A 24-year-old University of Maryland senior was killed early yesterday apparently after trying to jump from a third-floor dormitory bathroom window to the adjacent roof of the dorm porch, campus police reported.

John O'Reagan, a 6-foot-2, 220-pound mechanical engineering major from Oxon Hill who would have graduated next month, fell onto an outside concrete stairwell at about 2:30 a.m., hitting his head, police said. The stairwell runs between the basement and the first floor of Cambridge Hall, so O'Reagan fell between three and four floors, police said.

O'Reagan was taken to Leland Memorial Hospital and was pronounced dead shortly after arrival at 3:03 a.m., according to police.

O'Reagan, who played on the dorm's intramural football team, was last seen by other Cambridge residents at about 2:15 a.m. but according to Cpl. Don Smith there were no eyewitnesses to the incident.

Cambridge Hall is part of a residential quadrangle that sits in the north section of the College Park campus just east of Byrd Stadium. Students often go out on the front porch roof, usually through third-floor dorm windows, to relax and watch people coming and going at the computer science center or on the playing fields in front of the dorm, residents said yesterday.

When dorm rooms are locked, students get to the roof from the bathroom window about three or four feet away.

"I never had any trouble jumping to the roof ," said a student who asked not to be identified. "But today, I looked up there again and said, 'Geez,' that's a long jump."

Investigators from the campus police force spent most of yesterday trying to piece together where O'Reagan was before the fall.

Thomas J. deSeve , safety and security manager for the university's department of resident life, described O'Reagan as "very well-rounded and very well-liked in his dorm."

According to David Medhoff, resident director for the dormitory, O'Reagan had just passed a physical exam qualifying him for Navy flight training, and "I know he was pretty happy."

"One minute you have a student who's got everything going for him, realizing his aspirations," Medhoff said, "then the next minute it's gone."