When Carl and Marie Susinno moved into their house on Arctic Avenue in Rockville, their lawn had more weeds than grass. So they hired ChemLawn, the lawn service industry giant, to spray with pesticides and fertilize the lawn five times a year.

They have used a lawn service for 12 years. Now, however, Marie Susinno said she is having second thoughts over the amount and potential hazards of chemicals used in their yard.

"I talked to my husband about it recently," Susinno, 50, said Friday, only hours after ChemLawn had treated their yard. "I think there's enough chemicals in the ground to keep from having the service, but [my husband] wants the green lawn."

Carl Susinno is not alone. About 4 million American households, according to industry figures, want that suburban dream of a lush green lawn with little effort. Marie Susinno, on the other hand, is not unlike a growing number of persons who are worried about the health risks of lawn pesticides. That concern has prompted a number of local governments across the country to regulate applications by the lawn care industry, including a recent controversy in Montgomery County over the posting of signs during lawn treatment.

The key issue among those concerned is whether people, especially small children, the elderly, the ill and a small segment of the population that is hypersensitive to toxic chemicals, have a right to know when they are being exposed to potentially harmful pesticides so that they can take precautions.

No one knows for sure what level of exposure to pesticides can be considered safe. The National Academy of Sciences estimates that only 10 percent of pesticides have been tested thoroughly for long-term health effects.

Pesticides are designed to kill: bugs, weeds and fungus. The industry officials say that when these are applied properly, they are less toxic to humans than aspirin or coffee, and the officials maintain that it is perfectly safe to roll across grass three hours after it has been treated.

They emphasize that the pesticides are sprayed on in diluted form and are diluted even further by rainfall or watering the grass. The pesticides also are absorbed into the ground during the rain or sprinkling, and thus pose less of a danger, according to the industry experts.

Officials for ChemLawn, in fact, argue that their product is so safe that a consumer would have to eat 300 cups full of grass clippings that were treated by the company to equal the toxicity of one cup of coffee.

But health and environmental officials say most pesticides, which often can be absorbed through the skin, inhaled or eaten after they coat vegetables and other produce, lack adequate testing of long-term health effects and that some are suspected of causing cancer, nerve damage, birth defects and reproductive problems. They often counsel consumers to stay off treated lawns for 48 to 72 hours.

Critics of the chemical spraying of lawns point to the death of Lt. George M. Prior, a Navy navigator who died at Bethesda Naval Hospital in 1982.

His autopsy report said he died of multiple organ failure caused by toxic epidermal necrolysis, a burning of the skin caused by exposure to toxic chemicals.

An avid golfer, Prior became ill while playing at the Army-Navy Country Club. His wife said that 10 days later he was dead, after blisters the size of baseballs had torn 80 percent of his skin from his body and his kidneys, lungs, liver and heart failed.

In a $20 million lawsuit filed in Arlington County Circuit Court in 1983, Liza Prior contends that her husband's illness and death resulted from exposure to Daconil, a fungicide commonly used by lawn care companies and golf courses to prevent brown spots on lawns.

Gary Klein, an official of the manufacturer, said the chemical was not responsible for Prior's death.

Montgomery County officials are attempting to join an estimated 40 other towns or counties from Maine to Oregon that have enacted ordinances to regulate pesticide application by the growing chemical lawn care industry, which had gross receipts of $1.5 billion last year.

Most of the local laws restrict the use of certain pesticides or require commercial applicators to post public warnings when pesticides are being applied.

Homeowners who pay lawn care companies $175 to $200 for up to six chemical applications usually do not know what chemicals are being used. Hydro Lawn in Gaithersburg provides customers with a list of products and safety precautions, but most companies do not.

Nearly two years ago, members of the Springfield Garden Club petitioned Montgomery County Executive Charles W. Gilchrist to seek legislation ordering lawn companies, which apply an estimated 270,000 chemical treatments to county lawns annually, to post warning signs during treatment.

The lawn companies formed FARE, the Federation Against Regulatory Excess, to fight the effort. "It's not so much that we're opposed to the idea of signs but because we didn't feel there was any actual factual proof that they were needed," explained federation spokesman Greg Dolan. "It's just the perceived feeling that a sign is going to be taken as a warning. It points the finger that there's a need for fear . . . . "

Last month, after efforts to reach an agreement with the companies, Gilchrist proposed legislation requiring that signs be posted when a lawn was being treated to advise people to stay off it temporarily.

The proposal would also require companies to tell customers what chemicals were being used and make warning signs available to homeowners who apply similar pesticides themselves. Hearings on the legislation will be scheduled later.

Montgomery County government agencies, along with the Washington Suburban Sanitary Commission, have begun posting signs in public spaces, indoors and out, when pesticides are being used.

Other counties in the Washington area have taken no similar steps, but officials in those jurisdictions say they are watching the Montgomery experience with interest.

Although a variety of chemicals are used to treat lawns, one of the most widely used is the controversial herbicide 2,4-D, one of two chemical components of the defoliant Agent Orange, which was used in Vietnam. Two less controversial ones are benomyl and dicamba, which tests have shown have a lower toxicity level than some of the chemicals used.

This year, Congress may attempt a major overhaul of the law that regulates pesticides, known as FIFRA, the Federal Insecticide, Fungicide and Rodenticide Act of 1947. But the chemical lawn care industry is unlikely to get direct attention from Congress, according to congressional committee staff members. More likely is a debate on whether local governments, such as Montgomery, have the right to impose pesticide regulations that are stricter than federal and state laws.

"When you've got 80,000 different government subunits out there in this nation, and you've got80,000 different pesticide regulatory schemes, the ability to use pesticides is going to be very difficult," said David H. Dietz, program director of the Pesticide Public Policy Foundation in Salem, Ore., a group backed by 2,400 pesticide manufacturers and commercial users.

Dietz, whose group has challenged some local ordinances in court and lobbied against enactment of others, said the industry will push Congress to make it clear that local laws should not go beyond state and federal regulatory requirements.

But the Campaign for Pesticide Reform, a national coalition of environmental, consumer, labor and farm lobbying organizations, plans to push for tougher pesticide regulations, including strong community right-to-know provisions.

Under current law, the Environmental Protection Agency approves pesticides after safety and health effects test data is submitted to the agency by the pesticide manufacturers. Central to EPA's control over pesticide use is the federal label that includes use instructions and precautions for farmers and homeowners who buy commercially available products.

But if a homeowner chooses to have a company treat his or her lawn, "you're not getting the opportunity to read the label," said Ellen Silbergeld, a toxicologist with the Environmental Defense Fund. "It's not even clear whether the applicators read these labels before they come to your house."

The EPA has delegated the licensing of professional pesticide applicators to the states, where regulations vary. In Maryland, for example, lawn care companies are required to employ at least one certified applicator who is supposed to supervise other company employes who apply the pesticides. The businesses are registered with the Maryland Agriculture Department. Most lawn care companies train their applicators.

Environmental officials are particularly worried because the chemical lawn care industry, which did not exist 20 years ago, is growing rapidly as more families opt for the convenience. The industry is growing 25 percent a year in the Washington area and nationally, industry officials estimate.

"This is a new and very intensive segment of the business, and it's a segment that's outside the training, safety and other programs that have grown up around the agricultural use of pesticides. Lawn care companies . . . don't get the benefit of extension agents or Department of Agriculture guidance," said the Environmental Defense Fund's Silbergeld.

William Eichbaum, assistant secretary for environmental programs in Maryland's Department of Health and Mental Hygiene, noted that "the farmer is spending money to produce a crop -- the lower his pesticide use the lower his cost." The homeowner, on the other hand, "is buying a green lawn and is willing to pay for it. If more pesticide makes it greener . . . there's no incentive to use less."