In public service ads and jingles, the message from the government and auto industry safety experts is clear: Young children are safer riding in the back seat.

But that advice may not be true if parents are driving older cars, namely the 50 million autos still on the roads that were built before 1988.Those vehicles don't have air bags, and few have shoulder belts in the back seat.

For children who outgrow child seats but still need booster seats, the safer spot in these older cars actually may be the front passenger seat, where there are both lap and shoulder belts to secure the booster.

A senior official of the National Highway Traffic Safety Administration concedes that the government's advice about putting children in the back seat may be misdirected for those with pre-1988 cars.

"Any time you make something too simple, then in some cases it is wrong," said James Nichols, acting associate administrator for traffic safety programs.

At issue is the safety of children weighing 40 to 60 pounds - roughly ages 4 to 8.

The booster seats for such youngsters require both a lap and shoulder belt to meet government safety requirements for head and neck injury protection. But one-fourth of the cars on the road were built before 1988, when back-seat shoulder belts were a rarity.

There are no booster seats on the market for children between 40 and 60 pounds that can be used with just a lap belt.

"If there's no rear-seat shoulder belt, then for safety I would move the child to the front seat, properly restrained in a booster seat," said Nichols.

Some other safety advocates agree.

"We have a big product gap on booster seats," said Joseph Colella, who offers training on child passenger safety. "It is not always possible to put a child in the back seat properly re-strained."

Deborah Steward, editor of Safe Ride News, a newsletter for health and safety professionals, said: "My bottom line is, it's much more important to get children restrained than to make sure they're always in the back seat."

Safety advocates say children who outgrow a child seat should be placed in a booster seat, the next step in protection, before graduating to a seat and lap belt alone at age 8.

Passenger-side air bags have been blamed for the deaths of 51 children, prompting both the government and automakers to begin efforts to persuade parents to put kids in the back seat.

Young children wearing just a lap belt in back risk head or abdominal injuries.

Drivers can get back seat shoulder belts installed in old cars. But Nichols acknowledges many people would not do that because of the cost and time required. Consumer Reports recently said the price ranges from $250 to $460 per belt.

But there are divisions in the safety community on this issue.

Some physicians note the back seat is generally one-third safer for children, and given the problems with misuse or lack of use of child seats, they would prefer children sit in back.

"In 20 years as an emergency-room physician, I haven't seen a child seriously injured by a seat belt," said Dr. Joseph Zanga, president of the American Academy of Pediatrics. "I have seen literally dozens of children killed because they were not wearing a seat belt."

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ADDITIONAL INFORMATION

Child car safety

Booster seats for children weighing between 40 pounds and 60 pounds require both a lap and shoulder belt to meet government safety requirements for head and neck injury protection.

A look at the differences between a child sitting in a booster seat and a child without one:

With booster seat - Shoulder belt properly on shoulders.

Without booster seat - Shoulder belt hits face

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Different ages, different seats

Guidelines for selecting the right restraints for children in autos according to National Transportation Safety experts:

INFANT SEATS: Children should be in an infant seat facing the back of the car until they are at least 1 year old and weigh at least 20 lbs. The neck muscles of infants are insufficiently developed to ride facing forward. In cars with passenger side air bags, the infant seat must be in the back seat.

CHILD SEATS: Children weighing 20 to 40 lbs., roughly ages 1 to 4, should be in a forward-facing child seat with its own restraint system for the child, such as a harness that runs across both shoulders and buckles between the legs. The auto's seat belt system is used to secure the child seat.

BOOSTER SEATS: Children should move to a booster seat when they outgrow the child seat, roughly between ages 4 to 8 and when they weigh 40 to 60 lbs. A booster seat properly positions the auto's lap belt across the child's pelvis and the shoulder belt across the chest. Some booster seats are made for children weighing 30 to 40 lbs.