There is no evidence that they are not safe to eat or that they are environmentally harmful. So said the prestigious National Academy of Sciences, after a long study of genetically modified crops, the stuff that's damned and banned in Europe as ''Frankenfoods.''

The conclusion must be taken seriously, because it is the work of recognized specialists from a wide span of relevant scientific disciplines and institutions convened in a setting designed to exclude partisan interests.But there's a worrisome message implicit in the favorable findings - namely, that genetically modified (GM) foods entered the food supply in immense quantities while many important questions about their effects on health and the environment were unexamined. And the postscript is that the effects still have not been thoroughly researched.

It's hard to avoid the thought that maybe we were just plain lucky when the biotechnology industry made the transition from small, confined agricultural test plots to shipping genetically modified seeds around the world.

Last year GM seeds were used in more than 70 million acres of plantings in corn, soybeans and other crops in the United States. A majority of processed foods in America now contain genetically modified ingredients; they're virtually impossible to avoid.

The National Academy report focused on just one aspect of genetic modification, the introduction into plants of genes designed to protect them against pests so that the costs and hazards of chemical pesticides could be eliminated.

Navigating between its findings of no harm so far and unanswered questions, the report recommended study of resistance that pests might develop to insecticides produced by genetically modified plants. It also called for further research on the unintentional spread of pest-resistant genes to weeds that are normally attacked by insects.

Further research on the introduction of allergens into crops was recommended, as was research on the human and environmental effects of toxins entering the atmosphere from plants genetically modified to resist pests.

The organizational layout of government regulation for GM crops, established in 1986, was criticized as out of date and lacking clear boundaries for the agencies involved - the Department of Agriculture, the Food and Drug Administration and the Environmental Protection Agency.

The report also opposed EPA's proposal to grant automatic exemptions for certain categories of GM plants, cautioning that in some circumstances health and environmental hazards might ensue.

The report on genes and pesticides comes just as the biotechnology industry, rocked by Frankenfood resistance in Europe and Japan, is organizing another debacle on the wreckage-strewn road to a new era in agricultural productivity.

The surest way to get people to worry about something that they're not worried about is to advise them that there are no grounds for concern. On that basis, we can expect a rising tide of fears about genetically modified foods in the United States, where the public has shown little interest in the subject.

Alarmed by mass resistance abroad, seven major companies have set up a $50 million fund to assure Americans that the stuff is safe to eat. Ads to that effect are already appearing on TV under an appropriately witless slogan: ''Good ideas are growing.''

Though environmentally purist public-interest groups have tried to incite a supermarket rebellion, Americans remain remarkably unconcerned about the genetic make-up of their foodstuffs.

True, in preemptive moves, Gerber and Heinz last year banned genetically engineered corn and soybeans in their baby foods. But the food issue remains short of the big time in the United States, probably because of trust in government monitoring of the food supply and a long tradition of innovation in food products.

In Britain, the center of European resistance to genetically altered food crops, the government's credibility on food-related matters has never recovered from revelations of the neglect of warnings about the spread of so-called mad-cow disease, a fatal human brain disorder originating in infected beef.

Trust in honest government science is the main difference between U.S. acceptance of GM foods and foreign rejection. TV ads are no substitute for trust. Inadequate regulatory oversight may make it easier to get products to market. But one bad step and the GM food industry can pack up.

Advice on this matter can be obtained from the nuclear-power industry - or what's left of it.