Sad people are nice. Angry people are nasty. And, oddly enough, happy people tend to be nasty, too.

Such (allowing for a little journalistic caricature) were the findings reported in last month's issue of Psychological Science. Researchers found that angry people are more likely to make negative evaluations when judging members of other social groups. That, perhaps, will not come as a great surprise. But the same seems to be true of happy people, the researchers noted. The happier your mood, the more liable you are to make bigoted judgments -- like deciding that someone is guilty of a crime simply because he's a member of a minority group. Why? Nobody's sure. One interesting hypothesis, though, is that happy people have an ''everything is fine'' attitude that reduces the motivation for analytical thought. So they fall back on stereotypes -- including malicious ones.

The news that a little evil lurks inside happiness is disquieting. After all, we live in a nation whose founding document holds the pursuit of happiness to be a God-given right. True to that principle, the United States consistently ranks near the top in international surveys of happiness. In a 1994 survey of 41 countries, only the supposedly dour Swedes surpassed us in ''positive affect.'' (Elaborate scales have been invented to measure individual happiness, but researchers admit that difficulties remain; for example, a person is more likely to express satisfaction with his life on a sunny day than on a cloudy one.) Of course, happiness has always had its skeptics. Thinkers like Aleksandr Solzhenitsyn have criticized it as a shallow and selfish goal. But the discovery that happiness is linked to prejudice suggests a different kind of case against it. Does happiness, whether desirable or not in itself, lead to undesirable consequences? In other words, could it be bad for you, and for society?

The burgeoning new science of happiness hasn't paid a lot of attention to this question. Its practitioners are more concerned with the causes of happiness than with its effects. Defining happiness as ''well-feeling'' -- being satisfied with life, having episodes of joy -- they have discovered some interesting things: a large part of happiness seems to be genetic; marriage fosters it, but having children doesn't; men become happier with age, women less happy; money does little to boost happiness; religious people are happier, possibly because of the social support they get from church; and so forth.

As to the consequences of being happy, they are widely presumed to be positive. Happiness is held to lengthen life, buffer stress and make people more productive on the job. Some of these notions appear to be justified. A Dutch study in the 1980's, for example, found that a happy 70-year-old man can expect to live 20 months longer than his less happy counterpart. But an earlier American study found that children who are cheerful and optimistic end up having shorter life spans (perhaps because they take more risky chances).