It is the world's largest "clinical research center," a place where the medical laboratory meets the patient.

Starting today, by act of Congress, the giant research hospital at the National Institutes of Health will be known as the Warren Grant Magnuson Clinical Center, for the Washington Democrat who has been its friend.

Translate "friend" into "moneyman." Until he lost his seat last November, "Maggie" was the longtime chairman of the Senate health appropriations subcommittee, and he usually gave NIH more than any president asked.

Today, too, the new Magnuson Center will officially spawn an addition, another product of congressional friendship. It will be dedicated by Health and Human Services Secretary Richard S. Schweiker, who was also a friend of NIH when he was on the Hill.

The addition will be a giant, $100 million set of out-patient clinics and laboratories with the rather awkward name of the Ambulatory Care Research Facility. Together, the 29-year-old hospital building and the new clinics should be the laboratory for the medical care of the next century.

The clinical center is only one part of the vast NIH campus in Bethesda. There are also 11 institutes dealing with various diseases and parts of the human anatomy. With a 1981 budget of $73.6 million, the center accounts for a little more than a tenth of the $668.2 million spent on the NIH campus. (Most of NIH's total $3.6 billion budget finances research at hospitals and universities around the country.)

The center is the institute's very own, highly unusual hospital. The older building is split down the middle, with patients on one side of each floor and research laboratories on the other. Doctors and scientists go from one to the other, testing and applying new findings.

The care is all free--that is, paid by the taxpayers--for patients referred by doctors all over the country. Under the rules, a patient must fit into a "research protocol" or ongoing program, which often tests one kind of treatment against another.

Out of this marriage of care and research has come the first successful chemotherapy of a cancer (choriocarcinoma); "combination chemotherapies" using batteries of drugs against leukemias and lymphomas; work on the chemistry of mental illness, leading to new drugs; and practical discoveries and new treatments in arthritis, heart disease, high blood pressure, genetic disorders, infections and other conditions.

Most of this work was done by studies on hospitalized patients. But medical care has been changing since 1952, when the hospital building was first occupied. More and more diseases, even cancer, can be treated on an out-patient or ambulatory basis, that is, on patients who walk in, get some attention and leave.

This is the main reason for building the new facility, Dr. Mortimer Lipsett, the center's director, said yesterday.

"The clinical researcher," he said, "is the man who stands with one foot in the laboratory and one foot at the bedside. He takes the new information from the lab and tries to bring it to the patient.

"Today, however, he doesn't always have to do this at a bedside. And the fact that we have this new facility will also enable us to look at many less life-threatening but still important conditions."

Among them: asthma, allergies, many mental conditions, eye diseases, nerve disorders and pain. Pain alone will be the concern of one entire new clinic.

To help treat and study patients with these conditions, the new 14-story facility will have extensive patient-testing laboratories and many X-ray and other machines to look under the skin at illness. Like the older building, the new facility will have both basic research laboratories and patient clinics on the same floor.

The older, 504-bed hospital has 1,246,860 square feet of usable space. The new facility will add 685,000 square feet. Together, they will handle 7,600 hospitalized patients and 100,000 out-patient visits a year at the start. Ultimately, the new facility may accommodate 250,000 out-patient visits a year.

So far, only some cancer laboratories have been established in the new building. But the first patient clinics and other labs will be occupied before the end of the year, and the building should be in full use by mid-1982.

To some extent, the pace will depend on the still uncertain fiscal 1982 appropriations, and the extent to which NIH and the Magnuson Center feel President Reagan's call for a 12 per cent cut in 1982 spending plans.