Tonight at 8, public broadcasting's premier science program, "Nova," presents the first of two one-hour segments on the war against cancer. "Nova's" results are mixed, but then, so are the successes of the war.

This week's program -- on WETA (Ch. 26) tonight and on WHMM (Ch. 32) Thursday at 9 p.m. -- is devoted to the experimental use of the natural biological substance interleukin-2, about the hoopla surrounding this first major immunological approach to fighting cancer and to its failure to provide the instant cure a nai ve and desperate public read into its early notices.

Interleukin-2 is a protein that acts as a messenger between elements of the body's immune system. It can "tell" certain white blood cells to turn into cancer killers. It is made in minute quantities by the body, but with the help of bioengineers, researchers at the National Cancer Institute and now at about 30 centers around the country, have been able to obtain -- as one researcher says on the program -- probably "more interleukin-2 than has been made in the history of mankind," surpassing all the IL-2 made naturally by all the people who have ever existed.

"Nova" producers began this program months ago, centering on Boston's Tufts-New England Medical Center patients at the advent of the IL-2 program there, but not overlooking the program's experimental roots at the National Cancer Institute in Bethesda where its first victories seemed to portend a genuine breakthrough.

Dr. Steven A. Rosenberg, NCI oncological surgeon, discovered that removing blood cells from a cancer victim's body and "activating" them with genetically engineered IL-2 offered a potentially ultimate weapon against that individual's cancer when the newly activated cells, called Lymphokine-activated killer cells, or LAK cells, were restored to the individual.

Some early successes catapulted Rosenberg and his team to instant fame -- newsmagazine covers -- the whole bit. "Nova" shows him posing with his team, all of whom are wearing T-shirts emblazoned with the words "LAK PAC" and a picture of the then-ubiquitous Pac-Man mouth.

Subsequent experiments at other centers, including New England, dampened the initial euphoria. The treatment was successful in only about a quarter of the patients, and its toxicity was enormous -- potentially fatal if patients were not chosen with exacting care.

"Nova" shows Rosenberg describing himself as "shocked by the vehemence of the criticisms raised," but it also shows three patients at the New England center as they go through the rigors and often anguish of the program.

One of Rosenberg's initial patients, Kathy Donahue, a woman in her late twenties who entered his program with a late stage, untreatable lymph cancer, has a few sharp words for the IL-2 critics. Now "virtually" free of tumors, virtually cured, she says, "I get really upset when I hear criticism of the treatment . . . Doctors have been critical of it, in terms of its being too toxic and that it's not worth putting the patients through. It has been worth it for me. And I feel as though it's my life they're talking about. They're saying to me that my life isn't worth going through some tough times to save. And that's awfully hard for me to listen to because I've been working for a long time to stay alive."

The signal success with Kathy Donahue and a few dozen others is contrasted in the program with three patients at the New England center that the program follows through their treatments and, in two of the cases, to their deaths. A third case showed some improvement at first but has now been switched to a different experimental protocol, where she appears to be doing well.

The treatment is toxic. We are spared very little as we see vigorous, healthy-looking people turned before our eyes into shaking, shivering, nauseated, bundles of misery. Still, the minority successes have been impressive in the cases of some malignant melanomas -- cancerous moles -- after they have spread, and in kidney cancers. The researchers are wrestling now with lowered toxicity and increased potency. The successes, although few, have been dramatic.

The real power of this "Nova" is its insights into the people suffering from cancers that may not be reversible. As one patient put it, "About three days before I come in for another check-up, I start feeling nervous and angry and scared. The tension is incredible. I feel like I'm on a roller coaster, going through these treatments. Going for the results is like going up the hill, and you're going to come down the other side but you don't know if it's going to be the thrill when your stomach turns over or if you're going to throw up. Between treatments I feel like a million dollars, like I'm going to live forever . . . And then I come in and I don't know what I'm going to hear this time."

Dr. David Parkinson, then director of the New England program, is keenly aware of the seemingly conflicting aspects of a study like this one. He says, "I hope that people get an understanding of what it is like to have cancer, to have a disease for which there really isn't very good treatment, how for every victory, there are so many defeats. The reason we go through the agonies is to end these kinds of diseases. People shouldn't have to suffer like this and if we can help then the whole process is worthwhile." ::

Next Tuesday's episode on breast cancer is more superficial and less successful than tonight's powerful look into the interleukin experiment.

Although NBC's Jane Pauley, narrator for both hours, makes a great point that "the tide is turning" on breast cancer -- the episode is titled "Breast Cancer, Turning the Tide" -- that sounds more encouraging than it is. There have been advances in diagnosis and some extension in disease-free periods. But the latest NCI figures on breast cancer indicate that its incidence and its mortality have increased -- incidence by about 1.5 percent a year and mortality, among white women younger than age 50, by 5 percent in the 1984-85 period.

Nova also fails to mention several of the factors involved in this turning tide -- or at least in the efforts to turn the tide.

The program relies heavily on a promising albeit unproven dietary approach to preventing breast cancer, and its producers were clearly forced to backpedal when a planned nationwide study of women on low-fat diets was scrapped by the National Cancer Advisory Board as too expensive and too hard to verify. Still, the program fails to mention hormonal therapy, such as that with the anti-estrogen agent Tamoxifen, which has been deemed the treatment of choice for post-menopausal women whose underarm lymph nodes are free of cancer cells.

Nor does this "Nova" discuss tests that can predict how fast the cancer cells are dividing or even the all-important tests of hormone receptors, which tell how far the original breast cell has been changed by the cancer from its normal state.

The program does point out that breast cancers found by new low-dose mammography are most likely curable and that waiting to find a lump may be waiting too long. That reminder cannot be made too often.