Congress, without fanfare, has approved one of the most substantial revisions of law governing the regulation of food, drugs and medical devices in the nation's history. The changes promise a vastly expanded range of authority for the Food and Drug Administration.

In four separate bills, Congress approved the first comprehensive set of food-labeling guidelines in 17 years, expanded the power of federal regulators to monitor the safety of medical devices, amended the Orphan Drug Act and authorized $100 million for a new FDA headquarters.

But with the expanded authority comes the task of absorbing and interpreting new responsibilities that are almost certain to place a tremendous short-term burden on the FDA, occupying key parts of the agency for years to come and forcing a reorientation of the FDA's regulatory strategy.

"There's never, never been anything {in the FDA's history} to compare to this," said Covington & Burling attorney Peter Barton Hutt, a former FDA chief counsel. "There is more here for the FDA to assimilate than has been passed by Congress before in even any five-year period."

The FDA's new responsibilities fall into three areas. First, the rules for so-called orphan drugs have been changed. The law, which grants monopoly status to drugs for rare diseases as a way of encouraging development of such drugs, provides for two extra regulations that permit competition once diseases -- such as AIDS -- are no longer considered rare.

In the medical devices area, Congress's rewrite of existing law was more extensive. Under the current system, hospitals and health-care providers report deaths and injuries from medical devices to the manufacturer, which is then responsible for telling the FDA. This system, however, has been criticized as haphazard and ineffective in identifying flawed devices.

In its place, Congress has mandated the direct reporting of problems to the agency. The FDA also has been charged with developing a tracking procedure to speed recalls, and has been given a broad class of new powers to issue civil penalties of up to $1 million for violations of the law.

The centerpiece of the FDA-related legislation, however, is the Nutritional Labeling and Education Act, Congress's answer to what Health and Human Services Secretary Louis W. Sullivan earlier this year called the "tower of Babel" in U.S. supermarkets. Sullivan proposed a set of food-labeling rules last spring, but the congressional action expands and clarifies the administration proposals.

In the area of health claims, for example, food manufacturers had been taking what many nutritional experts considered to be extraordinary liberties in claiming that ingredients in their products helped prevent disease. The legislation stipulates that scientific data supports only four such claims: that foods low in salt may help prevent high blood pressure, that foods high in calcium help prevent osteoporosis, and that reducing fat and increasing fiber may reduce the risk of cardiovascular disease and cancer.

Any other claim must be pre-approved by the FDA and must be supported by broad agreement among scientific experts.

On content claims -- such as whether and when a food can be called "light" or "high in fiber" or "low-calorie" -- the legislation establishes a definitive list of how and when terms can be used and requires specific government approval for the use of some wording.

According to the measure, food labels must present nutritional information in the same way and meet standards. Total fat per serving, for example, must be included, along with additional breakdowns of unsaturated fat and saturated fat.

"This bill is a win-win for consumers and the food industry," said C. Manly Molpus, president of the Grocery Manufacturers Association. "More information about food products under a single, national uniform system will benefit both shoppers and manufacturers."

In the long run, food and drug law experts agree, the new rules will make the FDA's job easier.

For example, the measure allows states, for the first time, to enforce federal food-labeling law, which some experts said should eventually ease the burden of the agency's compliance staff.

More important, the imposition of a single, uniform standard for health claims should make enforcing federal law much easier for the FDA.

Under the old rules, the agency responded to individual instances of questionable health claims one at a time, after the fact. If, for example, a cereal manufacturer wanted to say that its product lowered cholesterol, it would state that claim on the box, start selling the cereal in supermarkets, and then wait to see whether the agency would respond.

Given that health claims have sprouted on thousands of food products over the past few years, deciding which labels were acceptable and which ones were not, and then beginning lengthy legal proceedings against the objectionable labels, proved to be more work than the agency could handle.

The promise of the new rules is that the agency will no longer have to go after offending companies one by one. There are now clear guidelines about what can and cannot be said on a label, and any attempt to deviate from the guidelines now requires prior agency approval. Some food law experts, however, say that this type of prior restraint on marketing claims has the potential to raise constitutional questions. But there is no question that it will make the FDA's task easier.

"Although the nutrition bill entails certain front-end costs on the part of the FDA, in the end it will save resources as the agency moves from individual enforcement actions to standards that will apply federal law across the nation," said Rep. Henry A. Waxman (D-Calif.), one of the architects of the legislation.

Getting to that point, however, may not be easy. All of the food-labeling guidelines issued by the agency last spring will have to be withdrawn and redrafted. Regulations will have to be drawn up interpreting the law's requests, and staff deployed to match the new responsibilities. In his written responses to congressional questions, new FDA Commissioner David Kessler said one of his first tasks will be to determine whether the agency's resources match its new responsibilities.

"It's awfully easy on the outside to say that we'll just sit down and write the regulations," said Hutt, the former FDA counsel. "But the statute invariably does not address important issues, so the agency has to figure out what is meant. Sometimes the statute has impractical requirements. . . . For the next little while, everything else will have to be set aside."