PORTLAND, Ore. -- Multnomah County's sheriff failed his police certification test this week, meaning he will need to hit the books before returning to regular duties as the county's top cop.

Sheriff Bob Skipper, 70, must retake the written exam to avoid months of basic training that is usually required for police certification.

Skipper became sheriff in July 2008, taking the position he also held from 1989 to 1994. He returned to a sheriff's office that many considered to be in disarray.

While he was away from law enforcement, his certification lapsed. Initially, the state of Oregon planned to force Skipper to return to the police academy so he could perform the same four-month training as a new recruit.

Oregon legislators later overruled and tailored a measure to Skipper's situation. As a result, he must pass the written exam instead of going back to the police academy.

Skipper said he took a two-week refresher course to prepare for the test.

"I just let myself down by putting a little too much pressure on myself to pass that test," Skipper said. "It's been a long, long time. I've been a policeman for 35 years, but I haven't been taking tests for a long, long time."

Skipper said he needs to review topics such as traffic statutes and other requirements that he has not used in several years.

He intends to pass the test and remain the Multnomah County sheriff until at least 2010.