A 17-year-old Coolidge High School student described by his principal as a "very mannerly, nice young man" was arrested in his affluent Washington neighborhood yesterday in connection with the shootings of two elderly women in their Silver Spring homes over the last two weeks.

Police said that robbery was the motive in both the May 31 murder of Rose Blanco, 68, and the June 10 armed robbery of Louise R. McKenna, 61.

Kevin George Scott of 1933 Tulip St. NW, in the comfortable "North Portal" neighborhood about a mile from the two women's homes, was arrested at his house about 6 a.m. by metropolitan police.

Scott, a tall, husky youth who appeared in D.C. Superior Court yesterday afternoon wearing pale bluejeans and a dress shirt, waived extradition and was transported by deputies to Montgomery County where he will be arraigned today in District Court.

Otis Thompson, Coolidge principal, said that Scott did not graduate from the school with his classmates last Friday - the date of the McKenna shooting - because he had failed a chemistry course. While he and others described the youth as a "nice" person, he was said to have been a frequent truant.

A county police spokesman said police have warrants charging Scott with the Blanco murder and the McKenna shooting.

County police spokesman Phillip B. Caswell said money was taken from the Blanco home and a purse containing cash was taken from the McKenna home. "Physical" evidence at the scene of both shootings led them to the suspect, he said.

Rose Blanco was shot in the back of the head about 11 a.m. as she was washing her living room window. There was no sign of forced entry to her home. Louise McKenna was wounded in the head when she surprised a burglar in her living room upon returning home from work at about 7 p.m., police said. The burglar apparently entered her home through a window.

The incidents left the Silver Spring neighborhood badly shaken, coming on top of a rash of assaults on women and burglaries.

Thompson said he got to know Scott about two months ago when he called Scott's parents to the school 'to discuss the youth's frequent truancy. "He wasn't just skipping one class - he was skipping school entirely," the principal said.

Scott, Thompson said, "didn't give any reasons" for his absence from school. "He just said he would improve." The principal's office had not received any complaints about the youth's truancy in recent weeks, Thompson added.

Scott's parents seemed concerned about the youth's truancy, Thompson recalled, but they had not been aware of it before their meeting him at school.

Nathaniel Scott, his father, operates a real estate firm at 6400 Georgia Ave., according to court documents. Helen Scott, the youth's mother, is retired from the State Department, a neighbor said.

"He had the best personality of any of the kids his age in the neighborhood," said Charles Dean, who lives next door to the Scotts. "He would come around and say 'Can I cut your grass?' or 'Can I do anything for you?'"

Jean Fox, who lives across the street, said she remembered often seeing the youth cleaning his parent's lawn and washing the family car.

One neighbor described the parents as concerned about their son's discipline, "in contrast to some families who just don't care what their kids do."

"They were parents who were interested in their son," the neighbor, who asked not to be named, said. She recalled how she would see Kevin riding his bike and playing basketball with the neighborhood kids when he was growing up.

Scott went to church every Sunday, according to his next door neighbor.

Scott has lived for the past 13 years in a neighborhood that is home to many high D.C. government officials and federal government employees.

The neighborhood, which contains mainly single-family homes with large lawn and yard areas, was one of the first integrated neighborhoods in the District, attracting wealthy, highly placed blacks and whites.