Gymnasium bleachers collapsed at a high school this morning in an assembly, injuring as many as 52 students, the authorities said.

Hospital officials said none of the injuries appeared to be life-threatening. The steel bleachers gave way at 8:11 A.M. at Maurice J. McDonough High School, said Lieut. David Gladwell of the Charles County police. The students were all 11th graders, school officials said.

Injuries ranged from bumps and bruises to broken legs and ankles and some suspected spinal injuries, said Fire Chief Ken Chaplin, whose forces were called in to help.

The staff and students have been absolutely wonderful. They reacted like clockwork,'' said Linda Dent-Brown, administrative assistant to the superintendent at the county Board of Education.