The federal government is reopening its investigation into possible safety defects in metal wheels used on millions of trucks, campers and buses because they may cause tires to explode.

The National Highway Traffic Safety Administration said late last week it would reopen an earlier investigation into the special, multipiece wheels because of new data submitted by the Insurance Institute for Highway Safety. The institute cited 194 cases of multipiece wheel explosions since 1960, leading to 32 deaths and 129 injuries.

Multipiece wheels consist of two different parts that must be dissassembled for the tire to be mounted or repaired. The "rim base" provides primary support for the tire, while the "ring" serves as a flange and locking system. The lip of the ring fits into the gutter of the rim base and is secured when the tire is inflated.

According to the Insurance Institute, an independent non-profit research group, "if the components of a multipiece wheel are not perfectly aligned in the assembly process of it they become misaligned by any number of common occurences, including the normal operation of the vehicle, an explosion can occur, making the ring a lethal projectile."

"Reaction to the Insurance Institute's pettition came swiftly from the wheel manufacturers.

"There is no highway safety problem associated with property assembled and correctly maintained multipiece rims and wheels," said Michael Fay of the Firestone Tire & Rubber Co.

Goodyear Tire & Rubber said there were "no safety defects in the commercial truck rims and wheels," it manufactures either, but added that it was "a complex industrial component, one that must be carefully handled."

"Handled with care by skilled personnel," Goodyear said that "multipiece rims do not represent an industrial hazard. But there is a danger of accident during the mounting and dismounting of tires, rims and wheels."

In its report on the 194 explosions, the insurance institute said, 11 different designs of wheel produced by four major manufacturers were involved.

"What we're talking about us a design approach that is inherently defective, one that is literally blowing people's heads and limbs off," IIHS president William Haddon Jr. said recently.

In a press conference yesterday, Haddon called on NHTSA to set a safety standard that would, in effect, ban multipiece wheels from the road.

The Institute released films of two recent tests in which it deliberately exploded multipiece wheels to show potential problems with the tires.

One film showed a simulation of a serviceman changing a flat tire at roadside.

The exploding tire "acted like a land mine," Haddon said, hurling the locked ring into the dummy's throat and chest at a speed of more than 100 miles per hour.

The second test showed a father and son kneeling by a wheel of the family camper to inflate the soft tire. The wheel exploded, hitting both, with the locked ring hitting a dummy child's groin at more than 75 miles per hour.