The White House legislative affairs operation is facing extensive turnover as President Bush prepares one of the most ambitious second-term agendas ever to be seen on Capitol Hill.

Top House lobbyist Daniel Keniry on Friday became the third senior White House lobbyist to announce his departure since the November election.

The White House announced Friday that Brian Conklin, a former member of Bush’s House liaison team, will be returning to take over operations for that chamber.

Keniry’s decision to leave follows closely the departures of David Hobbs, who ran the liaison operation the past two years, and of Eric Pelletier, the “inside deputy” under Hobbs who recently took a job with General Electric in Washington.

Pelletier’s post has not been filled.

The departures have come amid mounting Republican concern that the administration has been overshadowed by critics of Social Security reform and other major policy initiatives, in part because the White House moved too slowly to get the new liaison operation operation up and running.

“The new folks are still waiting for their uniforms. Meanwhile, we’ve lost the tip-off and the first two in-bound passes and then called a time-out,” one White House ally said.

“Leaving as late as [Hobbs] did and not replacing him faster has really put Candace behind it,” the source added, referring to Hobbs’ successor, Candi Wolff. “They’ve really got to step up and take charge there.”

The source suggested that recent comments by Ways and Means Chairman Bill Thomas (R-Calif.) appearing to dismiss the administration’s plans for Social Security showed that the White House is paying a price for not staffing its lobbying operation more quickly.

A White House aide, however, noted that both Hobbs and Keniry have remained in their posts while awaiting the new hires. The aide argued that the concerns among allies are misplaced.

“If the individuals [Hobbs and Keniry] are still serving in their positions, I don’t see where there would be a lapse,” said Erin Healy, a White House spokeswoman. “There will be a smooth transition from one to the other.”

House GOP aides have pointed to more parochial issues. They note that Wolff and the three other White House aides who are pitching Social Security reform — economic advisers Charles Blahous, Keith Hennessey and Brian Reardon — are Senate alumni.

Hobbs, by comparison, had deep roots in the House from his long tenure as chief of staff to former Majority Leader Dick Armey (R-Texas).

Conklin and Wolff, who served as Vice President Cheney’s top Congressional lobbyist during Bush’s first term, have been well-received by allies of the White House.

“Candi’s a superlative choice,” said Dirk Van Dongen, a leading business lobbyist who has worked closely with the administration in its efforts to cut taxes. “She knows the Senate like the back of her hand, and she’s very well liked.”

Wolff served as deputy staff director for policy at the Republican Policy Committee under Sen. Larry Craig (R-Idaho), before leaving to join the administration in 2001. Both Wolff and Conklin are returning to the administration from a stint at the lobbying firm Washington Council Ernst & Young.

White House legislative affairs postings are known to be “burn-out” jobs, matching high-pressure environments with an exhausting work schedule. It is largely for that reason that the operation’s leadership often turns over after Congress reaches its second-year adjournment.

The departures of Hobbs, Keniry and Pelletier leave Matthew Kirk, the office’s top Senate lobbyist, as the lone holdover from the top echelon of Bush’s first-term lobbying staff.

“You strap yourself in at 7 a.m. Monday morning and hit the igniter. You go nonstop for a week. Then next Monday you do it again,” said Charles Brain, a lobbyist who served as President Bill Clinton’s final legislative affairs director. “It’s been described as a great rear-view mirror experience. The further away you get from it, the better it looks.”