Sharon Klompus, a professional tutor who lives in Olney, was driving her 1979 Malibu Classic station wagon early last Friday and decided to turn on her rear window defogger to clear the morning mist. Then, she says, she smelled something burning. "I decided it was coming from my car and then I decided it was the defogger and I turned it off. Within five minutes, the back window and the frame exploded."

So, with her luggage area looking as if it were covered with 10 pounds of rock candy and with the frame of the shattered window hanging by a thread, Klompus drove into her Chevrolet dealer. "He said, 'Can I help you? and I said, 'I want you to come and look at my car,' and he came and looked at it and said, 'Oh, yes, we've seen a few of these.' And I said, 'And you didn't notify us that this could blow up?" At this point in her account, Sharon Klompus' voice was doing something known as rising.

"Then he said, 'Oh, it isn't a big deal or it's not a recall.' I don't know what he said. Whatever it was, it wasn't acceptable. The thing that I'm concerned about is that this is the season to start using defoggers and I'd hate to have this happen to anybody else. Little kids are in the backs of station wagons and if you don't know this is going to happen, you put little children back there, turn on your defogger, take them to school and the back window blows up on them.

"The service man told me this is not the kind of stuff that will cut people, but I said if it's being propelled, it will put an eye out," says Klompus.

It turns out that Sharon Klompus is not the only person to have her rear window shatter while she is driving down America's highways. It turns out, in fact, that the Department of Transportation received 39 complaints of this happening as of last June 3, enough to warrant an investigation. That investigation is still going on, but early on in the process, DOT found out from General Motors that it had received 180 complaints about the rear windows from owners. The cars involved are the 1979 intermediate station wagons, specifically, the Chevrolet Malibu and Malibu Classic, the Pontiac LeMans and the Grand LeMans, the Oldsmobile Cutlass Cruiser and the Cutlass Cruiser Brougham, the Buick Century Special, and the Century Custom. When it opened its investigation, DOT announced that it had reports of one accident, one fire and five injuries as a result of the shattering windows.

In it's press release, DOT stated that there is a wire grid assembly used to heat the rear window glass. "The failure appears to be caused by hot spots within the glass when the defogger is used." DOT warned that the principal dangers involve the risk of injury to small children riding in the back of station wagons and the risk of "driver distriction associated with sudden shattering of the rear window."

Joan Claybrook, head of DOT's highway traffic safety administration, further cautioned that the glass fragments are hot enough to burn a hole in the carpet covering the luggage area and urged that GM "conduct a safety recall to correct this problem before additional accidents or injuries occur."

But that's not what happened. GM issued a press released announcing that it was cooperating with DOT, and contending that, while the cause of the problem was still undetermined, "the glass did not explode nor was it propelled forward into the passager area" during laboratory simulation of the breakage.

GM said if felt the condition was "islocated," and predicted that "those vehicles which would incur tailgate window breakage have probably already experienced this problem."

That was in June. Hal Paris, a spokesman for the transportation department, said, in effect, it takes time to look into a possible safety related auto defect. Should DOT decide that a car has a safety related defect, it orders the manufacture to conduct a recall.

But while all of this investigating is going on, car owners like Sharon Klompus are driving around thinking their tailgate window is going to behave like a tailgate window. Furthermore, when the tailgate window shatters, it is not at all clear who should foot the bill. In Klompus' case, the dealer agree that she did not have to pay the $464 for parts, nor after she insisted, the $56 for labor. Harold Jackson, a spokesman for GM, said the company is paying for "some" of the cases.

Jackson points out that from a safety point of view children should never be riding in the back seat of wagons. All that is very true, but the point of the matter is that people do put children and pets in the backs of station wagons. Yet, short of a recall, there is no reliable way of making sure that owners of these 1979 intermediate station wagons know that their tailgate windows might shatter if they turn on their defoggers. There is no procedure such as an advisory letter that would tell car owners there might be a problem.

At this pount, no one even knows how many people have had their tailgate windows shatter. GM is compiling that information for the government, according to Jackson, and is holding fast to its position that there is "no unreasonable risk of accidents or injury as a result of this condition. . . . You relaize," added Jackson, "that this is out of some 87,000 wagons."

I'd like to see him tell that to Sharon Klompus.