The families of three Japanese teenagers who were injured when they fell out a back door of a Metrobus in March filed suit yesterday seeking $11.5 million from Metro and the bus and door manufacturers.

The suit alleges that Metro, General Motors Corp. and Vapor Corp. were negligent in the maintenance, design, manufacture and installation of the door, which burst open as the bus was starting around Chevy Chase Circle at 4:57 p.m. March 20.

Metro has not completed its investigation of the incident and would not comment on the allegations in the lawsuit, said spokeswoman Beverly Silverberg.

The three girls and 19 classmates from the Ursuline Academy in Hachinohe City, Japan, were visiting Washington during a 2 1/2-week tour of the United States. The group was riding a Metro bus to the 4-H National Council Headquarters, where they were staying, after sightseeing.

The three girls were standing in the rear aisle as the bus started around the circle. One lost her balance and grabbed at two companions. All three fell against the double rear doors. The left door burst open, thowing all three to the street.

Toshie Nakajima, 17, was critically injured when she fell under the wheels of the bus and was dragged 24 feet. She required head surgery, suffered a broken ankle and a shattered knee, received 16 skin grafts to her left leg and lost all movement in the limb, said her attorney, Joseph H. Koonz. The leg may yet have to be amputated, he said. A scar remains on her forehead at the hairline.

Her family is seeking $10 million in damages, claiming she has suffered physically and financially from the accident. She was unable to graduate with her class this year and faces dim marriage and career prospects in a society that shuns the disabled and disfigured, Koonz said.

Nakajima wrote to her attorney from Japan two months after the incident, describing her daily medical treatment: "I am doing my best to cope with this painful therapy. The scars in my leg are getting better. But to tell the truth, I am very reluctant to go back to school with this crippled leg."

Reiko Higashino, 17, was critically injured with a fractured skull and abdominal injuries. She lost some of her hearing in her left ear, Koonz said. Her family is seeking damages of $1 million.

Kaori Fukumura, 17, was treated for minor injuries. She now has a scar on her mouth and continues to receive dental treatment for her injuries, Koonz said. Her family is seeking $500,000.

After the incident, Metro officials found a clean break in the metal housing of the bus door's motor above the door. Metro has not released the results of metal tests to determine whether the part was cracked before the incident.