AS a sort of reality check, Dr. J. William Langston, director of the Parkinson's Foundation in Sunnyvale, Calif., periodically asks fellow scientists whether they would rather make a great discovery or win a Nobel prize. Most, he said, have to stop and think.

That should come as no surprise. The Nobel looms like a coronation -- a personal and professional validation (to say nothing of the prize money itself, usually $1 million or more, and the potential for future financial gain). Symptoms of Nobelitis have been spotted even among fledgling scientists still in school.

Some scientists devote whole careers to lobbying for the prize and some may be more adept at lobbying than they are at science. (The same criticism can be raised about journalism's Pulitzer Prize, but that's another story.)

''It's the same kind of motivation that sends people to Hollywood when they have no talent,'' said Dr. Ponzy Lu, a biochemist at the University of Pennsylvania.

Lobbying tactics have ranged from the relatively tame -- getting to know members of the Nobel committee and asking friends to promote your work to them -- to the aggressive. Some would-be Nobelists are said to have promoted a hypothesis by giving it a catchy name and by panning competitors' papers when reviewing them for scientific journals.

The myth is that the Nobel is supposed to recognize the very best of science. The reality is that ''it has become part of science itself,'' Dr. Langston said. The quest for a Nobel starts to drive science, he said, and when a scientist wins the prize, the Nobel validates the research. Soon, Dr. Langston said, ''it isn't clear what's driving what anymore.''

Dr. Lee Silver, a molecular biologist at Princeton University, said: ''It's a very peculiar psychological thing that goes on. If you're a good scientist, you should always be doing experiments to attempt to discredit your own theory. But you have this psychological block -- you don't want there to be an experiment that disagrees.''

''The Nobel prize certainly gets in the way of doing that,'' Dr. Silver said. Which is why, Dr. Langston said, researchers trying to avoid being seduced by their own theories often tell themselves, ''It's O.K. to sleep with a hypothesis, but you should never become married to one.''

Why Bother?

Even if a Nobel prize is given for work that was wrong, the winner is still a Nobel laureate. In 1959, Dr. Arthur Kornberg won for discovering the enzyme that copies DNA, the genetic material. It turned out years later that he had discovered the wrong enzyme. The award to Dr. Kornberg not only overshadowed the scientists, including his son, Thomas, who eventually discovered the correct enzyme in 1970, but may have impeded that very discovery.

Dr. Lu says scientists thought to themselves: ''Here's this guy. He's the greatest enzymologist in world and he got a Nobel prize for working on this system. Why compete with him?''

Now, some scientists are raising similar questions about the award last week.

Dr. Stanley Prusiner of the University of California in San Francisco won the Nobel in Physiology or Medicine for his hypothesis that certain rare neurological diseases are caused by rogue proteins, which he has named prions. It is a heretical idea because proteins have no genetic material and so cannot reproduce like viruses or bacteria. Dr. Prusiner suggested that, instead, a protein folds itself into an unusual shape. It then touches other proteins that are folded normally and, in a sort of slow-motion chain reaction, induces them to change their shapes, too. The accumulation of aberrant proteins in the brain cause diseases like mad cow disease, scrapie insheep and Creutzfeldt-Jakob disease in humans.

His supporters say his work is brilliant. His detractors say all of his evidence is consistent with the notion that the diseases are caused by conventional agents, like viruses. Prions, said Dr. Robert G. Rohwer, director of the molecular neurovirology unit at the Veterans Affairs Medical Center in Baltimore, are ''the cold fusion of infectious diseases.''

Dr. Prusiner says he feels vindicated. Some scientists say that's too bad.

''My fear is that debate is going to be stifled,'' said Dr. Laura Manuelidis of Yale University School of Medicine. ''That's the problem with Nobel prizes. If people feel everything is decided, you can't possibly risk going against the grain.''

Dr. Ashley Haase of the University of Minnesota predicts the award will have the opposite effect, stimulating scientists to enter the field and really try to understand the nature of brain diseases.

Of course, even if someone discovers a virus that causes the diseases, it is unlikely that another Nobel prize will be bestowed for work in the same field. Dr. Prusiner's prize was the second in the field -- in 1976, Dr. Carleton Gajdusek of the National Institutes of Health got one for showing that the diseases are transmissible, postulating what he called a ''slow virus.''

The real question is whether, without the prospect of a Nobel, scientists would be less eager to challenge a prize-winning hypothesis and pursue the truth themselves.

Photo: The Nobel Prize (Associated Press)