THE TONSIL'S OF today's children are no different from those of a decade ago -- with an important exception: The incidence of surgical removal has declined by about 50 percent.

The reason is to be found in massive statistical studies that have found no therapeutic value -- though some risk -- in the indiscrimminate use of this medical procedure. As these findings have penetrated the medical profession, and have reached the attention of anxious parents, the decline in tonsillectomies has been prodigious, from 1.2 million operations performed in 1965 to 629,000 last year. In the opinion of many specialists, there are still too many tonsillectomies, but the downward trend is striking and is likely to continue as skepticism toward this one-time ritual of childhood becomes institutionalized in the practice of medicine.

Apart from the pain and cost that have been avoided, we think the decline warrants notice as an unfortunately rare example of an effective response to this country's epidemic of unnecessary surgery. According to a report last week by a House subcommittee, there were at least 1.9 million needless operations, of all kinds, in the United States in 1977, at a cost of over 10,000 deaths and nearly $4 billion. While such crisp statistics on an essentially hazy subject invite curiosity, it seems clear -- on the basis of scores of diverse studies -- that a serious problem does, in fact, exist. A case in point is to be found in the booming incidence of hysterectomies, which increased by 26 percent between 1968 and 1973, so that the rate here is now more than twice that of England and Wales.

While debate rages over how much is enough, what should be of concern is that the American medical enterprise is right now equipped with a number of institutions and mechanisms that could effectively contribute to preventing needless surgery -- but that these guardian devices are flabbily employed, if at all.

The ever-coming, but never-quite-on-line nationwide system of Professional Standards Review Organizations (PSROs) is designed to review the necessity, quality and economy of federally reimbursed medical services. But, while the administration earnestly declaims about the urgent need for cost-containment and quality assurance in medical care, the promising PSROsystem, with a few localized exceptions, merely stumbles along, six years after enactment into law.

Last year, the National Institutes of Health inaugurated a series of "consensus" meetings aimed at determining what is reliably known about lmany new and old medical therapies; and, as it turns out, quite a few of them -- such as tonsillectomies -- are based more on hunches than on firm clinical evidence. The findings of these meetings merit wide attention, not only among doctors, but also, -- perhaps especially -- among those who are on thereceiving end of medical attention, the general public. With some exceptions, however, the news media tends to ignore these important proceedings.

There are various other devices for getting at the complexities of the needless-surgery issue. Virtually all hospitals routinely review surgically removed tissue as a check on diagnostic quality. But medicine's old-boy mentality rarely permits disciplining of poor performers, and, as for publicly identifying them -- that's out of the question. Second opinions onlsurgery, a system that is yet to be disputed on any rational bassis, continues to inflame the mandarins of medicine, thought, fortunately, the concept is gradually seeping into the practice of medicine.

Given the unpleasantries of needed surgery, we can well do without the unneeded variety. The tonsillectomy saga is heartening in its outcome, but, regrettably, much of the evidence that led to a decline in the use of that procedure was long ago available, and ignored.

Medicine now possesses the analytical techniques and the organizational lmeans to accelerate the process of rational assessment of surgical procedures. But doctors have got to do it, or guess who's going to jump in and do it for them?