The sentencing hearing of Howard Hines, a 29-year-old facing a possible death penalty for the murder of a Japanese student, goes into its fourth day Monday under unusual circumstances.

This is probably the first sentencing, court officials say, occurring under stiffer state sentencing laws, known as the Roper legislation, which went into effect July 1. Roberta Roper, mother of a murdered college student, spearheaded the legislation's lobbying effort and attended the first day of Hines' hearing.

One of the laws may even have had an effect before the sentencing hearing began. Testimony during the trial suggested that Hines may have been acting under the influence of the drug PCP. But because the law now says intoxication--by alcohol or drugs--may not be used as a mitigating factor during consideration of the death penalty, Hines' defense attorneys haven't introduced the idea of drugs during the hearing.

The defense maintains that Hines is mentally ill and should be institutionalized for treatment. The prosecution is asking for the death penalty because of the brutal nature of the murder and because of the violent behavior they say Hines has exhibited in the past.

Over the last three days, Assistant State's Attorney David M. Simpson has given the jury information it did not hear during the murder trial regarding Hines' extensive criminal background.

Simpson told the jury that according to investigations by the state, when Hines was 8 years old, he hit a child in the head with a brick. At age 15, Simpson said, Hines shot and wounded a schoolmate. In 1977, Hines pleaded guilty to raping a woman in Alabama, was sent to jail and paroled two years later, Simpson said. He then moved to California, the prosecutor added, where he was convicted of sexually molesting a child and assaulting another person.

Last month, the jury deliberated 25 hours before finding Hines guilty of the June 21, 1979, murder and attempted rape of Michiyo Nakada, 22, who was studying psychology at the University of Maryland. Nakada's nude body was found in the woods near her Hyattsville apartment. She had been stabbed 40 times in the chest and neck, 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 but was not charged until last year, when Prince George's police found him serving time for a parole violation in Alabama. Throughout the trial, Hines has maintained his innocence.

A statement from Michiyo Nakada's family is to be read to the jury next week--in line with another of the stiffer sentencing laws which requires the introduction of a victim-impact statement into a sentencing procedure.