HOLBROOK, Mass. (AP) _ For almost 75 years, townspeople paid little attention to the Baird & McGuire plant perched on a rise of the Cochato River wetlands.

Now residents stop at the 7-acre site to gape at 'round-the-clock guards in white protective suits and respirators. The guards keep people away from the benzene, arsenic, chlordane, dioxin and other toxic chemicals oozing toward ground water that once flowed clear to the river.

It is, officials say, a textbook example of the poisoning of America's land.

The site yielded hints for years: yellow-green pools of pollutants that children skipped through; a stench so strong that residents of a nearby housing tract occasionally complained to the health board; and early tests after which wells were closed because of contamination.

Nonetheless, some were surprised when the federal Environmental Protection Agency three years ago said it was among the 20 most hazardous waste sites in the country.

''Nobody ever said, 'Get it cleaned up, cut it out,''' said Selectman Frank W. McGaughey. ''It was so isolated, off in those woods. Half the people in town didn't even know it was there.''

There are few public records about the plant, which Dun and Bradstreet estimated to be worth nearly $600,000 in 1982, the year before it shut down.

It began life in 1912 as the Sterling Co., owned by James and Ella McGuire; it manufactured paints, waxes, oils and disinfectants. Two years later, when C.C. Baird became president, the company name changed to Baird & McGuire.

Sometime afterward, the plant switched to storing, packaging and distributing disinfectants, pesticides, herbicides and other chemicals.

In the postwar boom of the 1940s, a neighborhood sprang up at the bottom of the hill, attracting residents from around Boston to the wooded suburbs. Within a decade, the town had dug three water supply wells near the plant.

One well opened and closed in the same year. Tests by local health officials showed traces of ''unknown chemicals ... that caused an unpleasant taste in the water,'' The Holbrook Sun reported on Oct. 30, 1958.

''The water was so contaminated one week we couldn't even boil it,'' said a woman who has lived across the street from the plant for more than 40 years. The resident, who asked not to be identified, said, ''It smelled like disinfectant and it tasted like disinfectant.''

Over the next two decades, soil and water tests turned up such contaminants as chlordane, arsenic, lead, coal tar, kerosene and malathion.

The company tried new drainage methods and other remedies, but from 1974 to 1981 it was fined for numerous violations of chemical laws. In one instance, the EPA cited it for adulterating pesticides and mislabeling a shipment ''so that it bore a false and misleading statement.''

The state Department of Environmental Quality Engineering tested the three wells in 1980 and found several toxic chemicals, including benzene and chloroform. Two wells were closed.

In October 1981, a chemical tank explosion down the street from the plant prompted selectmen to inspect other tanks in town. They found chemicals percolating into the ground at the Baird & McGuire site and leaking into a river that fed a reservoir.

Heavy spring rains in 1982 washed chemicals from the plant into the river. The EPA fenced off the area; the following year the selectmen revoked Baird & McGuire's storage license. The company fought the order in court but later shut the plant down.

Those who saw it after the shutdown said the plant looked like a ghost town evacuated in an epidemic. ''The tanks were 50 years old, everything leaked, the retaining walls were falling apart,'' McGaughey said.

In 1983, one nearby resident, Rose Latini, filed a $51 million suit against the company. She claimed that while she lived on what was known as the Gill Farm, chemicals from the plant caused tumors she suffered and the cancer deaths of her husband, father and her father's two brothers, all of whom worked on the farm.

Thirteen other families have joined the suit, which is being handled by the San Francisco law firm of Melvin Belli.

Cameron Baird, head of the non-operating firm, and his attorney, Jeffrey Melick, said they would not comment because of pending litigation.

Meanwhile, two years of careful studies were carried out by the EPA, which was about to formulate a plan to clean up the area when dioxin was found at the site earlier this month.

The discovery set back the cleanup starting date by several months, and an EPA suit against Baird & McGuire to recover the costs of the multimillion- dollar cleanup could take years, said Paul G. Keough, deputy regional EPA director.

Keough warned against hysteria over dioxin, a byproduct in the manufacture of herbicides such as Agent Orange. Dioxin has been shown to cause cancer in laboratory animals but the extent of its toxicity to humans is only now being studied.

''If people don't eat the soil and stay off the property, there's no need for panic,'' Keough said.

The neighbor said she was skeptical of government assessments.

''They must have known it was bad before. Now they're blaming everyone but themselves,'' she said. ''Why didn't they do something about it in '55?''