This may come as a surprise to those who know her, but my daughter the 5-year-old has grown up under restraints: her ride home from the hospital was one of the last times she was in a car without being strapped into a car seat or seat belt. As a result, she automatically fastens her seat belt when she gets into a car now, and if I should start pulling out of the driveway before she was finished, she lets out a wail that would curl your hair.

This year, however, she began kindergarten and rides every morning on a school bus that has no seat belts. Roughly 50 percent of her traveling is now done in a manner that may not be as safe as it could be and which signals her that seat belts aren't necessary. Given enough time on a school bus, she could get out of the seat belt habit with no trouble at all.

She is a member of the first generation of American children who have done most of their growing up in an era when car restraints for children became widespread.

Five years ago, the sight of a baby or young child sitting in his mother's lap in the front seat of a car was all too common. So were the instances in which those children were thrown through windshields or crushed against dashboards during accidents.

In 1981, when only six states had child passenger protection laws, the National Safety Council estimated that only 10 percent of the children under five rode with correctly used restraints. Each year, the council estimated, 850 children were killed in car crashes and another 57,000 were injured.

Now, 49 states have passed laws requiring restraints on young children in cars. A Department of Transportation study of 19 cities for the second quarter of this year found that 43.5 percent of all children 1 to 4 years old were in child restraints as were 68.2 percent of the infants.

Only 14.3 percent of all drivers, however, buckled up.

The next logical step for advocates of child safety was to look at the nation's 390,000 school buses.

The National Transportation Safety Board has recommended mandatory installation and use of seat belts in vans used as buses and in special use buses, but it has made no recommendations on seat belts in full-size buses, which, as of 1977, have been built to stricter safety standards designed to compartmentalize and pad children against impact.

The board is currently studying more than a dozen school bus accidents to determine whether seat belts would have lessened the extent of injuries, according to Suzanne Stack, a transportation board safety specialist.

"So far, we cannot see any clear pattern emerging that lap belts would have made that much of a difference.

"We find that many times children have come out of severe accidents amazingly well. The new safety standards seem to be performing with large conventional school buses.

"The big fight," says Stack, "is brewing over the habit formation question."

Rep. Peter Kostmayer (D-Pa.) introduced legislation last year that would provide $10 million a year for three years to help states pay for getting belts on buses. "It's fairly controversial," says Kostmayer.

"People who are in the school bus business feel it would create a lot of supervision problems for the drivers, belts would become instruments of war between youngsters and the bottom line is the expense," estimated at $1,000 to $1,500 per bus.

While he believes they would make the buses safe, he also argues that not having belts on buses confuses children about the safest ways to ride in vehicles. "It destroys any effort we have to get them to use belts in cars if they don't also have them on buses."

In 1983, 3,300 students were injured in school bus accidents, and 10 were killed while they were on the bus, according to the National Safety Council. School bus accidents account for 0.2 percent of all accidents; cars account for 76.5 percent. Relatively speaking, the nation's school buses are the safest vehicles on the road.

But they transport 21.5 million children to and from school each day. Logic, and a smattering of knowledge about human nature, strongly suggest that as children grow up and spend more and more time on buses, they will gradually get out of the habit of using belts in cars, particularly when relatively few adults set an example. This, more than the safety question, may be the best argument of all for belts on buses.

It would be a pity for a generation of children who have started out right to break a habit that can save their lives.