After less than two years at the helm, Napa County Planning and Transportation Agency leader Jim Leddy is stepping down to take a job in Sonoma County government.

Leddy, a former aide to then-state Sen. Wes Chesbro, D-Arcata, took the reins of the agency in December 2006. He announced Thursday that he will become community and government affairs manager in Sonoma County.

“I have been touched by the incredible folks dedicated to improving the quality of life throughout the community and it has been an honor to serve with them through this position,” Leddy said in a farewell e-mail. “I am eternally grateful to the entire board of directors of NCTPA, the staff and the many community volunteers for my time here.”

During Leddy’s tenure, NCTPA expanded its mission from running the local transit service and formulating transportation policy to becoming a focal point for regional planning issues. The NCTPA board includes members of Napa County government and every local city council as well as private citizens.

This year the agency crafted a proposal for a countywide half-cent sales tax increase designed to pay for road improvements.

Voters rejected one transportation tax two years ago, and Leddy’s retooled effort focused more on road repairs than on new transportation projects.

But this summer, Leddy recommended to the Napa County Board of Supervisors that the tax measure, which would have appeared on the November ballot, be abandoned. Recognizing the likelihood that the measure would fail, the board agreed.

Supervisor Bill Dodd, who is also chairman of the regional Metropolitan Transportation Commission, praised Leddy for his work at the NCTPA.

“He has a lot of his expertise in legislative (matters) and his political acumen has served us well. He’s done a really good job in that regard.”

Dodd noted that the failure to get a transportation tax passed in Napa County is a disappointment, but said Leddy’s recommendation not to pursue a ballot measure this year was the right one.

Leddy said his new job will focus on helping Sonoma County address concerns regarding mental health care, juvenile justice, roads and managing county-owned property. He noted in an interview he lives in Santa Rosa, and so will be doing his part to help reduce carbon emissions.

He said NCTPA “has a lot of challenges coming down the pike,” including expansion of its “inter-jurisdictional role” in county politics and the quest for road improvement dollars.

“Additional resources from Sacramento and Washington are not going to come,” he said.

Leddy, who ran for state Assembly when Chesbro was forced out by term limits but lost in the primary to Noreen Evans, said he has no plans at this time to run for office again.

Both Leddy and Dodd said the county expects to ask former NCTPA director Mike Zdon to return on an interim basis and to help find a permanent successor for Leddy.

NCTPA employs 10 people, oversees the VINE transit system and controls an annual budget of $12 million to $14 million. Leddy’s last day at NCTPA will be Sept. 23.