Attorney General Martha Coakley recommended Tuesday that the state fine NStar $9.7 million for failing to respond adequately to damage caused by two severe storms last year: Tropical Storm Irene and a rare October snowstorm that downed power lines across the state.

The storms left hundreds of thousands of customers without power, some of them for days, and sparked complaints that utilities were unprepared.

Two weeks ago, Coakley asked state utility regulators to levy a record $16.3 million fine against National Grid, the state’s other major energy utility. She has also pushed for a $4 million fine against a smaller utility, Western Massachusetts Electric Co.

Coakley said NStar, which recently merged with Northeast Utilities of Connecticut, failed to estimate the severity of the storms, communicate with customers and government officials, and respond to public safety calls about downed wires.

“NStar’s preparation for these storms was woefully inadequate and much of the power loss suffered by hundreds of thousands of customers could have been avoided,” Coakley said in a news release. “The company’s slow response to downed wires created a dangerous public safety situation for towns across the Commonwealth.”

NStar responded that it was one of the first utilities owned by shareholders to restore power to customers in both storms and even provided crews to help other utilities in the snowstorm.

The utility said it fully complied with a response plan approved by the state and therefore should not be subject to any penalties.

“The attorney general is alleging performance violations based on standards that do not exist,” NStar Electric president Werner Schweiger said in a statement.

The Department of Public Utilities launched formal reviews of the utilities’ response to the storms last year, but has not set a deadline to determine whether to impose any fines.

NStar serves 1.4 million customers in eastern and central Massachusetts, including more than 1 million electric customers in 81 communities.