A smoke bomb set off in a stairwell at Langley High School in Fairfax County yesterday sent 26 students and four faculty members to area hospitals, where two students were admitted because of difficulty breathing.

The others injured -- suffering eye, nose and lung irritations from the thick smoke -- were treated at Fairfax and Arlington hospitals and released, said Pam Weiger, spokeswoman for the Fairfax County Fire and Rescue Department.

The smoke bomb, described as a silver canister about six to seven inches long, was set off in a stairwell under the "Langley Calendar Now On Sale" sign and filled the halls with heavy smoke, according to observers. The school was evacuated and the injured were taken by school buses and ambulances to hospitals.

Other students filed into the auditorium or gymnasium for 1 1/2 hours before classes resumed.

The alarm was sounded about 12:15 p.m. and fire vehicles arrived just minutes later at the school at 6520 Georgetown Pike. Emergency vehicles happened to be in the area, according to Fire Chief Warren E. Isman. He said there had been no arrests.

Isman said the Langley incident was the second smoke bomb set off at a county school in the last few weeks.

A similar incident occurred at Lake Braddock Intermediate School in Burke. There were no injuries.

He said the violation is a felony punishable by up to five years in jail and a $10,000 fine, and students were being questioned by investigators yesterday.

"I'm concerned that this is a way of getting a little excitement into the schools," Isman said.

And there was plenty of excitement at Langley yesterday.

"Oh, it was awful. You couldn't see a thing," said school administrator Lynne Schwabe, who was trying to steer students back into classrooms. She was successful until a television crew turned on its bright lights, attracting a small mob of students.

"Get to your classrooms!" yelled a hall monitor. "Richaaaard!"

Schwabe said there was poor visibility because of the billowing smoke, and it took a little longer than usual to empty the school.

"People were running into each other," said Chris O'Donnell, 17, a senior.

O'Donnell said he and others were leaving Room 247, but there was smoke in the hall and they couldn't breathe so they returned to the room and opened the windows.

"Then the fire bell rang, so we all made a run for it," he said.

"I understand you have a list of names, and I'm missing a daughter," Myrna Wahlquist blurted out in the school's main office, which became a command post of sorts with phones ringing incessantly. Wahlquist's daughter was not among the injured.

Maikel Cigonii, 16, and Matthew O'Connell, 18, both of McLean, were admitted to Fairfax Hospital suffering lung irritation and bronchial spasms. They were listed in fair condition.