Once the stethoscope and knee thumper were the staples of a doctor's testing equipment. Today doctors are more likely to use a host of complex procedures or sophisticated machinery. And new technologies are continually being introduced.

But is a CAT scan of the chest really better than the stethoscope? How does the physician judge the safety and effectiveness of these new procedures or devices? Are the new methods any better than the conventional procedures?

The fact is that many old and new technologies have not been properly evaluated and, in some cases, patients may be exposed to ineffective and even harmful technologies, say some leading health technology experts such as Clyde Behney of the congressional Office of Technology Assessment and Dr. Seymour Perry of the Georgetown University Institute for Health Policy Analysis.

A treatment used for ulcers in the 1950s is a textbook example of a remedy that became popular before it was proven. Based on animal experiments, a leading surgeon from Minnesota developed a method that nearly froze part of the stomach to stem flow of gastric acid. But after more than 10,000 patients had undergone gastric freezing, other researchers began to question its true effectiveness and tested it more extensively. They concluded that the procedure was virtually ineffective.

As technology has become more complex and subtle, it has become more difficult to determine when a certain technology is safe, effective and worth the risks or costs.

Last month, for example, a government study reported that it is not clear whether a relatively new method of dialysis -- continuous ambulatory peritoneal dialysis, or CAPD -- is really cheaper or as effective as the more conventional method even though the medical community widely believes both are equally good. According to the OTA study, although 8,000 Americans have undergone CAPD, no rigorously controlled clinical trial has yet been conducted to compare the two methods.

Today's technologies also pose ethical and economic dilemmas because of their enormous expense. The medical extravanganzas surrounding recent artificial heart recipients raise questions about who should receive one and who should pay the cost.

Technologies are not being evaluated because there is no national organization to do the job, say Behney, head of OTA's health program, Perry, deputy director of the Georgetown Health Policy Institute, and others. No single forum exists where health experts can hammer out the difficult scientific, economic, ethical and social issues related to health care.

The complexity of these issues is compounded further by the fact that they pit powerful and competing groups against one another. The National Center for Health Care Technology of the Department of Health and Human Services -- once charged with evaluating technology -- was phased out in 1981, in part because of opposition by the American Medical Association and the Health Industry Manufacturers Association.

The center, which was created in 1978, scrutinized the clinical value of a variety of widely used therapies. It reviewed the state of the art of coronary bypass surgery, concluding that the surgery was lengthening lives; it set guidelines for the use of dental X-rays; and it outlined when cesarean sections should be performed.

The center's conclusions also helped to cut health costs. According to one study by the University of California of Los Angeles, the center's recommendations potentially saved the Medicare program at least $100 million a year by recommending certain procedures not be covered, such as blood treatment called plasmapheresis, which was being used to treat rheumatoid arthritis. The center concluded that the technology had not been proven effective.

But in the process of choosing some technologies and procedures over others, the center made enemies. The AMA forcefully argued that the center had overstepped its bounds by taking cost into account, which was traditionally the domain of the patient and physician. The AMA charged that the center was dictating the practice of medicine.

The medical device trade group objected when the center put together a list of technologies it considered experimental. A product classified as experimental was, in the eyes of industry, "the equivalent of being on a hit list," Perry says. Industry accused the center of trying to stifle innovation.

Together, the two powerful organizations successfully lobbied federal officials to kill the center, including Sen. Orrin G. Hatch (R-Utah), chairman of the Labor and Human Resources Committee. "Hatch opposed it and it was the kiss of death," says Perry.

Since then, the federal government and the private sector have been trying to fill the gap. Congress expanded another federal agency -- the National Center for Health Services Research -- to include "Health Care Technology Assessment," but it has a considerably narrower focus than the older National Center for Health Care Technology. The new agency only reviews a particular technology when requested by the Health Care Financing Administration, which runs Medicare and Medicaid. Similarly, OTA can only study a technology when Congress asks for a review.

NIH draws experts together to examine technologies, but it tackles a limited number of technologies a year. Dozens of major private health organizations have also started up or expanded their own technology assessment groups -- including AMA, the American College of Physicians, Blue Cross-Blue Shield, the Health Industry Manufacturers Association and the American Hospital Association. But NIH and private sector organizations rarely, if ever, take the cost of a technology into consideration when assessing technology. And the medical specialty groups are subject to charges of bias.

Medical technology assessment by the government and private sector have been "fragmented," said a Senate staff aide involved with health policy. Despite the spate of recent activity by private groups, "no one is doing what the national center was intended to do," says Behney of OTA.

" Medical technology assessment lost its identity" when the center was eliminated, says Stuart Schweitzer, a professor at School of Public Health at the University of California at Los Angeles.

The fractionated system that has evolved is seriously flawed, according to a lengthy OTA report published after the original center folded. Potentially obsolete procedures are often not studied because newer, more glamourous technologies grab researchers' interest first, said the 1982 report, "Strategies for Medical Technology Assessment." "High quality, objective assessments . . . are rare," it stated. Many of the evaluations by various groups are "informal, overly subjective, group-generated notes and are not based on a rigorous assessment of the scientific evidence."

Furthermore, said the report, many of these groups unnecessarily duplicate each other's work and choose projects that only reflect their own concerns.

David Tennebaum, director of the medical necessity program at Blue Cross-Blue Shield headquarters in Chicago, says that the multiplicity of groups is valuable. "Although everyone misses the center, the various groups go a long way" toward achieving the original goals of the center, he says. Several organizations may do the same assessment, he says, but "everyone brings something different to it."

Blue Cross and Blue Shield evaluates a procedure based on its coverage implications. The hospital association will look at a technology with an eye more toward the potential to write off the cost of the equipment, Tennebaum said.

Many health care leaders agree that, at the very least, a national group is needed to serve as a clearinghouse for the mix of information being generated. Congress this fall is expected to establish such a group within the Institute of Medicine. The new group will also pinpoint what technologies should be studied and how they should be studied.

Says Behney: "It will do a lot to temper potential bias concerning what gets studied."