Sen. Orrin G. Hatch (R-Utah), chairman of the Labor and Human Resources Committee, said yesterday that Congress should consider changing key elements of the food safety laws that have governed the production of the nation's food supply for 25 years.

"I personally believe we are going to have to come up with some legislation" to incorporate new scientific judgments on what consitutes "safe" food and food additives and how those decisions are made, Hatch said at the close of three days of hearings on the issue.

Several Reagan administration officials from the Departments of Agriculture and Health and Human Services who testified yesterday agreed with concerns expressed earlier this week by two former Carter administration food and drug commissioners that parts of the law were too inflexible.

The hearings raised several questions including:

Whether the current definition of "safe" should be modified to change the current standard--"reasonable certainty of no harm"--to a standard that a food or food additive poses an "insignificant risk."

Whether the Delaney amendment, a 1958 law prohibiting the addition of substances that cause cancer in animals or humans to the food supply, should be modified in light of improved scientific detection methods that can identify infinitesimal amounts of carcinogens.

Whether food safety laws should incorporate a standard balancing the risks of a substance against its quantifiable benefits.

While emphasizing that the Reagan administration does not intend to submit food safety legislation, Assistant Agriculture Secretary C.W. McMillan said yesterday that "the law should be sufficiently flexible to deal with substances that may be questionable, but which may nevertheless provide important health benefits to consumers."

Consumer advocates argued, however, that food safety laws ought to be strengthened, not relaxed.

They also vigorously opposed any changes that would permit cancer-causing substances to be added to foods, even in trace amounts, and challenged Hatch to produce an example of a food additive whose prohibition had harmed the public.

Earlier this week, former Food and Drug Administration commissioner Jere E. Goyan said "an intelligent approach" to carcinogens would be for Congress to quantify what it believes to be an appropriate risk of cancer.

He cited as an example the FDA's attempt to define as safe animal food additives that could result in one additional cancer death per million people over a lifetime.