NOBODY expects employers to provide groceries, housing or clothing, but for odd historical reasons American employers have evolved into providers of health insurance. Nearly two-thirds of Americans under 65 rely on health coverage from an employer.

Some of America's largest companies, maybe eager to level the playing field, favor requiring employers to provide insurance. But they have it backward. They should be advocating an end to employer-financed health coverage altogether.

Why should we hate the employer-financed system? Let us count the ways:

It makes it difficult or sometimes even impossible for people to change jobs, not only damping economic efficiency but reducing the competition for labor and, therefore, reducing wages. Without alternative health coverage, there is ''strong evidence for job lock,'' wrote two economists, Jonathan Gruber and Brigitte C. Madrian, in a National Bureau of Economic Research study released this year.

It suppresses the creation of new businesses because, for many potential entrepreneurs, quitting a job means forgoing health insurance, a risk too big to take.