PORTSMOUTH, N.H. — A New Hampshire company has begun an ambitious advertising campaign to persuade more Mainers to use natural gas rather than oil heat, which dominates the market. Northern Utilities Inc. of Portsmouth, N.H., has decided to become competitive in the home heating business, according to spokeswoman Shelly Dunn. “Our goal is to grow 5 percent per year over the next five years,” she said.

The month-old television and print marketing campaign — and a response to it from the Maine Oil Dealers Association — has led to one of the most contentious debates ever in this state about the relative safety, cost and environmental impact of the two fuel products.

About 60 percent of all Mainers heat with oil while less than 2 percent use natural gas. The remainder heat with electricity, wood, propane and kerosene.

Natural gas usage has been increasing steadily in America for two decades while oil use has declined, according to U.S. Census Department data. It is because of that that Northern Utilities believes it can sharply increase the use of natural gas in Maine.

Natural gas has fared poorly in Maine, partly because gas lines do not extend to northern Maine and some rural areas in southern sections.