LEAD: The police today arrested a teen-age suspect in the shooting of four students outside a high school here Thursday.

The teen-age suspect in Oregon reportedly brought a gun to school on Wednesday.

Officers continued the chase, racing with guns drawn through crowds of tourists and evening diners, and arrested the teen-age suspect a few blocks away.

The killings were the latest in an alarming number of murders involving young teen-age suspects in the city.

As the investigation continues, a picture emerges of a suburban world where adults had only superficial understandings of the lives of the two teen-age suspects.

The film also looks on as adolescent arrogance, while not a criminal offense, helps one of the teen-age suspects possibly dig his own grave.

In all, seven teen-age suspects broke free in three separate incidents, officials said.

Seven students were injured and at least three teen-age suspects were being sought, the authorities said.

(In one telling scene, three teen-age suspects leaf through a book of mug shots as if it were a high school yearbook.)

The police were seeking two other teen-age suspects, both believed to be in Mexico.