Less than 18 months into his term, Virginia Gov. Robert F. McDonnell has been forced to revamp the office that develops and drives his policy agenda as he looks toward the most significant legislative session of his tenure.

His policy director left. So have both deputy directors. Virtually the entire policy office has turned over — a rare occurrence for any governor in such a short period of time.

McDonnell (R) announced a slew of new policy staff appointments last week and has reorganized the office, returning it to a structure employed by several previous governors. He also designated his counselor, Jasen Eige, to head both policy and legal matters.

It’s not uncommon for some staff members to leave a governor’s administration early because of high stress, relatively low pay and long hours, but many who worked closest with former senior policy adviser Eric Finkbeiner say they thought he would stay through the governor’s four-year term.

Finkbeiner’s departure this month came after almost a year of complaints about the office’s lack of communication, including no or little information on the governor’s proposals, unreturned phone calls and lower-level staff being kept in the dark about policy, according to lawmakers, staffers and lobbyists who spoke on the condition of anonymity because they did not want to anger the governor.

“I never felt Eric had the total grasp to manage that office,” said one Republican legislator.

McDonnell can point to meaningful accomplishments in his first two sessions, including $2.9 billion in bonds for perennially clogged roads and $100 million for underfunded colleges. But his proposal to privatize the state’s liquor stores suffered an embarrassing defeat at the hands of fellow Republicans, consuming months of his staff’s time as they tried to sell the proposal to lawmakers and residents.

McDonnell spokesman Tucker Martin did not respond to questions about specific complaints about the policy office or departures but instead touted the governor’s successes.

“The job of the policy office is to oversee the development and enactment of the governor’s policy initiatives,’’ Martin said. “Over the past two years, 86 percent of his proposals have passed the legislature. That’s a testament to the effectiveness and talents of the individuals in that office.”

Finkbeiner, who did not respond to repeated messages seeking comment, will return to McGuireWoods, one of Richmond’s most powerful and influential law and lobbying firms, where he was a senior vice president and a law partner.

His former deputy policy director, Mike Reynold, has been hired at McGuireWoods Consulting, the firm’s public affairs arm, solidifying the McDonnell administration’s already close ties to the bipartisan firm. Six members of the firm served on McDonnell’s transition team, including Frank Atkinson, chairman of McGuireWoods Consulting, and Richard Cullen, chairman of parent company McGuireWoods, friends of and donors to McDonnell.

“We do have a good relationship with the governor’s office,’’ Cullen said. “It’s very important we have a cordial relationship with state government, but we know the boundaries. We’re always at an arm’s length.”

McDonnell’s third legislative session kicks off in January with an almost entirely new team as he introduces his first two-year budget, allowing him to put his mark on policy for years to come, and months after crucial legislative elections in the fall, when he hopes to help Republicans win a majority in the state Senate. When McDonnell came into office in 2010, he inherited the budget of Timothy M. Kaine, which he could amend but not rewrite.

“This is his one and only budget,’’ Sen. R. Edward Houck (D-Spotsylvania) said. “It’s very important to his term and his legacy.”

Eige, who will join the Cabinet, was promoted to counselor and senior policy adviser to the governor, earning $152,000 a year. Six others will round out the policy office, including Eige’s deputy in the counselor’s office, Jeff Palmore, who will also serve as director of policy development, and Julia Ciarlo Hammond, who will be director of legislative affairs.

The departures began in December when Matt Bruning, special assistant for legislative affairs, became a lobbyist at the Virginia Bankers Association. Melissa Luchau, one of two deputy policy directors, left for a job at the Department of Education.

Reynold, deputy director of policy who also served as executive director of the Governor’s Commission on Government Reform and Restructuring, left Friday for McGuireWoods, where he will work on grassroots campaigns. Research assistant Kathleen Shannon resigned to attend law school.

Finkbeiner will return next month to McGuireWoods, where he will work on national policy initiatives, some for the National Governors Association and Republican Governors Association, of which McDonnell is vice chairman.

Some say gubernatorial staffers choose to leave before their term is up so they can use their influence before a governor’s term has ended, although they are prohibited by state law from lobbying the governor’s office for 12 months. Others say it has more to do with the hefty time commitments.

“Having been there, I think it would be odd if people didn’t leave early, considering the time and life commitments that it entails,’’ said Steve Horton, deputy chief of staff and director for intergovernmental relations for former Republican governor James S. Gilmore who left after three sessions and works at McGuireWoods.

During the past four administrations of Gilmore, George Allen and Democrats Mark Warner and Kaine, some policy directors left after two sessions, most after three. Kaine’s policy director stayed the full four years. But none saw a near complete turnover in their office in just over a year.

“Bob is a very demanding boss,’’ Del. David B. Albo (R-Fairfax), who has known the governor since the two served in the House of Delegates. “He has a lot of things he wants to get done.”

In nearly two dozen interviews, legislators, staffers and lobbyists say Finkbeiner’s departure follows complaints to Martin Kent, McDonnell’s chief of staff, and Phil Cox, the governor’s top political adviser, by lawmakers and contributors as early as last year.

Legislators say they were not given prior notice on McDonnell’s bills, including his proposal to bond nearly $3 billion for roads, and other important matters such as a lawsuit that resulted in Virginia lifting a long-standing ban on alcohol billboards.

They say Finkbeiner did not return calls to legislators and did not inform staff about legislative matters so they could help guide the governor’s agenda. Officials with state agencies did not show up to legislative committee meetings to answer questions, or more than one showed up and contradicted each other.

“Eric was a good adviser to the governor, but not a good manager of his staff,” one lobbyist said.

Cullen, who has known Finkbeiner for two decades, said he suspected Finkbeiner never planned to stay the full term, though he was doing a good job. “Eric was playing in the big leagues,’’ he said. “There is going to be criticism from time to time.’’

Luchau and Shannon did not return messages for comment.

Bruning said he hadn’t planned to leave within a year, but a job he was interested in became available. “I had an opportunity to join a great organization,’’ he said.

Reynold, who has two children under age 3, said he decided to leave after McGuireWoods approached him about a job. “It was where I wanted to end up,’’ said Reynold, who worked for McDonnell for four years.