Two men have been arrested in the Monday slaying of an 18-year-old man who was seeking to thwart an attack on his fiancee and her mother at Iverson Mall in Hillcrest Heights, Prince George's County police reported yesterday.

Rolf Richard Seiferth was shot while struggling with the assailants in the shopping center parking lot and died a short time later at Greater Southeast Community Hospital, according to police and witnesses.

Police said Kenneth Guinyard, 23, of 4654 Hayes St. NE was arrested in the mall parking lot not long after the shooting. Charles William Wade Jr., 23, of 1318 Dunbar Oaks Dr., Capitol Heights, was arrested later that night at his home. Both were charged with first degree murder, placed in the county jail and will be arraigned in court today.

According to police and others at the scene, two men surprised Seiferth, his girlfriend, Chris Lowe, and her mother, Jean Lowe, as they were about to get into the Lowes' car. Seiferth struggled with one of the men who then shot him once in the head before running away. Seiferth was pronounced dead at Greater Southeast Community Hospital a short time later.

Yesterday, Chris Lowe, 17, also of Camp Springs, recalled that the three had been Christmas shopping at Woodward and Lothrop just before the incident.

"Our car was the last car at the end," she said, tearfully. "It was dark. Mom got into the car and unlocked the passenger side. Somebody grabbed my hair and pushed me into the back seat . . . . He said, 'Get in the car, we're going for a ride.' "

A second man was on the driver's side of the car, Lowe said, but neither man asked for their wallets or money. She said she did not know the assailants.

The younger woman said the man standing on the passenger side had a gun and was trying to push Seiferth away from the car. While she screamed at the man not to shoot, "Ricky Seiferth started hitting him hard and fast." Lowe said she was fishing in her purse for a knife when she heard the gunshot and saw Seiferth fall. "He saved my life . . . . I want everyone to know he was a hero," she said.

Seiferth, the only child of Frank and Mary Knoell, was known in the family as "Pooh Bear." He would have turned 19 on Christmas Day. He graduated from Crossland High School last year and was a part-time student at Prince George's Community College.

He recently started working for a construction firm and "he wanted to stay in the job and be a carpenter," Mary Knoell, 38, said yesterday.

She described her son as a popular and outgoing young man who was protective of his friends. He and Chris Lowe were planning to marry this summer, she said.

Police said they knew of no motive in the incident.