A tour bus of Catholic school students from Massachusetts slammed into a low, stone overpass along the George Washington Memorial Parkway yesterday, crushing the roof and injuring several teenagers on a class trip, police said.

U.S. Park Police said the tour bus, owned by Eyre Bus Service Inc., was traveling south toward Mount Vernon about 10:30 a.m. alongside a second bus filled with students from St. Sebastian's School in Needham, Mass., when the crash occurred. The crippled bus traveled past the bridge, strewing debris on the road before coming to rest about 100 yards away.

Ten students, among the 27 people aboard the bus, were injured and taken to Inova Fairfax, Mount Vernon and Alexandria hospitals, where most were treated for minor injuries and released, spokeswoman Beth Visioli said. Two were held for observation and were reported to be in good condition last evening, Visioli said.

David Gusella, 16, of Framingham, Mass., said he was playing cards with his friends in the bus when he heard a "rumbling" and then saw the roof collapsing in "as if it was on a hinge."

"The roof dropped down and clipped the kid next to me on the head and knocked him into the aisle," Gusella said. "It was surreal. The glass was coming down like rain. You could feel it run over your face and over your shirt. Then the entire side of the bus was gone. You looked to the right and all you could see was the road. No roof, no windows, nothing."

Relatives and others who viewed the damage said it was astounding that more passengers were not hurt. One injured student's aunt called the scene "breathtaking."

The same overpass, at Alexandria Avenue, was struck by another tour bus in 1987, killing an elderly tourist and injuring dozens of others. In that case, the roof was sheared off the bus.

"He hit the bridge pretty hard. They're pretty lucky," said Lt. Warren Boyer, U.S. Park Police field commander, of yesterday's crash.

Boyer said signs on the parkway alert motorists to the height of the overpass -- 13 feet 4 inches in the center lane and 10 feet 2 inches in the right lane, too low for most buses. The bus driver was traveling in the right lane when the impact occurred.

Ron Eyre -- whose Glenelg-based Eyre Bus Service and tour company has operated local tours for 58 years -- said he could not comment on the cause of the crash while it was under investigation.

He said only: "The bus hit where the bridge curves over. [The driver] should have been in the middle, and he wasn't."

The parkway was closed in both directions for several hours yesterday as police investigated the crash. The Federal Highway Administration was also on hand to investigate possible damage to the overpass, police said.

William L. Burke III, headmaster of the all-boys school, said most of the 64 students had been dropped off by parents at school early yesterday before a flight to Baltimore-Washington International Airport for the school's annual junior class trip to tour historic sites around Washington.

"It's a bonding experience. . . . We've been doing it for a least 20 years," Burke said.

Mount Vernon was to be the first stop.

In the chaotic minutes after the crash, witnesses said, some youngsters walked around in shock, others escaped through the bus windows. Passing motorists stopped to offer towels to wipe away glass shards and blood.

"Nobody was crying. Everybody was in shock, wandering around. Everybody seemed really traumatized," said Andrew Dolan, 16, a St. Sebastian's student. Eventually, the school notified all the parents in Boston, some of whom sent relatives who live in the Washington area to check on their children at various hospitals. The injured students will rejoin their classmates to complete their Washington tour, Burke said.

Gusella said he felt lucky that he and several other students had been hunkered down over a pile of playing cards in the bus aisle, in the middle of a game of "Texas Hold 'Em" poker, when the bus hit the overpass.

"The roof hit the seat before it hit my head," Gusella said, adding that if he and his classmates had been sitting straight in their seats instead of bent over their card game, "we would have been fully exposed."

"Sounds like the good Lord was watching over them," the headmaster said.

Staff writers Elaine Rivera and Jay Mathews contributed to this report.

A student from St. Sebastian's School in Needham, Mass., is helped by Fairfax County rescue personnel. Behind them is the shattered roof of the Eyre Bus Service Inc. tour bus.Signs on the Alexandria Avenue bridge over the George Washington Memorial Parkway warn of height restrictions.Fairfax County firefighters remove an injured student, immobilized on a backboard, from the bus by way of a ladder.An investigator examines the tour bus wreckage. The aunt of one injured student who came to the crash scene called the damage "breathtaking."