By Courtney Sherwood

PORTLAND, Ore., Sept 22 (Reuters) - A former U.S. attorney for Oregon has endorsed an upcoming referendum to legalize recreational marijuana in the state and tax and regulate its sales, saying on Monday that laws banning the drug have failed to curb its use.

Kris Olson, who served as Oregon's chief federal prosecutor during the Clinton administration, is the latest public figure to endorse the ballot measure, which if approved by voters in November would allow recreational use of marijuana for those older than 21.

U.S. Representative Earl Blumenauer, a Democrat, and former Oregon Supreme Court Justice Bill Riggs have also both spoken out in favor of legalization.

"I enforced our marijuana laws, and they don't work," Olson said in a statement announcing her endorsement.

"Filling our courts and jails has failed to reduce marijuana use, and drug cartels are pocketing all the profits," she said, citing federal statistics that show about one in 14 Oregon arrests is for marijuana possession.

Meanwhile, the anti-legalization campaign, No On 91, reported its largest financial contribution to date on Friday. The Oregon State Sheriff's Association contributed $100,000 to efforts to defeat the initiative, according to campaign finance disclosures.

Recent polling indicates that the Oregon ballot measure is slightly favored to pass, though a similar effort failed two years ago.

Washington state and Colorado this year became the first two U.S. states to permit recreational sales of marijuana. Alaska and the District of Columbia will also decide on recreational marijuana measures in November. (Editing by Cynthia Johnston and Jim Loney)