Each morning, in Lou DeMouy's Silver Spring home, there is a small but unchanging ritual that provides him with a large measure of comfort and a little bit of a kick before he heads downtown to his job as a government economist.

That ritual, of course, is built around the coffee that DeMouy drinks.

"It gives me a lift, and I like the taste," he said as he waited for the clerk at the coffee specialty store to grind and bag the Colombian blend that he had just purchased for $3.95 a pound.

DeMouy -- like millions of other Americans -- continues his morning coffee ritual, day in and day out. Yet an increasing number of reports by government and other researchers are raising new questions about the safety or health effects of caffeine. The studies have linked caffeine to a wide range of disorders from insomnia and nervousness to heart disease and birth defects.

The findings have not been sufficiently conclusive for scientists to condemn caffeine outright. But enough evidence has been compiled that they generally aren't willing to give caffeine a completely clean bill of health, either.

"We don't know if caffeine is safe or unsafe," said Dr. Sanford Miller, director of the U.S. Food and Drug Administration's bureau of foods."But the questions are there, and my recommendation would be that if you are in a susceptible group -- a pregnant woman or a young child still undergoing brain development -- you should limit your intake of caffeine. It is the prudent thing to do."

"Why take a chance?" he concluded.

Here is the essence of the concern:

Pregnant women are advised to avoid caffeine because tests show it can pass from their bloodstream through the placenta to the fetus. Caffeine also has been detected in the milk of mothers who breast feed. Although there is no proof that caffeine can cause a birth defect in humans, the FDA has found that high doses of caffeine force-fed to pregnant rats caused birth defects in the rats' offspring. Defects included cleft palates, deformed faces and partly or completely missing digits -- the equivalent of missing fingers or toes in humans.

Young children up to about 8 years of age whose brains still are developing should have only limited amounts of caffeine, which they typically get from soft drinks.

"The concern is that caffeine might impair the development of the brain or central nervous system," an FDA spokesman said.

Adults who consume excessive amounts of caffine -- usually more than one gram of caffeine a day, the equivalent of 10 cups of coffee -- have been found to suffer from "caffeinism," a syndrome characterized by nervousness, irritability, agitation, headaches and muscle twitching. When a heavy caffine user suddenly reduces his consumption, perhaps by drinking less coffee or cola, the person often develops severe headaches.

Does that mean coffee drinkers should abstain?

"I drink coffee and I will continue to drink it -- but I'm not in a susceptible group," the FDA's Miller said. He and other experts generally agree that, except in the case of pregnant women and young children, moderate consumption of coffee and other sources of caffeine by the average adult hasn't been shown to cause harm.

But what is moderate for one person may be excessive for someone else.

Lee Johnson, a 29-year-old Washington writer wearing sunshades and one small gold hoop earring, said that he limits himself to one cup of coffee a day, explaining: "If I drink two or three cups, I really feel it . . . so I have just one cup."

But Muriel Anderson, a cheery blonde of 64 wrapped in a tiger-stripe coat, said she drinks as many as seven cups a day (some of them only partly filled) without side effects.

"I make three or four pots of coffee a day, and always one at 10 p.m. just before my husband gets home from work," she said.

America's passion for coffee -- the main source of caffeine in the U.S. diet -- dates to the American Revolution, when unhappy colonists sought a substitute for tea, which had become politically symbolic and unpopular at about the time that some of them dumped it into the harbor during the Boston Tea Party.

Originally discovered in Ethiopia, coffee is grown today mostly in Latin America.Through the years it has become the cornerstone for the typical American meal. An estimated 56.6 percent of the U.S. population over age 10 now drinks coffee.

In a report earlier this month, Harvard University scientists said that they had found a link between coffee drinking and cancer of the pancreas. But the scientists said they think something in coffee other than caffeine may be the cause, although caffeine was not ruled out. The Harvard group also acknowledged that the association between coffee and cancer of the pancreas isn't yet proved, and that more studies are needed.

In its pure state, caffeine is a white powder that has been described as a mass of glistening, white needles. It occurs naturally in an estimated 63 plant species that include, besides the coffee bean, the leaves of tea, the cocoa bean and the kola nut.

A drug that acts on the central nervous system, caffeine constricts the blood vessels, speeds up the heart and stimulates the brain, stomach, gut, kidneys and gonads. It has the effect of an amphetamine on some people who consume large amounts of caffeine, pepping them up at least temporarily and leaving them with withdrawal pains if they suddenly reduce their caffeine intake.

Coffee, tea and cola drinkers generally are aware that those beverages contain caffeine: 75 to 155 milligrams in one five-ounce cup of coffee, 28 to 44 milligrams in one five-ounce cup of brewed tea, and 32 to 65 milligrams per 12-ounce can of cola or "pepper" drink.

But besides those three basic sources of caffeine, there is a variety of foods and products from which consumers regularly and routinely receive a dose of caffeine. They get it when they sip cocoa, munch a candy bar or take a stay-awake pill, a diuretic or a headache tablet other than aspirin. The amount of caffeine ranges from a modest 5 milligrams for a cup of cocoa to a hefty 200 milligrams for a Vivarin alert tablet.

Consumers also get trace amounts of caffine when it is added -- generally in the form of a coffee flavoring -- to baked goods, frozen dairy products, soft candies, gelatins and puddings.

The Food and Drug Administration estimatee that 2 million pounds of caffeine is added to foods in the United States each year. Most of this goes into soft drinks, in accordance with traditional corporate recipes for cola and "pepper" beverages and in compliance with government rules intended to standardize those products.

The basis for the federal regulation goes back nearly a century to Atlanta Druggist John S. Pemberton. Working over a three-legged pot in his backyard, Pemberton produced a cola drink from a kola nut extract and an added pinch of caffeine. The extra pinch supplemented the caffeine naturally present in the kola nut and helped give Pemberton's cola drink its distinctive taste.

Pemberton later sold the rights to the drink to The Coca-Cola Co.

Still later, federal regulators sought to impose a standard for soda water contents and labeling, and decided to require the extra pinch of caffeine in any drink bearing the cola or "pepper" name on the label. The maximum amount of caffeine in such drinks is .02 percent of the total weight of the product. If no caffeine is added, the company must use a name other than cola or "pepper."

Now, because of growing questions about caffeine, the FDA wants to change its rule to eliminate the requirement that caffeine be added and allow the marketing of decaffeinated cola and "pepper" drinks.

Soft drink manufacturers, however, oppose the proposed rule change.

"There's no reason to do that," said Jay Smith, a representative of the National Soft Drink Association. "Only a maximum amount of caffeine is specified in the rule, so a manufacturer could add just a minute amount and be in compliance."

Manufacturers aren't expected to reduce the caffeine they add, however, because of the effect it might have on the taste. The general position of the coffee and cola industry is that nothing about the potential dangers of caffeine has been proven.

Consumer groups, in the meantime, have been pushing the FDA to take a harder line on the caffeine issue. The Center for Science in the Public Interest, a Washington-based organization directed by Dr. Michael Jacobson, has asked the FDA to require that caffeine products be labeled with warnings about possible birth defects.

But the agency, which has been without a permanent head since Commissioner Jere E. Goyan resigned in January, has taken a wait-and-see attitude. Among other things, officials are awaiting the results lof a second set of FDA tests that are underway on caffeine's effects on pregnant rats. They also are wrestling with executive orders issued by President Reagan, which require that the cost to industry of major new regulatory proposals be determined prior to enactment. And they are wondering about the size of their budget to finance further activities.

"We are trying to get the word around . . . that it is prudent to reduce your caffeine consumption if you are pregnant," said Bill Grigg, an FDA public information officer. "We had a press announcement when the first study was done last fall, and we have distributed some fliers on caffeine and pregnancy through supermarkets in some parts of the country.

"But we don't know if we will have enough money to keep distributing that flyer."