WASHINGTON - U.S. Sen. Michael Crapo, the Idaho Republican arrested on suspicion of drunken driving, doesn't plan to fight the charges when he appears in court in January, a spokesman said Friday.

Meanwhile, results from a secondary blood alcohol test performed at the jail show the conservative three-term senator registered a higher level about an hour after being arrested than when he was first tested by the police officer who stopped him.

Police have said Crapo registered a blood alcohol level of 0.11 percent when he was pulled over early Sunday in the Washington suburb of Alexandria, Va., after running a red light. But a secondary test performed after Crapo was brought to the jailhouse - the one that will be used in court - registered at 0.14, nearly twice the legal limit, according to a law enforcement official with knowledge of the arrest. The official wasn't authorized to release information publicly and spoke on condition of anonymity.

"He does not plan to contest the charges," said Crapo spokesman Lindsay Nothern, adding that Crapo has consulted with a local Virginia attorney ahead of his Jan. 4 court hearing.

Nothern confirmed there had been a discrepancy in the blood alcohol tests, but said he was uncertain why they differed.

A blood alcohol level of 0.14 means Crapo tested 1/100 of a percentage point below the level that would have mandated jail time under Virginia law. The legal limit in Virginia, which has strict drunken driving laws, is 0.08 percent.

Crapo has apologized and taken responsibility for the incident in a statement, but he hasn't spoken publicly about the arrest. Crapo returned to Washington from Idaho on Wednesday as lawmakers pursue a solution to the looming fiscal cliff, but he wasn't immediately available to comment Friday.

A number of factors could explain the discrepancy between the preliminary breathalyzer test, performed on the street when Crapo was pulled over shortly after midnight, and the jailhouse test, conducted just before 2 a.m. The higher level at the jailhouse could indicate Crapo was drinking shortly before getting behind the wheel and his body was still absorbing the alcohol. But another possible explanation is that blood alcohol testing simply isn't a perfect science, said Michael Hlastala, a breath testing expert and former physiology professor at the University of Washington.

"It could be consistent with rising blood alcohol levels," Hlastala said. "But it just depends on the way the person was breathing, and other factors."

Alexandria police say Crapo was alone in his vehicle when he ran a red light, was pulled over and failed field sobriety tests. He was taken to the Alexandria jail and released on an unsecured $1,000 bond about 5 a.m. Sunday. Crapo is scheduled to appear in court on Jan. 4 - the day after the start of the next Congress. Crapo was handily re-elected in 2010 and won't have to run again until 2016.

It's still not clear where Crapo was coming from when he was arrested, and the senator hasn't explained the circumstances of the arrest. Court records show Crapo residing in Southeast Washington, a short drive over the Potomac River from the historic suburb where he was arrested.

The 61-year-old's arrest two days before Christmas stunned colleagues and constituents alike, not only because of his squeaky-clean image but also because the senator, a Mormon, had said previously he abstains from alcohol, in accordance with his church's practices.