FOR SOME TIME now, we have been watching with considerable interest the dispute between two leading consumer protection groups - Consumers Union and Health Research Group - over the safety and utility of ionization smoke detectors. The argument, like any squabble between two like-minded groups, is fascinating. But his one has some other overtones. The product in dispute - systems that warn people against fires in their homes - is important. And the difference in the approaches of the two groups suggests the dangers that lurk out there when public interest groups push their expertise too far.

It all began in mid-September when the Health Research Group, which is affiliated with Ralph Nader's Public Citizen organization, denounced ionization smoke detectors because they contain a radioactive agent. It called them "mindless and dangerous" and urged that all four million of them then in use be recalled and destroyed. At the same time, Consumers Union, an organization that has been testing products and proving consumer information for 40 years, was readying and a report calling these detectors safe and highly useful in giving early warning of some kinds of home fires. The article recommending the use in homes of an ionization detector as well as one of the photoelectric type appeared in October's Consumer Reports. And the fight was on.

Dr. Sidney M. Wolfe, director of Health Research, told Consumers Union that it had not carefully considered questions of safety and efficiency, had failed to test for radiation leaks under certain conditions, and had ignored other nuclear-related hazards. He contended that even an official of the Nuclear Regulatory Commission "had conceded that the NRC found no inaccuracies in our report." He concluded that the devices subject workers and residents to the risk of harmful radiation. "The issue," he said, "is not how much radiation is released by why this extra amount of radiation exposure is necessary at all." Underpinning his argument were the fact that photoelectric smoke detectors sense smoldering fires faster than ionization ones and the assertion that since 75 per cent of home fires start out as smoldering ones, there is no need for another kind of detector.

Now, charges of that type are body blows when they are aimed at an organization like Consumers Union, whose stock in trade is the accuracy of its testing procedures. So it was not surprising when it returning the fire in its January publication. It said Dr. Wolfe's fears are "unwarranted" and his conclusions "are wrong." The second largest cause of home fire deaths, it said, are open blazes which photoelectric detectors generally ignore while ionization ones do not. As to the amount of radiation, Consumers Union insisted that the data show the detectors produce so little that there is "virtually no hazard." It said that the Health Research Group's warning against using these detectors, if followed by the public, "could lead to tragic consequences including the possible loss of hundreds of lives." And it quoted the same NRC official as saying that the Health Research Group's report "was inaccurate in that it left out anything that would have tipped the balance against the HRG's viewpoint."

We are sure this is not the last word. The language in Consumer Reports is a direct challenge to the thoughtfulness and care with which the Health Research Group evaluated these devices. But at the moment, it seems to us that Consumers Union is pretty far ahead. Its data make a substantial case that these detectors are not dangerous in normal use and do provide a substantial amount of protection that other detectors do not provide. The findings of the Nuclear Regulatory Commission support those safety conclusions. But you can judge for yourself by reading both reports.

The thin ice that it seems to us the Health Research Group is one results from its quick response to one particular threat to life - radiation - without weighing the degree of danger against the benefits to be gained. This same approach to consumer safety problems has appeared again and again recently in the arguments advanced by some other fairly new public interest of organizations. It arises either because they are so eager to reduce one particular threat that they fail to weigh the plusses and minuses or because they need something new every once in a while to keep them going. In either case, the results are the same - an undermining of their effectiveness. That, it seems to us, is going to be a growing problem for organizations which are created to push specific public-interest programs. It is quite easy for them to slip over the line which the public sees as dividing special-interest groups from public-interest groups.