FORT MONTGOMERY, N.Y., Oct. 26 - Twelve years ago, when a new gasoline additive held the promise of reducing air pollution, New York State made a huge bet that the technology would work. It supported the use of the additive, M.T.B.E., to be mixed with gasoline at some of the highest concentrations in the nation, from 12 to 15 percent, while also allowing the additive to be used in parts of the state where air pollution was less of a problem.

Talk about a David and Goliath scenario, and going from Bonac to Brockovich: Yesterday the East Hampton Town Board met with representatives from a prominent personal injuries law firm in executive session. Their goal was an exploration the likes of which few municipalities have undertaken. The uncharted territory? A lawsuit against the oil companies that manufacture the gasoline additive MTBE.

Twice a week, Dan Whalen drives a quarter-mile to fill 10-gallon jugs with drinking water from a tanker truck that's been supplying water to his neighborhood for more than two years.

Whalen, who lives in Hyde Park, Dutchess County, doesn't drink the water from his taps because the wells in his neighborhood were contaminated by one of the state's biggest spills of gasoline and MTBE, a highly toxic chemical additive. MTBE, or methyl tertiary butyl ether, is also a suspected carcinogen.

A GASOLINE additive intended to reduce air pollution, in large-scale use on Long Island for less than 10 years, is rapidly moving though the region's groundwater, penetrating drinking water supplies.

The additive, M.T.B.E., for methyl tertiary butane ether, has been found in the highest concentrations in shallow wells near gas stations and industrial areas where petroleum spilled. It is also being detected in nearly one in five of the deeper public wells that are the Island's principal sources of drinking water.

In gas leaks, state often decides not to tell

The bulldozers working at the corner service station caught Jason Hill's eye on a hot August morning in 1995. So did the truck that said "New York State Department of Environmental Conservation" in green lettering on the doors.

For years, the Hills had wondered why their washing machine smelled faintly of gasoline, and why they would get headaches and feel dizzy whenever they took a shower. And they didn't understand why their allergist couldn't find the cause for 11-year-old Jeanine Hill's chronic sinus infection.