A miniature train that runs through Lake Fairfax park near Reston derailed yesterday afternoon, tossing about 20 adults and children into the lake and injuring at least 11 of them.

Authorities said three of the injured were admitted to Fairfax Hospital for overnight observation. Most of the injuries were cuts and bruises, according to a hospital spokeswoman.

The manager of Lake Fairfax park, Michael Kane, said the miniature five-car train with 30 persons aboard was following its normal course at about 2 p.m. yesterday when it came down a slight embankment and crossed a tressel. "At this point, the third car rose up somewhat and then that car and the last two cars went over toward the lake," Kane said.

Kane said the train was traveling at 18 mph at the time of the accident. "That's slow for that area. It normally would have been going 20-to-21 mph," he said.

The driver of the train, 16-year-old Daphne Massa, has been employed as a seasonal worker since May. She was unavailable for comment.

Three adult passengers on the train, however, offered accounts that differed from Kane's. They agreed in separate interviews that the train was going dangerously fast when it came down a small hill after picking up passengers at the ticket booth.

Floridian Robert Bussey, who had taken a friend's 18-month-old child for the train ride, said the train accelerated as it came down the hill toward the lake.

"We were going at a pretty good clip and I thought to myself that this is too fast for a kiddie ride," he said an hour after the accident. As he spoke he held the child, whose leg had been cut. His left pant leg was rolled up above a cut on his shin.

"She (the engineer) blew her whistle as we came down that hill and I decided to grab hold of the baby. Just then the car tipped and we flew into the water. We rolled out of the car together but I lost hold of the baby. He landed between the rocks. When I found him, I dragged us both up on the bank. He was crying but okay," said Bussey.

Several adults who were riding in the forward cars remembered scrambling to safety as they heard screams around them.

Tina Busenberg was sitting with her 3-year=old son, George, directly behind the engineer. "The ride was like a roller coaster and going way too fast," said Busenberg. "I saw smoke as the train came to a stop. I grabbed George and we climbed out. I looked back and all these people were in the water and hurt. People were screaming and babies were crying."

Gladys Hayes and her three nieces and nephews were riding in the second car of the train. She too said that the train was traveling too fast when the accident occurred.

After she and her charges scrambled from the upright car, Hayes said she went to find the driver of the train. "I said to her that she was going too fast and she said to me that she couldn't slow it down," said Hayes.

Fairfax County police are investigating the accident. They said that, at this point, there is no indication of negligence on the part of the driver. Parts of the derailed train cars will be sent to a lab to help determine the cause of the accident, they said.

Back at the ticket booth where the train tickets are normally sold a hand lettered sign was taped with two band-aids to a post.It said: "Train is closed."