“The problems the commission found at LIPA are extremely troubling and some of them need to be further investigated by criminal prosecutors,” said Benjamin M. Lawsky, co-chairman of the commission. “Our extensive investigation uncovered breathtaking waste and inefficiency at LIPA that helped jack up rates for Long Island families.”

Over four years, the authority paid about $65 million to consultants, of which $28 million went to Navigant, the commission said. In 2010, Mr. Hervey signed a $23 million contract that extended Navigant’s utility contracting services for five years. The following year, he approved about half of the $7.2 million billed to the authority by Navigant, the commission said.

Navigant was by far the largest contractor to the authority in each of the years the commission studied, the report shows. But the investigators started taking a hard look at the firm only after discovering that Mr. Hervey had gone to work there so shortly after resigning from the authority, members of the panel said. They soon learned that other senior managers either had gone to work at Navigant or had worked at the consulting firm before joining the authority, they said.

The commission found that more than 50 consultants at Navigant billed the authority at rates of $300 to $500 an hour, the report states. It also found that some of the consultants billed the authority for more than 1,800 hours a year, with one of them charging for 3,500 hours in a single year — or about 70 hours a week.

According to the report, a single Navigant employee billed the authority more than $4.5 million for his work over five years; from 2008 through 2011, the authority paid more for his services alone than it did for those of any entire firm — legal, accounting, financial or other — the report shows.

The report also detailed travel expense reimbursements for Navigant consultants that it said were “exorbitant.” In one case, a consultant based in Washington billed for an unexplained trip to Puerto Rico that included a seaplane flight from San Juan to a resort island, it said.

In another, the authority reimbursed Navigant more than $6,800 for one consultant’s 11-day stay in a New York City hotel, well above the state government guidelines of a limit of $295 per day for lodging and a $71 per diem.