BOSTON – Some power companies in the East are going on the defensive against criticism over the tens of thousands of lingering power outages nearly a week after Hurricane Irene swept up the coast.

NStar, a major utility in Massachusetts, took out a full-age ad in Friday’s edition of the Boston Globe with the headline “Goodnight, Irene.”

“Being ready for Mother Nature is one thing,” the ad read. “Responding to her is another. We know trees will come down. We didn’t know which ones.”

As of Friday afternoon, NStar said fewer than 3,000 customers in Massachusetts lacked power. Another big state utility, National Grid, expected fewer than 5,000 homes in the dark at the end of the day.

At one point, the state had more than 500,000 customers without power. They were among more than 9 million that Irene plunged into darkness from the Carolinas to Maine.

Utilities in many spots have been criticized by politicians and homeowners who say response times were slow and outreach efforts to customers poor. The companies have noted that Irene was an unusual weather event and that crews have been working around the clock.

In Washington, Pepco spokesman Clay Anderson said the company ran three radio advertisements before, during and after the storm.

The utility, which has some 778,000 customers in the District of Columbia and neighboring regions, considered running a large ad in Sunday’s editions of The Washington Post, thanking customers for their understanding during the storm.

In Baltimore and environs, where some 32,000 people still lacked power Friday afternoon, Baltimore Gas and Electric took out ads to thank customers for their patience and explain who would get power back first.

The company started running a 60-second ad this week on several radio stations, spokesman Robert Gould said.

“The impact is severe and widespread, including massive numbers of trees and large limbs that damaged power lines and other equipment,” the ad says in part, concluding: “Thank you again for your patience. Together we’ll weather.”

In New Jersey, where the hurricane made its second landfall and sent rivers over their banks twice in spots, Gov. Chris Christie says the state Board of Public Utilities will hold hearings on the performance of state electric companies after Hurricane Irene.

Jersey Central Power & Light will cooperate with any review of its performance, spokesman Ron Morano said.