Under pointed questioning Monday by the state attorney general’s office, NStar officials defended the company’s response to Tropical Storm Irene and last year’s October snowstorm.

Seven company officials spoke at an all-day hearing before the Department of Public Utilities, which is investigating the storm responses of NStar and two other utilities. The storms left hundreds of thousands of local residents without power.

The absence Monday of Paul Vaitkus, a former NStar executive, prompted swift criticism from the attorney general’s office.

“NStar’s ability to answer questions will ­obviously be limited because of the executive’s absence, which was not disclosed until last week, and we made clear our objections at the hearing this morning,” Attorney General ­Martha Coakley said in a statement.

Vaitkus retired in May as the company’s vice president of electrical system operations and transmission development. He is attending his daughter’s wedding this week, according to a June 14 letter from NStar to the DPU.

Craig Hallstrom and Stephen Sullivan, current vice presidents of electric operations who ­attended Monday’s hearing, “are extremely qualified to represent [NStar],” company spokesman Michael Durand said by phone Monday afternoon.

During Monday’s hearing, Assistant Attorney General Charlynn Hull asked Richard Tobin, NStar’s manager of emergency preparedness, about the company’s drill exercises.

NStar conducted two annual response drills in the spring of 2011, Tobin said.

In April last year, an outside company led a simulation of a Category Three hurricane, and in June of 2011 NStar conducted a logistics exercise.

The utility last conducted a full-scale hurricane response ­exercise in 2009, Tobin said.

“Hindsight being what it is, 20-20, do you wish you had done more training with respect to a Level Five or even a Level Four event?” Hull asked.

“I can’t say we would be any more prepared,” Tobin said.

“We train our employees every day to respond to events.”

Hull also questioned Sullivan about NStar’s efforts to protect power lines from overgrown and dying trees.

Sullivan said the company aggressively trims and clears trees where it has the legal right to do so.

“There was no correlation between date of last trim and the effects of those storms,” he said.

He said many of the downed trees that had caused outages during Irene and the October storm had been healthy and at a reasonable distance from power lines.

Referring to the October storm, which dropped more than 30 inches of snow in Plainfield, he said the early heavy snowfall on trees that still had leaves contributed to the large number of trees and limbs falling on power lines.

The DPU will hold hearings related to NStar’s actions every day this week at South Station.

Possible consequences for the utilities include fines and new rules.

“This investigation is a top priority for the department,” said Catherine Williams, a DPU spokeswoman.

“They are looking to resolve this proceeding as quickly as possible.”