and parts of her body had been burned.

Hines had applied for a job at the apartment complex the day before the murder and was an early suspect in the case. He was not charged until last year when police found him serving time for a parole violation in Alabama. According to testimony during the trial, Hines called himself "the Angel of Death" and claimed to have had conversations with Adolf Hitler, among others.

Hines' attorneys said he was relieved to get a life sentence, though he showed little reaction in the courtroom. Melbourne told Hines she will arrange for him to return to Alabama to be near his relatives and to finish out his sentence there before coming to Maryland.