''One, two, buckle my shoe'' soon may give way to ''one, two, buckle my seat belt'' as being among the first lessons in American toddler talk. Thirty-eight states plus the District of Columbia have enacted laws mandating the use of car restrainer chairs and other security devices for infants and all small children.
All but nine of those states passed the laws within the last year and a half. And similar measures are pending in at least five other states, several of which are expected to pass them within the next few months.
Before long Congress, too, may be getting in on the act through highway-safety funding incentives to aid states in strict enforcement of their car-restraint laws.
Two such proposals have been filed in the House and one in the Senate in recent weeks and a fourth is being readied.
An estimated 1,500 children under age 5 are killed or severely injured annually in accidents involving the car in which they are riding, reports the National Safety Council.
Although the number of such fatalities for 1981 is not yet available, National Highway Traffic Safety Administration (NHTSA) estimates that two years ago there were 633 vehicle passenger deaths among those aged 4 and below across the United States. In 1978 the total was 726, and in 1979 and 1980 it was 698.
Until last year less than a handful of states had child-restraint laws in effect. Thus, those close to the scene question to what extent the reduction stems from new laws.
Boosters of child-protection measures generally agree that loss of life and severe injuries to infants and toddlers could be substantially reduced through use of restrainer chairs and seat belts.
Robert Scherz, chief of staff of the Mary Bridge Children's Hospital in Tacoma, Wash., has conducted a study of the effectiveness of such safety devices over the past 13 years. He concludes that ''any kind of a child restrainer is better than none in a car crash.''
Based on his investigation of some 51,500 Washington road accidents involving passengers under age 5, he projects that the number of infants and tots killed in auto crashes ''could be reduced about 90 percent'' with properly used restraints.
Dr. Scherz says he is enthusiastic about newly approved legislation in his state under which, starting next January, parents and guardians carrying babies under age 1 must have them secured in a child-restraint seat. Other small children up to 5 years old will have to be similarly held by a tightly fastened seat belt.
In Washington, as in all but three of the other states with child-restraint laws, violators are subject to fines. Generally, those fines help pay for administering the child safety program. In some instances, this includes buying restrainer seats for parents unable to afford them.
In Tennessee, where the law has been in place for the past five years, state troopers carry extra child safety devices with them to loan to parents caught on the road without restraint equipment, explains Robert S. Sanders, public-health officer for Rutherford County, Tenn. Under his prodding, Tennessee became the first state in the Union to adopt a car child-safety statute in 1977. Dr. Sanders says that compliance in his state is improving, but there is ''still a long way to go.''
Sanders notes that in each of the past three years, the number of infants and small children killed in car crashes on Tennessee roads has shrunk by better than two-thirds, from 22 in 1979 to only 6 in 1982.
Keys to the success of such statutes, he contends, are ''a good educational program, vigorous enforcement, and a loaner program to provide child-restraint seats for parents who need them.'' Some 8,000 tickets, 3,600 last year alone, have been issued by Tennessee state and local police since 1979. He emphasizes that the intent of such laws is not punitive, but to provide greater child safety.
In North Carolina, where the car child-restraint law is in the midst of a three-year trial, official reaction is also enthusiastic.
William Hall, research associate of the University of North Carolina's Highway Safety Institute, reports that the number of infants and toddlers under 2 killed or seriously injured in auto accidents has declined from 19.5 per 1,000 vehicle fatalities or serious injuries to 14.1. The law also is credited with helping reduce the number of crash death and injury victims between ages 2 and 5 in the state, Mr. Hall observes.
Car crashes are the major cause of accidental deaths of small children, observes Nancy Berk of the National Safety Council.
Kathy Weber of the University of Michigan's Transportation Research Institute says that although many of the state laws require that only children under age 1 or 2 need be held in special restrainer seats, ''as long as the child fits, we recommend their use'' before graduating on to seat belts.
Children are safer in the rear seat of the car than in the front seat, she adds.
Contributing substantially to the near tidal wave of car child-restraint laws over the past two years has been the strong backing of groups like the National Safety Council, the Insurance Institute for Highway Safety, the American Academy of Pediatrics, the American Medical Association, and the Highway Users Federation, as well as NHTSA.
Opposition to the car child-safety statutes revolves largely on the parental rights issue - requiring mothers and fathers to provide for the safety of their small children in a certain way, rather than leaving it to their discretion.
Concern over forcing parents who cannot afford it to buy special toddler seats or infant holders, which is raised by some, has been considerably removed by programs in most states, because fines are used to provide the necessary equipment.
Since raising money is not the goal, several states frequently refund fines when the motorist cited shows proof the restrainer has been bought and is in place.
Child-restraint legislation is pending in Iowa, Louisiana, Missouri, Pennsylvania, and Texas. Minnesota, whose car child-safety law went on the books two years ago, but without provision for fines for violators, appears to be in the process of so strengthening its legislation.
This would leave only Kansas and Oklahoma with penalty-free measures for protecting infants and toddlers while riding in in the family auto, notes Catherine Yoe of the Highway Users Federation.