The tax assessor for a Southern California county that's been hit hard by the housing bust was arrested Thursday after investigators found a substance believed to be methamphetamine at his home, authorities said.

Bill Postmus, 37, was arrested one week after he told San Bernardino County leaders he had overcome a substance abuse problem. The former chairman of the county Board of Supervisors was taken into custody at his Rancho Cucamonga home, said district attorney's spokeswoman Susan Mickey.

The investigation also yielded search warrants in other cities in Orange and San Bernardino counties, but Mickey said she couldn't specify how those were linked to Postmus.

Postmus oversees the setting of property values for tax purposes in the county of about 2 million people in the inland region east of Los Angeles. In 2007, the county reached an all-time high of nearly $173 billion in property value in 2007 — more than double the county's assessed value in 2000.

The county last year ranked as having the seventh-highest foreclosure rate in the nation.

Postmus could not be immediately reached for comment through his office. Ted Lehrer, spokesman for assessor's office, said he could not comment on Postmus' arrest, but said it would not affect the operation of the office, which employs more than 200 people.

In a statement, supervisors Chairman Gary C. Ovitt called Postmus' behavior "intolerable." He said he would be keeping "very close tabs" on the assessor's office and would keep daily contact with Assistant Assessor Dennis Draeger.

Last week, Postmus told supervisors he had beaten a drug problem and planned to finish his term, which is due to end in 2010. He said he would not seek re-election.

Ovitt said the board would vote on whether to remove Postmus from office at its Jan. 27 meeting.