National Grid, the giant British utility firm that distributes electricity in seven area communities, plans to reduce its total greenhouse gas emissions by 80 percent over the next four decades.

The company - which provides electricity to Attleboro, Foxboro, Norton, Plainville, Rehoboth, Seekonk, and Wrentham - had already set out a plan to reduce emissions by 60 percent over the same time span. But the utility's officials have now decided to aim for a four-fifths decrease.

"Minimizing our impact on the environment while delivering safe, secure and economic supplies of energy to customers is not an option, it is a must," National Grid's chief executive, Steve Holliday, said in a statement. "And the two have to be tackled together."

A key component of the company's plan for achieving the target is a new system of "carbon budgets," which will give executives and managers a set allotment for how much carbon their lines of business can emit annually.

The first set of carbon budgets will be drawn up next April, after a year-long review of the company's overall emissions. National Grid spokesman Chris Mostyn stressed that the new reduction targets will not have a negative impact on customers.

"To reassure everybody, security of supply is still key to us," he told The Sun Chronicle. "But there's no reason why we can't deliver gas or electricity safely and economically while also reducing emissions."

Mostyn also said National Grid and its predecessors have worked with their customers over the last 20 years to find more ways to conserve energy, an effort that has saved New Englanders more than $2 billion over time, he said.

National Grid entered the local market in early 2000, when it took over Mass. Electric as part of its purchase of the New England Electric System. The company says it now serves 1.2 million customers in 168 communities statewide.

Scientists say greenhouse gas emissions are the driving force behind climate change and must be reduced to prevent further damage to the environment. National Grid's carbon reduction pledge drew praise from Ian Bowles, the state secretary of energy and environmental affairs.

"National Grid is showing real leadership by reconciling its core utility business with dramatic curbs in greenhouse gas emissions," Bowles said. "In the 21st century, energy and environmental goals require alignment."

The company also wants to work with regulators, Mostyn said, to look for ways to eliminate the disincentive whereby companies that manage to increase their energy efficiency actually hurt their bottom lines, because less energy means less revenue.