Prince George's County Executive Jack B. Johnson lashed out at Washington Gas yesterday for what he called the utility's failure to keep county officials and residents informed of its investigation into the cause of thousands of natural gas leaks over the past two winters.

He also voiced concerns over the company's plan to fix the leaks by injecting additives into the imported liquefied natural gas it receives.

"The residents of Prince George's County and I are increasingly frustrated with the lack of information provided by Washington Gas and the company's failure to be concerned for the safety of the residents of Prince George's County," Johnson (D) said in a statement.

Washington Gas officials said they were puzzled by the comments.

"We don't understand the statement, given the close interaction we've had," company spokesman Tim Sargeant said.

Sargeant added that the company has participated in 19 public presentations since April 1 and provided monthly reports to Johnson and his staff.

The company attributes the leaks to the composition of imported gas, which it has said causes the rubber seals in underground pipe couplings to shrink. Officials hope that by mixing the gas with hexane and pentane -- heavy hydrocarbons lost during the liquefaction process -- or by blending it with domestic supplies, the additives will absorb into the seals, swelling and sealing the couplings.

The findings have been questioned by Dominion, which provides imported gas through its Cove Point facility in Calvert County. Dominion said the problem is poorly maintained couplings -- not gas composition.

Johnson criticized the company for being slow to inform the public of a sharp increase in leaks in December 2003, shortly after it began receiving the imported gas.

Johnson also said he was "very alarmed" that the gas industry knew since 1992 that changes in gas composition could cause couplings to leak. He was referring to a study that found the same problem in New York state after the Long Island Lighting Company began importing Canadian gas with lower levels of heavy hydrocarbons.

James H. DeGraffenreidt Jr., Washington Gas chief executive, said Thursday that the Long Island study was not well known in the industry. Washington Gas didn't become aware of it until after it began investigating the leaks, he said.

Washington Gas is carrying out a $144 million program to repair 1,400 leaks found in Prince George's and to replace approximately 111,000 couplings still in use.

The company said it might suspend replacement work once it tests whether the additives will stop the leaks.

Prince George's County Council Chairman Samuel H. Dean (D-Mitchellville) said he was satisfied with the Washington Gas response to the leaks and communications with officials.