Two Montgomery County school employes and two children were injured, none seriously, in a rash of accidents between 3:30 and 4 p.m. yesterday involving county school buses, police said.

In the most serious of the three crashes, a county school bus driver and a teacher's aide were injured when a bus carrying two seventh-graders collided with a dump truck and struck a tree in Aspen Hill, according to county police spokesman George R. Ludington.

Driver Mary Cassidy, 32, of the 14000 block of Castle Blvd., Silver Spring, was listed in stable condition last night at Suburban Hospital. The aide, 51-year-old Daisy Maria Cardenas, 235 E. University Blvd., Silver Spring, was in satisfactory condition at Montgomery County General Hospital.

Ludington said a dump truck driving north on Layhill Road near Norbeck Road apparently skidded and fishtailed, glancing off the left rear panel of the southbound bus.

In a second accident, a pupil at Lucy Barnsley Elementary School in Rockville was slightly injured when a county bus driving on East Jefferson Street struck the front right fender of the car to its left while changing lanes to avoid another car whose driver had stopped to ask directions, Rockville police said.

The pupil, 11-year-old Jennifer Claude, of 57 Crossridge Ct., Germantown, a passenger in the car, was treated at Shady Grove Adventist Hospital after complaining of head pains and released.

In a third accident, a Potomac woman who was turning her station wagon from Seven Locks Road across traffic onto Tuckerman Lane struck an oncoming school bus.

The motorist, Carol Baker Wheeler, 39, of 11712 Charen La., was under observation last night at Shady Grove hospital. Wheeler was cited for driving while under the influence of alcohol, Ludington said. A 9-year-old girl who was riding with Wheeler, identified as Angela Foster, was treated and released, hospital officials said.