IT'S often hard enough just to get a job. But now some personnel departments are confronting applicants with unusual requirements for employment.If, for instance, you smoke or are overweight, you may run into companies that will reject your application, regardless of your qualifications. In North Miami, Fla., an applicant for a municipal clerk-typist job found her interview concluded when she was unable to sign an affidavit declaring she had not smoked cigarettes or used any tobacco products for 12 months. She filed suit. Four paramedics in the Los Angeles fire department, disciplined for failing to lose two pounds a month, have brought suit against the city, charging that they are being discriminated against because of their weight. For a brief period, applicants for municipal jobs in Athens, Ga., had to pass a cholesterol test. If you are a mountain climber, a sky diver, or a motorcyclist, you may not be hired unless you give up your high-risk recreation. As one example, a small property-development company in Atlanta prohibits employees from taking part in these activities. Elsewhere, some are being kept from new jobs, while others are required to pay surcharges on their company health insurance. The common issue for employers, of course, is the rising cost of health insurance. But the insistence of employers upon rules that control the behavior of employees outside the workplace opens up chilling possibilities. In a future driven by health-insurance costs, could qualified applicants lose out on jobs because their medical record showed their parents had diseases classified as hereditary? It is an extreme scenario. But once an employee's experience and competence can be disregarded because of after-hours activities that disturb actuarial accountants, the chances for injustice proliferate. In the end, this newest form of discrimination could lead to a preference for well-oiled robots over creative but unpredictable human beings.