Gov. Thomas H. Kean summoned reporters hastily Tuesday night to disclose that detectable levels of dioxin had been found in only three of 31 samples of soil and dust from the neighborhood around the Diamond Alkali Corp. plant, where employes labored around the clock to make Agent Orange during the Vietnam war.

Earlier tests from the plant site itself had found levels as high as 1,100 parts per billion, more than three times the concentration that led to the $33 million buyout of Times Beach, Mo.

Kean said the latest results were cause for "guarded optimism," and he went to a neighborhood bar in Ironbound, a downtown industrial section, to pass the word to the residents.

The curbside site that showed the highest level of dioxin, 5 parts per billion, will be cordoned off, he told them, and hundreds more samples will be taken in coming weeks. No one, he told the crowd gathered at the Lisbon At Night Tavern, will be evacuated against his will.

Then he bought the house a beer.

"It was good news only because we thought it would be so much worse," said a spokesman for the state's Department of Environmental Protection.

Ironbound is an extreme example of the problems that face New Jersey in an era of mounting concern over chemical poison. The Garden State has 65 sites on the Environmental Protection Agency's high-priority list for superfund cleanup, far more than any other state. It also has the highest population density of any state in the nation.

And along its eastern edge, from the E.I. Dupont de Nemours & Co.'s huge Chamber Works in Deepwater north along the New Jersey Turnpike to Newark, lies "cancer alley," a term applied when a 1976 National Cancer Institute study found that New Jersey had the highest overall cancer rate in the nation.

State officials concede that New Jersey's lucrative chemical industry has created health problems. "It's what it leaves in the state that has us concerned. And I don't mean money," said James Staples, a Department of Environmental Protection spokesman.

But Staples contended that much of the state's bad image results from its own vigorous effort to protect its citizens.

"As we keep plaintively saying, we started looking before anybody else did," he said. "Some southern states, with huge petrochemical complexes, won't even look."

Diamond Alkali is the first of nearly 50 sites in New Jersey slated for dioxin testing because of their history of manufacturing, blending or handling chemicals known to carry dioxin as an impurity.

Before Diamond Alkali employes manufactured Agent Orange, they produced the herbicides 2,4,5-T and 2,4-D, the two main ingredients of the wartime defoliant.

Technicians already have begun collecting samples for the next round of tests, from a weedy lot in Edison that once was home to a firm called Chemical Insecticides. The company, bankrupt since 1970, produced 2,4-D.

The technicians wear gas masks and the white protective overalls that have become a symbol of a nation's new awareness of the hazards of its chemical past. Yet for the last eight years, shorn of its buildings, the lot has been a playground for neighborhood children.

In Ironbound, where not one of the residents accepted Kean's offer of alternate housing while the dioxin tests are being done, there is another point of view.

Tom Smolenski, sitting disconsolately atop an outdoor wooden counter that used to display the fresh produce his family has been selling in the Ironbound farmers' market for 40 years, says business is off 95 percent. The state agreed Sunday to let the market reopen only if the produce were kept in trucks or behind protective plastic screening.

"It's been five days now. It's about time to get back to normal, especially since it's not what it was made out to be," Smolenski says.

Across the market, at Al's Bar and Grill, Raymond J. Hayducka says the whole episode is a "crock."

"I worked in the chemical plant for 16 years," says Hayducka, 37, who was reared in Ironbound and now works at the Cellomomer Corp., just down the streeet from the Diamond Alkali site. "I've never been sick."

Hayducka says his father died of cancer at 64. His sister, too, is dead of cancer. She was 29.

"But so what? My wife's sister died of cancer at the same age and she grew up three or four miles from here," he said.

"What're they going to do? Where are you going to hide New Jersey?" Hayducka said. "I won't waste my time worrying about it."