The National Institutes of Health has long devoted most of its resources to research performed on human beings or, when that is ethically objectionable, on animals most closely related to humans -- apes, monkeys and other mammals.

Now, however, a panel of the National Academy of Sciences has urged that the NIH devote more of its resources to finding alternatives to such traditional "guinea pigs" as monkeys, rats, dogs and, yes, even guinea pigs.

In some cases, the report said, the NIH could make just as much, if not more, scientific progress by studying "lower" animals, such as fish, clams, worms and microorganisms.

On the surface, the recommendations might appear to play into the hands of the increasingly militant "animal liberation" movement, which tends to focus its zeal on the species closest to humans in evolutionary terms. Some NIH scientists have been threatened with violence; many work in fear of bombings or break-ins.

In fact, leaders of both the NIH and the academy say the recommendations are not intended to deal with this problem and could lead to even greater use of mammals. The panel suggests that by neglecting to study lower species, which are simpler, the NIH may be missing opportunities to learn about basic biological phenomena that are common to all species but may be hard to recognize in more complex organisms.

Once those phenomena are recognized in lower organisms, it will be necessary to test for them in higher organisms before medical benefits can be extended to human beings. The panel also emphasized that in many areas of biomedical research it will always be necessary to use higher animals.

The recommendations apply to both the hundreds of intramural research projects at the agency's Bethesda campus and the $3 billion-plus in grants for thousands of other projects, mostly at universities.

Even before the academy released its report last month, the NIH had moved to adopt some of the recommendations by establishing a new section, called Biological Models and Materials Resources. Its first head is James D. Willett, who had been special assistant to Betty H. Pickett, director of the Division of Research Resources, which houses the new section.

Willett served as the NIH's project officer for the 21-month study, which the agency funded for just under $400,000. He also is project officer on a study by a different academy panel that is examining the nature and magnitude of lab-animal use nationwide.

The panel's recommendations emerged from a wide-ranging study of cases in which animal research began as basic science but, serendipitously, led to discoveries that benefited humans.

"The thing that really impressed us," said Harold J. Morowitz, a Yale biophysicist who chaired the academy committee, "was something that biologists have always talked about but rarely considered in its full implications: unity in diversity. This is what makes it possible to say that a snail or a bacterium can give you just as much information as rat or a monkey."

"Unity in diversity" is a century-old observation that, for all the obvious diversity in the living world, all species share common attributes, such as the basic structure within their cells.

This unity is, of course, the reason research on monkeys or mice can yield information about the human body. The academy panel reminds the NIH that the unity extends even more broadly and that, for example, the nerves of worms communicate in the same way human nerves do.

Because these alternatives are simpler to use and often cheaper, the panel said, they make it easier to learn what is happening biologically, speeding the day when humans gain the benefit.