WASHINGTON (AP) _ Any woman who might become pregnant should either eat specially fortified foods or take a vitamin supplement of folic acid every day to protect against birth defects, a panel of experts said today.

Also, all Americans over age 50 should eat a bowl of fortified cereal every day or take a supplement of Vitamin B12, a nutrient important for making blood cells but one that declines with age, said the Institute of Medicine report.

The new recommendations mean ``in a country where the top two vegetables are french fries and iceberg lettuce, ... people need to make better food choices,'' said Chris Rosenbloom, a Georgia State University nutrition professor representing the American Dietetic Association.

But the review of complex B vitamins _ including folic acid, B12, B6, thiamin, riboflavin and niacin _ cautions against popping huge doses. There's not enough evidence that large amounts protect against heart disease or cancer to urge that Americans eat more, the experts said, and they recommended setting the first ``maximum doses'' for four nutrients to protect against side effects.

The Institute of Medicine, a private organization that advises the federal government, is reviewing the nation's Recommended Daily Allowances, or RDAs, for nutrients.

Today, it announced good news: Most Americans already get plenty of the B family of vitamins, because many have long been added to fortified cereals, breads and grains, staples of the U.S. diet.

The major exception was folate, a trace nutrient whose synthetic form is called folic acid. Folate is found in such foods as spinach, beans and orange juice, but the typical diet didn't give some women enough to protect against certain brain and spinal birth defects that afflict about 2,500 babies a year.

So doctors have recommended that all women of childbearing age consume 400 micrograms of folic acid _ the pill form _ a day. Folic acid provides about twice as much of the nutrient as folate does.

But in January, all fortified foods _ cereals, breads, grains and pastas _ began carrying extra amounts of synthetic folic acid.

The institute report concludes women can get enough protection if they eat these fortified foods on top of a diet rich in folate-ridden foods _ but they must choose either the new foods, a folic acid supplement or both to be safe.

To eat folate, try one-half cup of spinach, with 130 micrograms; one-half cup of boiled navy beans, 125; one medium orange, 45; or one ounce of dried peanuts, 30. For extra folic acid, some cereal brands provide 400 micrograms in a single bowl, or get that amount from a sandwich, pasta and two other servings of fortified grains.

Up to 30 percent of people over age 50 have lost the ability to absorb adequate vitamin B12 from meat or dairy products, the report found. People need only 2.4 micrograms a day _ the amount in a mere three ounces of beef _ but the institute recommended that older Americans eat fortified cereal or grains or take a daily vitamin supplement to absorb enough.

People are flocking to folic acid and vitamin B6 supplements because of reports that they might protect against heart disease or cancer. That research ``is promising,'' the experts said, but not conclusive _ so they did not recommend large increases.

But to avoid side effects, the report recommended daily upper limits on some nutrients:

_No more than 100 milligrams of Vitamin B6. Higher doses could cause painful nerve disorders.

_No more than 1,000 micrograms _ or 1 milligram _ of folic acid. People who are deficient in Vitamin B12 can suffer crippling neurologic damage if they take high doses of folic acid. Yet in an ironic turn, folic acid consumption can hide early symptoms of Vitamin B12 deficiency.

_No more than 35 milligrams of niacin, a little over twice the daily recommended dose. The higher doses cause blood vessels to dilate, resulting in burning, tingling and a red rash. Supplements containing up to 400 milligrams are sold without a prescription.

_No more than 3.5 grams a day of choline, a related nutrient important for maintaining cell membranes. Higher doses can cause low blood pressure, sweating and a fishy body odor.