FOUR PEOPLE DIED as a result of a head-on car F collision in Montgomery County Sunday evening. The victims were a married couple who were seated in the front seat, their 14-month-old daughter who was in the front seat with them and their 4-year-old son who was seated behind the driver. A 5-year-old boy wearing a seat belt in the back seat survived, as did the 16-year-old driver of the second car.

Nancy Moses of the Montgomery County police said witnesses told police that the baby girl was hurled through the windshield when the two cars collided. "She was apparently being held by the mother," Moses said.

Moses said no one knows whether her brother and parents were using seat belts. Cpl. Phillip Caswell, another police spokesman, said investigators believe they still would not have survived, and they don't know whether the baby would have survived if she had been in a car seat. But it is conceivable that had she been properly restrained she would not have been hurled through the windshield and might have survived.

The evidence that seat belts and child restraints reduce the number of fatalities and the severity of injuries in traffic accidents is overwhelming. The arguments against compulsory use of seat belts for adults center on questions of individual freedom and privacy. That's an issue for another day. Those arguments do not, and should not, have anything to do with society's obligation to protect young children. They do not have the ability to make up their own minds whether to wear seat belts or sit in child restraints. Moreover, adults persist in endangering children's lives day in and day out by allowing them to travel unrestrained in automobiles.

About 850 children under 5 years of age die in auto crashes each year and more than 57,000 of them are injured, many of them permanently, according to the National Safety Council. Less than 10 percent of the children in this age group ride with seat belts or car seats, which means the vast majority of young children are crawling around freely in moving vehicles, with the potential of disrupting the driver's concentration and turning into human projectiles if their car is hit.

Carrying a child passenger on your lap in the front seat of a car is the most dangerous way for a child to travel, says Patricia Goldman, a member of the National Transportation Safety Board. The safest way by far is to strap a child into a car seat that is secured with safety belts and bolted down in the back seat of the car. "The whole purpose is to have the person ride the accident down with the car frame rather than floating free in the car and banging around inside," she says.

When a person is hit, the reflex reaction is for the arms to go out in a flailing motion, says Goldman, which means that an adult holding a child in the front seat releases the child. If a person sees the crash coming and holds onto the child, the adult takes the child with him and the child becomes the first part of the battering ram through the windshield, or the child is trapped under the force of the adult against the dashboard.

More than 100 pieces of legislation were introduced in 41 states during the past year to protect child passengers, according to the National Safety Council. Laws requiring restraints for children have now been passed in nearly a dozen states. Some states allow fines to be waived if the parents appear in court with proof they have purchased a car seat.

Tennessee, with active lobbying from the state's pediatricians, passed the first law in 1978 requiring children under 4 to be riding in approved child restraints. From that time until mid-March 1981, only one child who was properly restrained died in a crash, and that crash, in which the seat-belted mother also was killed, was described by investigators as nonsurvivable. By contrast, 53 children under 4 who were not restrained died during that time. When the law was first passed, it had exempted infants held in the arms of an older person, but that exemption was eliminated after several tragic accidents involving such children.

Gene Roberts, Tennessee's commissioner of public safety, told an international symposium on occupant restraints this past July that studies in that state showed that use of restraints has increased fourfold in recent years, although about 70 percent of people still fail to use them. The Highway Patrol began a vigorous educational and enforcement campaign in September 1979 and child restraint use doubled. The Highway Patrol started a fund-raising effort to buy car seats for violators who could not afford them.

Tennessee's efforts to persuade the public to use restraints voluntarily were "remarkable ony in their lack of persuasiveness," Roberts said. While we may not like the idea of being forced to put young passengers in restraints, it seems clear that voluntary compliance and information dissemination haven't worked. If parents will not do what is necessary to ensure the optimum safety of their children, then it is the proper role of the state to step in.

Had the legislature of Maryland not killed three child restraint bills last year, at least one more child might be alive today.