A study of normal and low-salt diets fed 476 Dutch infants has yielded what the American Medical Association yesterday called "the first experimental evidence" that a lower salt diet lowers blood pressure.

More doctors and medical groups have been advising Americans to consume less salt on the assumption that excess salt often, if unpredictably, raises blood pressure and leads to strokes and heart attacks.

But other doctors and some food processors argue that most, though not all, persons can consume safely all the salt they want.

And there has been a lack of scientifically valid studies showing a cause-and-effect relationship between excess salt consumption and high blood pressure.

An article in this week's Journal of the American Medical Association tells how doctors at Erasmus University Medical School in Rotterdam had parents feed 245 babies a normal sodium diet for their first six months of life, and other parents feed 231 babies formulas and solid foods with two to three times less salt.

After six months, the second group had blood pressures 1.8 percent lower, on average, than the normal-diet babies.

Even so modest a difference "may contribute considerably to the prevention of cardiovascular disease" if maintained, according to Rotterdam Drs. Albert Hofman, Alice Hazebroek and Hans Valkenburg.

Their view is backed by an editorial in the AMA Journal by Dr. Julie Ingelfinger of Harvard Medical School.

She said no one knows whether children whose blood pressure is lowered by a low-salt diet will have lower blood pressures in later life. But "information from Mother Nature would suggest that low-salt intake makes sense," she wrote.

"I'm one of those who feel heavy salting of food is not beneficial," she added in an interview. "The amount of salt the average American eats is often 10 to 15 times the necessary intake."

A differing view is taken in an editorial by Dr. Belding Scribner of the University of Washington. He cited another study in the AMA Journal saying that lower salt intake probably has no significant effect on most people.

"Seventy to 80 percent of us . . . do not have to worry about salt intake," Scribner wrote. He advocated salt restriction for four susceptible groups: anyone over 50, all black males, because 50 percent develop high blood pressure, anyone with a hypertensive parent and chronic kidney disease patients.

Health authorities who advocate less salt for everyone say susceptibility to high blood pressure cannot be determined until the condition develops.

Then it is a silent disease until it causes dangerous effects.

Taking the advice of many scientists, the Agriculture and Health, Education and Welfare departments in 1980 issued a set of "Dietary Guidelines for Americans" that flatly advised "Avoid Too Much Sodium."

The Agriculture Department has ordered those guidelines restudied to include "appropriate" changes.

But Food and Drug Administration Commissioner Arthur Hull Hayes Jr. has urged the public to be "as conscious of sodium intake" as of calories, and the FDA is urging food processors to indicate sodium content on food labels.