The Agriculture Department will issue tighter rules this morning to keep pharmaceuticals grown in plants out of the food supply, promising a greatly stepped-up inspection regimen to be sure people don't wind up eating someone else's drugs in their breakfast cereal.

The new plans include greater buffer zones between ordinary crops and drug-containing crops, better training for farmers and employees of biotechnology companies, stricter harvesting requirements, and a sevenfold increase in the number of inspections to which the biotech companies will be subjected every year.

Ann M. Veneman, the secretary of agriculture, pledged "stringent" oversight of this nascent sector of the biotech industry, declaring: "It's very important that we regulate in a way that allows this technology to proceed so we can reap the benefits of it."

However, the new rules were immediately criticized by the food industry, consumer advocates and environmentalists. People from all three groups said the rules, though a step in the right direction, don't go far enough to ensure that crops containing pharmaceutical or industrial compounds don't spill over into food, as nearly happened last fall in Iowa and Nebraska.

In particular, these groups faulted the Agriculture Department for not restricting the locales where such crops can be grown or requiring that they be grown only in plants not usually eaten.

Some skeptics said the department had caved in to pressure from the biotech industry and to political interests in the Midwestern corn belt that want to see that region grab a piece of the new industry.

"They put a Band-Aid on an old, antiquated regulatory system, and sooner or later that Band-Aid is going to fall off," said Matt Rand, biotechnology campaign manager at the National Environmental Trust in Washington. "There will be a mistake, and we're going to see contamination of the food supply."

The debate involves one of the strangest, and potentially most significant, applications of the new biology sweeping through the nation's laboratories.

Into scores of plants, biotech companies have inserted new genes that encode instructions for making pharmaceutical or industrial proteins. Their plan is to grow fields of these plants, harvest them, refine the proteins and package them like any other drug or chemical. It is a cheaper way and, in some cases, the only way to grow some of these useful proteins.

The idea has enthused farmers eager for more-valuable crops. And biotechnology companies argue that the technology could cut the cost of producing drugs, making possible such applications as a cancer vaccine custom-designed to attack an individual patient's tumor.

As it happens, though, the companies have achieved their greatest successes to date in plants also grown as food, and particularly in corn. Corn is the nation's largest crop, and corn pollen containing the foreign genes can spread readily to nearby fields, introducing the genes into food corn that could make its way into such products as cornflakes or baby food.

The risks of the new technology became apparent last year when ProdiGene Inc., a small company in College Station, Tex., mishandled pharmaceutical corn in Iowa and Nebraska. Nearby fields of food corn had to be burned in Pocahontas County, Iowa. In Aurora, Neb., small amounts of corn leaf containing a pig vaccine may have contaminated a vast warehouse of soybeans. The beans were quarantined just before they reached processing centers and were eventually burned.

ProdiGene is in the throes of a management shakeup aimed at tightening procedures, and other biotech companies using the technology are busy reviewing their plans for the coming growing season. So far, the pharmaceutical crops have been grown on no more than a few hundred acres a year, but that could become thousands or even tens of thousands of acres as the companies move toward full commercialization.

It became clear in the ProdiGene case that the government's requirements, meant to keep food crops and pharmaceutical crops strictly separated, were weak in some respects and not fully enforced in others. The Agriculture Department acknowledged last fall that it might need to tighten the rules and step up enforcement. It will do that with new guidelines to be published this morning in the Federal Register.

The new rules, which leaders of the Agriculture Department outlined yesterday, are not a radical overhaul of the old ones at first glance but may hold greater implications than is immediately evident.

The department will, for instance, double the buffer zones that biotech companies have to maintain between their specialty corn and ordinary corn. In some cases the buffer zone will now be a mile instead of a half-mile, a requirement that may rule out large swaths of the Midwestern corn belt, since finding a spot of land there with no corn growing within a mile is no mean feat.

The department will also require that land used to grow pharmaceutical corn lie fallow the next year. If in place last year, this provision would have prevented the ProdiGene soybean problem in Nebraska. In that instance, soybeans were grown on a plot used to grow pharmaceutical corn the previous year, but leftover corn kernels sprouted in the beans and may have contaminated them at harvest time.

Yet farmers are reluctant to take good land out of production for a year, and the potential expense of doing so in the Midwest may well drive companies to consider growing their crops in places such as Arizona or Hawaii, where little food corn is grown.

The new rules will require that pharmaceutical crops be harvested with separate or specially cleaned equipment and stored in dedicated bins, yet another large expense. And, in perhaps the most significant change, the Agriculture Department said it would send inspectors to look at every biotech plot at least seven times over two years, compared with one time under the old rules. Some groups expressed skepticism that the Agriculture Department could round up enough inspectors, but Cindy Smith, acting head of biotech regulation, said she would borrow them from other agencies.

The Agriculture Department ruled out some of the more stringent steps recommended by environmental groups or the food industry, such as geographic restrictions to keep the new crops away from the agricultural heartland. The Agriculture Department has been under intense political pressure, particularly from Sen. Charles E. Grassley (R-Iowa), chairman of the powerful Senate Finance Committee, not to institute rules that would drive the new industry out of the Midwest for good.

The Agriculture Department said it would further tighten regulations later this year, and several groups made clear yesterday that they would continue pressing for more vigorous regulation. For instance, the Grocery Manufacturers of America, a Washington trade group that includes companies making most of the processed foods in American pantries, declared that "much more needs to be done to ensure the safety and purity of the food supply."