They like to cloak these things in the mantle of science and bind them with soft compassion, but anyone who has glimpsed a brawling children's playground will understand.

Cancer, the bully, came first and took over the swing set. But Heart was unhappy and demanded its own corner of the schoolyard. That upset Lung, which laid claim to the kickball, and inspired Blood to commandeer the quoits.

Tooth and Brain, meanwhile, stayed off to the side and becamecame teacher's pets. Eye was struggling to become a big boy and so was Arthritis. tThere was more, but you get the picture.

What we have here, in the metaphor of the playground, is the contentious story of the National Institutes of Health.

For the billions it spends and the impact it makes on the well-being of man, NIH remains a mystery in the alphabet soup of government agencies. FBI, IRS, CIA, USDA -- everyone knows who they are. But NIH?

From a wooded, 300-acre campus in Bethesda, NIH oversees the federal research effort to unlock the mysteries of life and disease. Several thousand scientists in Bethesda and many thousands more around the country are supported with NIH money, which this year is more than $3 billion.

There are flowing phrases to describe the exciting stuff of biomedical research, but it probably is put best and most simply by Dr. Donald S. Fredrickson, the NIH director.

"It is the search for reality," he said recently. "The basic thread is to try to continue to understand what is reality, the nature of man . . . Through that remains a desire that the work will stand and affect the quality of life, giving everyone a fair shot."

But the price of all this is huge and the pressure is on NIH researchers to do more, to do it quicker and get it to the patient sooner, and to do it as inexpensively as possible.

Out of the political pressures -- the same sort of hurly-burly as the playground -- NIH has evolved into 11 institutes devoted by name to a full range of human disorders and biological studies.

"It cannot be said that NIH developed in accordance with anything that looked like a plan," Robert M. Bock of the Federation of American Societies for Experimental Biology (FASEB) recently told Congress. "It could not even be said the NIH evolved. It has to be said that NIH simply accumulated."

That accumulation is wryly known throughout the biomedical research establishment and on Capitol Hill as the handiwork of the "Disease of the Month Club," which is an allusion to Congress' penchant for creating new institutes every time a disease lobby squeaked, coughed or sighed.

The rash began in 1948, with creation by Congress of the National Heart Institute. Two weeks later, the National Institute of Dental Research came into being. Neurological Diseases and Blindness appeared in 1950, along with Arthritis and Metabolic Diseases.

In time, lung and blood diseases were added to Heart. Eye Research became a separate institute. Others were formed, with Environmental Health Services (1969) and Aging (1974) the newest of the 11.

From that comes a picture drawn tersely at a recent House health subcommittee meeting by Rep. Barbara A. Mikulski (D-Md.). She saw a "good" NIH image of Nobel prize winners working earnestly and a "bad" image of "fiefdoms, petty politics, and old-boy network a full-employment program for Ph.Ds."

Within NIH, each of the institute directors is fairly anonymous. Fredrickson, a physician and widely honored laboratory scientist, is the one who must make the whole machine hum.

This is the time of year when Fredrickson emerges from his dimly lit office, carpeted with his own Oriental rugs and adorned with his private art, to become the public voice of NIH.

As the process requires, he has trooped up to Capitol Hill to explain President Carter's fiscal 1981 budget for NIH, which proposes about $3.6 billion. That figure stands to shrink, maybe as much as $300 million, by the time Carter's new budget-balancing act finds its equilibrium.

House and Senate Appropriations subcommittees already have heard Fredrickson and the directors of the institutes defend the 1981 proposals. Public witnesses are now pressing the subcommittees for more money for their favored institutes.

The hearings groan with pain. Witnesses weep as they describe diseases that afflict loved ones. "These hearings," Fredrickson said in an interview, "are a reflection of the anxieties of man. We all want cures . . . Our job at NIH is not to be indifferent, but we've got to translate those desires into practicalities. Each of these unveilings (of cure) comes at its own time."

No one even pretends very much anymore that the constitutional process of funding puts a fair light of scrutiny on NIH. With about 90 percent of NIH's research appropriations going "off-campus," a huge scientific-interest network has developed, pressing for more funding. Advisory boards, some of them dominated by disease lobbyists, recommend higher funding for their respective institutes.

Over the long haul, this has meant congressional budget increases systematically each year. But inflation also has meant that the institutes have treaded water since the mid-1970s.

Director since 1975, Fredrickson has sensed a day of reckoning drawing nigh for NIH. It may be now, in fact, with Carter and Congress in a budget-slashing mood.

"There are certain new realities," Fredrickson said. "The emergence of the congressional budget committees, inflation, more competition for the federal money.

"There seemed to be a time when these would converge and Congress would not 'correct' a presidential budget by increasing it. Two to three years ago we began to prepare for this time."

NIH's way of dealing with the new realities was to try to stabilize the number of research grants at 5,000, thus ending the annual up-and-down of grant approvals and sending a message of certainty to the scientific community.

Toward that goal, Carter's Office of Management and Budget and the president himself decided to produce the first budget in eight years proposing to spend more than Congress appropriated the previous year. They decided to put $139 million extra into the basic research program.

"We had to get a floor under the research grants, which oscillate from year to year. It makes long-range projects difficult and it is a damned difficult railroad to run," Fredrickson said.

But he is catching Holy Ned from Congress and research scientists because this meant another important outlay, grants to institutions to train young new research investigators, would not be increased.

FASEB, with 20,000 members, and the Association of American Medical Colleges, 126 institutions that rely heavily on the training money, are distraught over that, as are some legislators.

Fredrickson has not been in government since 1953 and on the fringes of big-league politics without learning how to cut for the basket and slam-dunk an idea.

"We wanted to see how we could rationlize and find a way Congress and the executive branch could maintain the stability of a basic science system that was not growing that much anymore," Fredrickson said.

Boosting research meant curbing training. With a White House favoring more basic research and an OMB that historically opposed training, Fredrickson didn't have to think too hard.

"You don't go to the OMB with training as your goal," he said. "But we made an honest effort on training and I asked the department [Health, Education and Welfare] for more training money, but at a secondary level."

That, of course, did not get past either HEW Secretary Patricia R. Harris or OMB. Fredrickson got the additional money he wanted to stabilize the research grants.

Some senators railed at Fredrickson over the training cuts. But Reps. William H. Natcher (D-Ky.), chairman of the House subcommittee, went out of his way to tell Fredrickson the panel thought he had done it exactly right.

With Carter, OMB, Harris and Natcher on his side, Fredrickson had scored important points. And that, friends, is playground hardball.