Ahmad Nowrouzi killed his pregnant 26-year-old girlfriend "in a heat of passion" on July 1, 1989, a Montgomery County Circuit Court judge said yesterday in finding him guilty of second-degree murder.

Judge Peter J. Messitte declared that the behavior of Nowrouzi, 27, of Gaithersburg, was "reprehensible, awful and callous" when he abandoned the body of Marlene D. Forrester in a car at a remote parking lot at National Airport. Her body was found by a passerby 17 days later.

Messitte, who delivered his verdict to a hushed, crowded courtroom after a six-day non-jury trial, declined to provide specific reasons for his decision.

The judge said he found "little credibility" in Nowrouzi's accounts to police of what had happened at Forrester's Gaithersburg apartment the morning that she was killed. "His line was too persistent, too cool, too deliberate," Messitte said.

However, Messitte said he concluded that Nowrouzi, who had a stormy two-year relationship with Forrester, "acted without premeditation" in the woman's death. "He acted in the heat of passion," Messitte said.

The judge declined yesterday to say how he thinks Forrester died, although he said his verdict "turned on the physical evidence, logic and other facts under consideration."

Testimony during the trial centered on conflicting opinions from medical experts about the cause of death. A Virginia coroner had ruled after an autopsy that Forrester died of strangulation caused by a broken hyoid bone, a U-shaped bone at the base of the tongue.

But defense attorneys challenged the autopsy report and presented testimony from a well-known pathologist that strangulation was "medically impossible" because of the absence of blood in the hyoid bone.

However, the prosecution produced as a rebuttal witness a District medical examiner who testified yesterday that dark discoloration in the hyoid bone indicated that "some blunt force" had caused bleeding.

Messitte said that "there is no question that the defendant had a motive to end the life of Marlene Forrester."

In closing statements yesterday, Assistant State's Attorney Kathleen Toolan said Nowrouzi, who managed a gasoline station, killed Forrester because he was under pressure from his family to participate in an arranged marriage to a woman from his native Iran.

During a tape-recorded interview with detectives, Nowrouzi said Forrester attacked him with a knife during an argument at her apartment. Nowrouzi told police that Forrester was cut on the arm and that he attempted to drive her to a hospital.

On the way to the hospital, Nowrouzi said, Forrester began to slump in her seat and was choked by her seat belt when he slammed on the brakes to avoid a truck.

"I saw her slide down first," Nowrouzi said in the taped statement. "I tried to undo the seat belt. I tried. I tried. I couldn't get the seat belt."

Nowrouzi told police that he then panicked. "I was so scared," he said. Nowrouzi told detectives that he sat for three hours in the parking lot of a Rockville restaurant before returning to Forrester's apartment to remove incriminating evidence. He later drove to National Airport's Satellite B parking lot and left Forrester's body in her car, in a reclining position and covered with carpet.

Barry Helfand, the defendant's attorney, argued that the prosecution had relied on speculation, adding: "The state has not proved a homicide."

Messitte said Nowrouzi's actions after Forrester's death were a "coverup" for the crime. "The acts were reprehensible, awful, callous . . . the kind of thing we hope never to see in our society," the judge said.

According to court testimony, Nowrouzi left several messages on Forrester's answering machine shortly after her death and lied to her family and friends when they asked about her disappearance.

Prosecutor Toolan said in her closing statement that Nowrouzi returned twice to the airport parking lot because he was curious about whether Forrester's body had been found.

Nowrouzi, who faces up to 30 years in prison, is scheduled to be sentenced Oct. 10.