Federal regulators should look more closely at the potential health effects of some genetically modified plants before they can be grown as commercial crops, a scientific advisory panel said yesterday.

It also said regulators should check for potential food safety problems after people eat the products.

The report by a committee of the National Research Council and Institute of Medicine said regulators should target tighter scrutiny at genetically engineered varieties that have greater levels of biological differences from current plants.

Some chemicals in plants can create allergic reactions or otherwise make some people sick. To prevent such problems, the study recommended a case-by-case approach to the applications based on compounds in conventional as well as biotech plants, rather than the current focus on biotech varieties.

The report also said the government should develop better ways to determine whether genetically modified foods cause health problems. Among these could be systems to trace foods with greatly altered levels of those compounds through the food supply and to check populations to see whether there are health problems among people who eat the foods.

The primary focus, however, should be on the approval process, "and we would hope that, for the most part, there wouldn't be a great deal of post-market tracking," said the committee chairwoman, Bettie Sue Masters, a professor of chemistry at the University of Texas Health Science Center in San Antonio.

The report said that genetic engineering of food crops, although relatively new, appears to be a safe technology and that there is no evidence it has harmed health. Committee members emphasized that current biotech crops have gone through extensive safety checks.

"What we are talking about is from this point going forward," said Dean DellaPenna, a professor of biochemistry and molecular biology at Michigan State University.

The report was done for the Food and Drug Administration, the Agriculture Department and the Environmental Protection Agency, which oversee biotech crop applications.

Michael Phillips, vice president of agricultural science and regulatory policy at the Biotechnology Industry Organization, a biotech trade group, said the report should "lay to rest the few naysayers who continue to question the safety of these crops."

Consumer advocates said the report also supported their positions. "The report clearly and correctly states that biotech foods could have unintended consequences," said Gregory Jaffe, biotechnology project director of the Center for Science in the Public Interest.

The National Research Council and the Institute of Medicine are arms of the National Academy of Sciences, a private, congressionally chartered organization that advises the government on scientific and technical matters.