Early next spring, two Maryland cornfields may be the sites of a historic experiment. If, as expected, the Environmental Protection Agency and the Department of Agriculture give their blessings, Crop Genetics International Corp., a Hanover, Md., agricultural biotechnology company, plans to take a genetically altered bacterium outside the laboratory and test it as a pesticide against the European corn borer, a caterpillar that causes $400 million worth of damage to American agriculture every year.

In the short history of American biotechnology, there have been only three legally sanctioned outdoor experiments of this kind. The first two -- attempts by California researchers to use bioengineered microbes to inoculate potatoes and strawberries against frost damage -- so alarmed the public that the experiments were mired for years in bitter litigation. Even when they were finally approved last April, vandals sabotaged them.

But the third experimental release went off with little fanfare last month in South Carolina after a carefully orchestrated campaign to garner community support. Crop Genetics hopes to emulate that example with its tests in Beltsville and Queen Anne's County next spring.

The issue of release of manmade life forms has been, over the past few years, the most controversial of all the public questions facing the biotechnology industry.

Unlike traditional chemical pesticides, microorganisms can reproduce themselves, increase in number and spread beyond their point of application. Some environmentalists have argued that without careful monitoring, bioengineered bacteria could upset the ecological balance or even pose a long-term health risk to humans.

Crop Genetics thinks it will have no such problems. A year and a half ago, John Henry, the firm's founder and chairman, formed an advisory group of former government officials, including two former EPA commissioners, to help the company pave the way for the proposed experiments.

"They told me to get out there and tell political leaders what we're doing," Henry said. "Anything new has a certain anxiety associated with it. People shouldn't read about this first in the newspaper."

For the past several weeks, Crop Genetics has been conducting a public relations campaign in Queen Anne's County and the Beltsville area, briefing county officials, state legislators, environmental groups and members of the staffs of local congressional representatives on its plans. Public meetings are planned for next year. Henry says he may even give demonstrations of the firm's technology to local high school science classes. The aim of all this is to persuade Marylanders that what Crop Genetics plans to do on two one-acre cornfields poses no threat.

"We've been talking to everyone who's in a position of leadership," said Henry, who adds that so far the company has had "nothing but a positive reaction. A very positive reaction."

Crop Genetics isn't the only biotechnology company convinced that grassroots lobbying is the best way to reduce emotions surrounding the release of manmade microorganisms. With dozens of companies lining up to take their bioengineered creations out of the laboratory, there is a new savviness about how to sell biotechnology experiments to a skeptical public.

In rural Wisconsin, near the small town of Arkansaw, Biotechnica International Inc. of Massachusetts has been working with local farmers and officials for almost a year in preparation for an outdoor test next spring of genetically engineered organisms designed to increase alfalfa yields.

"Most of the community, even if they started out skeptical, are supportive now," said David Glass, Biotechnica's director of patent and regulatory affairs. "I think we've avoided the kind of hysteria shown in other communities."

Last month in South Carolina, following a public relations blitz, chemical giant Monsanto Co. ran the nation's third outdoor experiment with genetically altered bacteria without a hint of public opposition.

"In the course of the next few years, these kinds of experiments will become commonplace," predicted Howard A. Schneiderman, a senior vice president of Monsanto.

Biotechnological research and public opinion first crossed swords 11 years ago in Cambridge, Mass., where some of the first gene-splicing experiments were being conducted at Harvard University. Concerned that researchers had begun potentially dangerous experiments in the school's laboratories without notifying the community, Cambridge Mayor Alfred Velluci invoked images of Frankenstein in imposing a six-month ban on the research.

Since then, the scientific community has attempted to calm opinion with evidence attempting to show that biotechnology experiments do not pose serious potential hazards.

In the past few years, federal regulatory authorities have worked out regulations to govern outdoor experiments. Before a company can go ahead with a test, it has to provide the EPA with data on its product's toxicity and mobility: How does it affect nontarget plants and animals? What does it kill? Does it multiply and spread beyond the test site?

Crop Genetics believes it can pass those tests. Peter Carlson, the firm's chief scientist, has developed a method of splicing a natural chemical known as bacillus thuringiensis (BT), which is fatal to the corn borer, into a microorganism that lives within the corn plant. When the corn borer, a chronic pest difficult to control by conventional chemicals, attacks the stalk, it dies. In effect, the Crop Genetics technology gives corn plants their own built-in pesticide.

The firm has to prove to the EPA that BT is deadly only to caterpillars. Henry said that has been relatively straightforward because the BT bacterium has been used in home gardens for years and has never been thought of as having harmful side effects. Crop Genetics scientists also believe that the microorganism's mobility is negligible, since it cannot survive outside the corn plant.

As the industry and the regulatory climate have matured, the public's initial fears about biotechnology have subsided. A poll done for the Office of Technology Assessment by Harris & Associates a year ago showed that 62 percent of the public felt that the benefits of biotechnology outweighed the risks.

But some traces of the initial public skepticism remain. The Office of Technology Assessment found that while a large majority of the public favored environmental release of genetically altered organisms in small-scale experiments, that figure was halved when there was insufficient public information about the potential risks of the proposed experiment.

"If products have a clear benefit, people will accept them," said Allan Goldhammer, Director of Technical Affairs for the Industrial Biotechnology Association in Washington. "But you can't take the public for granted. You have to sit down and explain things to them. They're very easy to scare, and it's much more difficult to mollify them the second time around."

For instance, local officials in California's Monterey County in March 1986 blocked a pioneering outdoor test by Advanced Genetic Sciences of Oakland of a genetically engineered bacteria to guard strawberries from frost. They say they acted not out of fear of biotechnology but in reaction to what they described as the firm's arrogance.

"The people at AGS refused to provide any significant information to the Board of Supervisors or to the public until they were forced to. It was like pulling teeth," said Marc Del Piero, the Monterey County supervisor who led the opposition to the proposed test. "They had a total ignorance of local land-use procedures and no sense that they had any responsibility to the community. They took the position that the public didn't have the right to know. They wouldn't even tell us the exact location of their test."

Advanced Genetics Sciences completed its test in April, despite some sabotage, after moving the test to Brentwood, Calif., 60 miles east of San Francisco. In preparation for that test, the company hired public relations consultants to open doors in the community, held town meetings and briefed local officials.

Monsanto had a similar experience last spring, when it halted a planned experiment in Missouri's St. Charles County after both the EPA and local government officials had objections.

"We didn't give it the full-court press. We should have had a mobile unit out there," Schneiderman said. "We should have given out 1,000 copies of a videotape explaining our experiment."

To prepare for last month's successful test in South Carolina, Schneiderman said, "We learned from our failure." Monsanto sent in market researchers and dozens of staffers to deal with local concerns.

Monsanto also took more care the second time around in choosing the site of the test. "You have to find a community where the future depends on agricultural competitiveness," Schneiderman said. "You've got to go to a community where they understand agriculture. That's why we picked South Carolina."

That's also why Crop Genetics chose Maryland for its test. Corn borer infestation in the state has been particularly severe in recent years, destroying as much as 20 percent of a typical field of corn. Henry said he has found a receptive audience not only among farmers looking for a more effective means of coping with the caterpillars, but also among those concerned about the environmental toll of chemical pesticides.

"They're looking for an alternative to spreading so many gallons of chemicals on the land where it washes off into rivers and the bay, and that sounds very good to me," said Queen Anne's County Del. Jack Ashley, who met with Henry for an hour and a half several weeks ago. "My gosh, you never find out anything unless you try."

"The first question people always ask is, 'Why do you want to do the test here?' " Henry said. "I tell them that it's because we're here, and the European corn borer is here, and our technology is here. We're not about to run off to the Midwest to do this."

"They've done a good job of being up front," said Parris Glendening, Prince George's County executive. "My feeling is that as long as they are meeting all of the federal guidelines and controls and making a strong effort to reach out to the public, we should work with them and cooperate.