Just as the first splitting of the atom beneath the University of Chicago squash courts in 1943 led inexorably to the Los Alamos flats, so the discovery in 1953 of the DNA molecule - life's "blueprint" - has led to Room 215 in building 500 at this former center of the Army's chemical and biological warfare program.

The building doesn't look like much, just a non-descript, pale yellow stucco affair that might be confused with similar structures here were it not for the green and white 550 sign to the left of the door.

One would never guess that the room on the second floor houses the first of the nation's level P-4 laboratories for research with recombinant DNA - the combining of bits of the deoxyribonucleic acid of one form of life with the DNA of another.

But then there was never anything external to indicate that Army researchers were fooling around with deadly diseases like anthrax in the same room, assessing the "safety" of further experiments with them as agents of biological warfare.

The anthrax is gone now, and within two weeks it will be replaced in Room 215 with experiments in genetic engineering, for that is what work with recombinant DNA is, whether the genes being engineered are those of man, mouse, or is now the case, viruses and bacteria.

Experiments with recombinant DNA have been divided into four categories, according to their hypothetical biological hazard.

The facilities in which the experiments are conducted carry classifications from P-1 to P-4, depending upon the level of "containment" they provide. Room 215 is a P-4 facility, one approved by NIH as meeting NIH guidelines for the most potentially dangerous experiments.

The first to be carried out in the room will begin by April 1 and are planned as "risk assessment" experiments designed to determine if the accidental escape of recombinant DNA from the lab could really lead to a biological or ecological disaster.

The experiments will involve taking DNA from polynoma virus, which will by itself cause disease in mice, and recombining it with an extremely weakened form of E. coli bacteria to see if the bacteria will then cause polynoma virus in the mice. If the mice are not infected, that will indicate that the E. coli shields the polynoma DNA, researchers say.

Yesterday for the first, and theorretically the last time, the National Institutes of Health opened Room 215 for a media walk through.

First the members of the press were treated to what can only be termed a recombinant DNA sales presentation, complete with slides and a movie, with much emphasis on the hope that research with recombinant DNA will solve the mystery of cancer and little discussion of the moral and ethical questions raised by opponents of such research regarding man's tampering with and restructuring forms of life.

In groups of about 10, reporters were led past protesters carrying signs asking "Who Should Play God?" and "Do The Ends Always Justify The Means?" and through the front door of building 550.

In the first floor hallway the group was divided in two by sex, with the men heading for the stairway through the men's locker room and shower and the women going through the women's facility.

The path from the outer to the inner locker room leads through an air-locker, with the pressure inside the airlock lower than that outside, thus assuring that no air - and no recombinant DNA - moves from inside the building to the world beyond.

The tour groups were led up a dingy staircase in the 28-year-old building to the second floor and Room 215, a room of about 400 square feet containing interconnected, gas-tight, cabinents.

The laboratory is, in essence, a box within a box. The outer box is the building and the inner box is the area beyond the airlock. All experments will be carried on inside the gas-tight stainless-steel and plastic boxes. Workers carrying out experiments inside the boxes will reach into them through rubber gloves attached to the fronts of the boxes.

Just as all air beyond the airlocks flows toward the interior of the area, all air in the small stainless steel boxes flows inward, theoretically further preventing the possibility of a disaster.

The negative air pressure has not yet been turned on, and the lab is not being used.

In addition to the reporters passing through Room 215 yesterday there was one group of inhabitants there - a few dozen fuzzy brown mice blissfully unaware that by April 1 they will be the citizens of a brave new world.