Robert Gitlin was a 16-year-old senior at Springbrook High School in Silver Spring who enjoyed camping, rock climbing and rappelling, a mountaineering technique that involves sliding down a rope to descend a steep incline.

Since there were no mountains near his home, Gitlin and his friends would rappel from the pillars of a Capital Beltway bridge over Northwest Branch, a stream in Silver Spring.

Yesterday, Gitlin died of head injuries he suffered Sunday when he hit rocks under the bridge while swinging from a rope.

The bridge is between the Beltway's University Boulevard and New Hampshire Avenue exits. In the past, when Gitlin rappelled from it, he would climb up one of the supporting pillars, tie his rope to a half-inch-thick steel girder at the center of the bridge and then slide down the rope onto rocks that were about 100 feet from the water's edge.

On Sunday, Gitlin decided to do something different. After he climbed up and tied his rope to the girder, instead of sliding straight down the rope, he climbed to one of the pillars and swung out.

First, he swung away from the pillar, then back toward it, all the while descending.

"He was traveling very fast," said Tim Clark, 16, of Silver Spring, a childhood friend of Gitlin's who was watching from the ground. "His legs were outstretched. His feet hit the rock and he slipped forward and then his head hit the rock. When I got to him his eyes were wide open but he was unconscious."

A man who had been fishing nearby called an ambulance, and Clark phoned Gitlin's parents. Gitlin was taken to Suburban Hospital.

Gitlin, who had had lessons in rappelling about two years ago in Great Falls, went to the bridge Sunday with Clark and another friend, Bill Foster, 16, both students at Springbrook High. It was the sixth time in two years that the three had gone rappelling under the bridge.

They were equipped with rappelling gear: gloves, climbing boots, and a brand new rappelling rope that cost $80.

Gitlin decided to go first. When he announced that he was going to swing from the pillar, Clark was worried, he said yesterday.

"I told him, 'You've never tried this before,' and then, when he went anyway, we kind of said to ourselves, 'I hope we're not witnessing his death.'"

Clark said he did not think Gitlin had intended to slide down the rope while he was swinging, "but the force of gravity pulled him down."

Gitlin and Clark had planned to go rappelling in Colorado after graduating from high school.