Bob Doyle, just beginning his second term as Riverside County's sheriff, tendered his resignation Wednesday, to accept a position on California's parole board.

"The sheriff has informed the chairman of the board (of county supervisors) that he will retire within the next 30 days," Tom Freeman, the sheriff's executive officer, said Wednesday evening. He said he could make no further comment.

A member of the county's governing board said Larry Parrish, the county's executive officer, had notified top officials of Doyle's decision Wednesday afternoon.

A spokesman for Gov. Arnold Schwarzenegger, who reportedly made the state appointment, refused to confirm the report Wednesday, but said Doyle had referred calls to the governor's office.

Doyle did not return calls seeking an interview Wednesday evening.

County Supervisor Roy Wilson said Wednesday night he received a call from Parrish saying Doyle had decided to leave the county because the sheriff had been told he would be appointed to the state parole board.

Wilson said Parrish relayed that Doyle informed him of the development by telephone, but that the county had yet to be notified in writing.

"When it takes effect, we don't know," Wilson said, adding that the news caught him by surprise.

"I was shocked," he said. "I had no idea Bob would be thinking in that direction. Not that it is unusual. A state appointment is very prestigious."

The development was a surprise in large part because of the timing, coming less than a year into the sheriff's four-year term following his re-election in 2006. Doyle was due to serve until January 2011.

"We just expected to work with him for the next three years," Wilson said.

Asked about the process for filling a vacancy in that directly elected position, given an unfilled term, county spokesman Ray Smith said an election would not be required.

"If, hypothetically, a sheriff were to leave, my understanding is it would be an appointment by the Board of Supervisors to complete the term," he said.

The No. 2 position within the department -- undersheriff -- is held by Neil Lingle.

Supervisor Jeff Stone, who has clashed periodically with Doyle about jail issues, said Wednesday that he hadn't decided whether to urge the Board of Supervisors to appoint a replacement from within or from outside the department.

He said that, whoever the board names, he wants the appointment to improve the relationship between the deputies' union and department administrators and between the sheriff's office and the Board of Supervisors. Sheriffs are popularly elected, thus affording them a degree of independence, but the supervisors still must approve the department's budget.

Stone cited a recent FBI investigation of union officials, which he said had been politically motivated. Doyle was re-elected last year without the union's endorsement, Stone noted.

"There has been a uniquely contentious relationship between the sheriff and the union," Stone said.

Doyle was the undersheriff when he was first elected sheriff in 2002 and was a landslide winner for a second term in the June 2006 election.

Since becoming the county's top cop, Doyle has been credited with bumping up staffing levels within the department while decreasing the time it takes deputies to get to high-priority calls.

The Sheriff's Department has more than 3,000 employees and is responsible not only for providing law enforcement in all the unincorporated areas of the 7,300-square-mile county -- communities such as Wildomar and Menifee -- but also in the Southwest County cities of Temecula, Lake Elsinore and Canyon Lake, which contract with the department for police protection.

Doyle started with the Riverside County Sheriff's Department on Sept. 2, 1975, and has served as a deputy, investigator, sergeant, lieutenant and captain in areas throughout the county. He was a lieutenant and captain at the Lake Elsinore sheriff's station where he also served as station commander.

Before being appointed as the undersheriff in December 1999, Doyle was an assistant sheriff in charge of department operations for nearly five years. In that position, he oversaw patrol services countywide.

As the undersheriff, Doyle's responsibilities included all matters of department policy, budgets, resource allocation, deployment of personnel, personnel as a whole and organizational structure.

Doyle has a doctorate in management, a master's degree in human resource development and a bachelor's degree in public administration. He holds a lifetime teaching credential from the California Community College system.