Considerable controversy has arisen over the issue of rear lap belts, much of it stemming from a 1986 report by the National Transportation Safety Board.

The report by NTSB -- an independent federal agency charged with investigating the causes of transportation accidents -- concluded that rear lap belts could harm passengers as well as help them.

NTSB officials said that as a result of their findings, they could not advise rear-seat passengers to wear lap belts.

That comment drew a heated response from parties promoting seat-belt use, including rebuttals from the National Highway Traffic Safety Administration, the agency within the Department of Transportation responsible for improving motor vehicle safety.

In brief, NHTSA argued that the NTSB study was based on biased research -- that the bureau's 26 selected crash cases were unusually violent and were bound to result in critical injuries and deaths, with or without seat belts.

Other studies -- notably by B.J. Campbell, director of the Highway Safety Research Center at the University of North Carolina -- supported NHTSA's claims.

The 26 NTSB crash cases "are so severe that neither lap nor lap/shoulder restraint systems could be expected to perform very well -- and indeed, neither did," Campbell wrote in a 1986 report.

Despite their criticisms, Campbell and other auto safety researchers agree that shoulder-harness belts generally are more effective than lap belts in crashes, and that lap-only belts can cause serious injury in high-impact frontal collisions.

But Campbell said that lap belts tend to be better than no belts, particularly in side-impact collisions where passengers could be flung through open doors.

NHTSA and the nation's auto makers encourage the retrofit installation of rear-seat shoulder harnesses in cars that don't have them.

Kits can be ordered through local auto dealers and installed at the dealerships.

Current prices on the kits range from $60 to $100. Labor costs, which vary, could add as much as $200 to the total.

Many people seeking the retrofit rear harness packages may encounter dealers who do not know about the kits, according to NHTSA spokesman Ron Defore.

In those instances, Defore said that customers are urged to contact the local zone offices of the auto manufacturer.

If the zone offices can't help, Defore said that customers should call the local NHTSA safety hot line at 366-0123. For customers outside the area, NHTSA has a toll-free number, 800-424-9393.