''The problem is not so much whether we have too much salt in our diet as it is the deterioration of the American diet,'' said Dr. David McCarron, a professor of medicine at Oregon Health Sciences University in Portland, who argues that salt makes little difference in blood pressure control when people eat balanced diets that emphasize fruits, vegetables and low-fat dairy products. ''That's really the issue.''

Dr. Michael Alderman, a professor of medicine and epidemiology at Albert Einstein College of Medicine in the Bronx and past president of the American Society of Hypertension, said: ''I don't believe there is any basis whatsoever for a public health recommendation for eating any particular sodium content diet. A scientific problem ought to be solved by data. And there is no data.''

Actually, there are mountains of data on the relationship between salt and blood pressure, but most is so difficult to interpret that it is not at all uncommon for the same study to be cited in support of both pro-salt and anti-salt positions.

People need at least some salt -- no one argues with that. But the minimum amount a person needs to survive and maintain a normal blood pressure is thought to be around 400 milligrams of sodium per day, far less than the 3,500 milligrams per day in the average American diet. (Sodium units are generally used by convention in scientific discussions of salt intake, since only salt appears to influence blood pressure, while other sources of sodium, like bicarbonate of soda, do not.)

An Effect, But How Big?

Salt affects blood pressure -- no one argues with that, either. After all, blood is simply a lot of cells floating around in a salt water solution. Eat a few extra tablespoons of salt and a cascade of water-retaining hormones dilute the extra salt in your blood back to the right concentration, raising blood volume and blood pressure a little until the extra salt is eliminated by the kidneys.

Cut back on salt, and you will probably be less thirsty, drink less water and your blood volume and pressure will fall a little. Another set of salt-retaining hormones are then activated to make the kidneys retain all the salt, and things return to normal.

Normal blood pressure is considered around 120 over 80 millimeters of mercury. The first number, or systolic, represents the pressure in the bloodstream during a heartbeat, and the second number, or diastolic, represents the pressure after a heartbeat.