They were driving east early yesterday morning on Maryland Rte. 108, a narrow, unlighted stretch of highway in northern Montgomery County, when their car left the road and careered 300 feet before it struck a tree and burst into flame.

The four teen-agers inside, police said, had just returned from a Frederick, Md., bar. All were either critically injured or too dazed to move. But Rte. 108, where 11 persons have died in automobile accidents since January 1980, did not claim another life, thanks to a Damascus man who fought off a nightmare memory to pull them from the burning automobile.

"I can tell you this: If he hadn't been right there and pulled those kids out, they wouldn't be alive right now," said police spokesman Phil Caswell of the rescue that occurred on what is known as the most deadly road in Montgomery County. "He did a fantastic, courageous thing."

Charles (Dewey) Hudlow was driving home alone, westbound in the 4500 block of Rte. 108, when he witnessed the crash. Hudlow stopped and raced to the car. "It was just a horrible thing," said a badly shaken Hudlow yesterday. "It was just blazing.

"The seats were mashed up against the dashboard and the floorboards were catching fire. I couldn't get the doors open and that really shook me up. "There was a girl inside who was dazed and didn't give no reaction. I just pulled her out the window." Hudlow suffered first- and second-degree burns on his hands.

An unidentified motorcyclist arrived and pulled the victims Hudlow had rescued into an open field across the road in case the car exploded. But the flames prompted more bad memories than fear in Hudlow, whose daughter Cynthia was nearly killed in a house fire six years ago.

"She went through hell . . . It's the second time I've been through this. You never get over it," Hudlow said, breaking into sobs. "That's what I had on my mind the whole time. I'm glad they all got out. I'm glad it's all over with."

The entire rescue took less than four minutes, Hudlow said, but the smoke became so thick that he could only grope blindly for the last rear-seat passenger before he finally grasped his hand. He didn't know until later that two of the girls he rescued were friends of his own children.

Rescued from the fire, but listed in critical condition at Suburban Hospital yesterday were the driver, Mark Manning, 19, of Bel Pre Road, Wheaton; Cynthia Bandy, 18, of Sundown Road, Laytonsville, and Brian Claggett, 19, of Bowie Mill Road, Olney. Listed in good condition at Montgomery General Hospital was Anna Shipley, 18, of Wedge Way Drive, Gaithersburg.

No charges have been placed and police spokeswoman Nancy Moses said that investigators were initially attributing the fault of the crash to driver error and are awaiting the results of blood alcohol-level tests.

"It's a real bad curve right there," said Hudlow. Still, it remains a mystery why Rte. 108 has earned the nickname "Killer Highway." Police and state highway officials agree that there are several roads in the county with more dangerous curves, less smooth surfaces and sudden hills.

"I can't understand why there are so many accidents. Evidently there's just a phenomenon," said resident engineer Edward Wrzesinski of the Maryland State Highway Adminstration, who said that a recent study of the highway determined that no changes should be necessary. Even more striking, said Caswell, is the fact that most of those killed on 108 have been from the area and familiar with the road.

The road has picturesque sycamores hugging its edges, and is a smooth, clearly marked, two-lane highway that runs parallel to the northeastern border of Montgomery County. Its most dangerous aspect are the trees and utility poles, often only a few feet from the road. According to Wrzesinski, once a driver makes a mistake, "there's no shoulder for recovery."

Many of its victims are killed after running off the road and striking trees or utility poles, said Caswell. Three of the 11 simply fell asleep behind the wheel and crashed. Some of the crashes have occurred in broad daylight, on straight sections of road in clear, dry conditions.

"There's nothing wrong with the road . . . the drivers aren't paying that much attention . . . If you make a mistake there's no place to go," said Caswell.