The National Highway Traffic Safety Administration has requested meetings with officials from BMW, Audi and Mercedes-Benz to discuss research with regard to the safety of side air bag systems they have in current production vehicles.

"We will express concerns about the data," says a NHTSA source who requests anonymity.

The agency met individually with several automakers over six months to discuss side air bags and to review the companies' research into the systems, especially with regard to out-of-position children in the back seat. The last meetings were held in January.

NHTSA officials called additional meetings after further reviewing air bag data from the three luxury German carmakers and after the Chicago Auto Show, where General Motors Corp. showed videotaped crash tests suggesting its side air bags are safer than some competitors'.

The additional meetings were to be held by the end of March. The source says it is not a formal investigation, as NHTSA does not yet regulate side air bags. The companies are cooperating.

Side air bags in front seats are becoming more common in vehicles, but now they are emerging in back seats for high-end luxury cars. The rear side bags arrive as American drivers are warned that children are safest when belted in the back seat. But if a child falls asleep leaning against a door, the explosive force of an air bag can be lethal.

The NHTSA source says the agency studied GM's side air bags and "didn't see any problems" with them, partly because they deploy more gently.

NHTSA is planning an April 19 public meeting for automakers and safety groups to discuss side air bags.