The National Highway Traffic Safety Administration yesterday urged the makers of child safety seats to make them safer, challenging them to go beyond the minimum safety standards now set by the government.

In a toughly worded letter sent to manufacturers, the NHTSA said that "many restraints have been engineered to barely comply with some of the most safety-critical requirements of the standard, rather than being designed with larger compliance margins." It chided manufacturers--none of them named--for trying to escape recalls, passing safety tests only by narrow margins and allowing safety-related defects in some of their products.

At the same time, the agency offered a special incentive to manufacturers that exceed the standards: a public rating system that would tell consumers what companies bested their competitors on safety.

By law, the agency cannot demand that manufacturers go beyond the rules that now exist, but nothing stops it from asking manufacturers to do more on their own.

"The bottom line is, those who exceed the standard should have a way to make the public cognizant of it," NHTSA Administrator Ricardo Martinez said in an interview.

The NHTSA estimates that there are more than 5 million child safety seats in cars and trucks, and their use has grown over the years so that 60 percent of children under the age of 5 are in some type of child restraint, up from about 11 percent in 1980. In the past two years, use of the seats has grown by 27 percent as parents have responded to national safety campaigns exhorting them to put their children in correctly installed safety seats.

The NHTSA said it believed that with the growing awareness of the benefits of safety seats, parents would appreciate the five-star rating system that the agency is considering. It would be much like the NHTSA's new-car assessment program, which awards stars based on how auto manufacturers exceed minimum crash standards. In the case of car seats, dummies strapped into the seats would be crashed into barriers at speeds higher than under the current standard.

The NHTSA's letter, which was not publicly disclosed but was sent to the presidents of each car-seat manufacturer, urged them to exceed current safety standards and to order recalls willingly.

"With the safety of our nation's children at issue, mere compliance with the minimum requirements of the standard is not enough; minimum standards should not be the most in safety design that manufacturers provide," the letter said. "When products are engineered with narrow compliance margins, the level of safety risk increases, even if the product is in technical compliance with the minimum standard."

The agency did not single out any one manufacturer or suggest that any particular car seat was unsafe. In other words, the companies passed performance tests most of the time for determining the crashworthiness of the seats in accidents, the flammability of materials used in their manufacture, labeling, instructions and the type of crash dummies used to test the seats.

But Martinez pointed out several serious failings that clearly prompted the letter.

"We are dismayed by the attitude of some child restraint manufacturers toward compliance failures, and an unwillingness to conduct safety recalls to remedy such noncompliances," the letter said. Research on the issue done by the NHTSA revealed "a lax attitude" on the part of some manufacturers that has resulted in what the agency calls "non-compliant" child restraints that might allow the head of a child to move too far forward in an accident or a mislabeling that doesn't warn parents of the dangers of air bags.

Since 1990, there have been 74 recalls of child safety seats, involving 19.6 million seats. There also have been six recalls of seats built into cars and vans by auto manufacturers, covering 311,512 seats.

The letter said that some companies have tried to convince the agency that problems uncovered are inconsequential and don't fundamentally affect the safety of the child. Under the law, manufacturers do have the right to make a case for not ordering a recall.

The Juvenile Products Manufacturers Association, which represents the seat manufacturers, said it strenuously objected to Martinez's characterization of manufacturers as not stepping up to do recalls. Association spokeswoman Kathleen Baier said it was more important to educate parents about getting their children into car seats, instead of scaring them about recalls that address minor, non-safety issues.

Paul Charland, director of risk management for Fisher-Price Inc. in East Aurora, N.Y., said his company is "open to the idea of advancing the ball . . . to create incentives for manufacturers to collectively improve performance."

Other manufacturers did not return calls, or said they had not yet read the NHTSA letter.

Safety experts said most car seats are well made and some are even overdesigned.

Phillip Haseltine, who headed two national panels on car-seat safety, said most seats protect children in accidents even when parents don't install them correctly. "I wouldn't feel uncomfortable recommending any brand of seat to a parent," he said.

CAPTION: NHTSA chief Ricardo Martinez pointed out serious failings.