By Shelby Sebens

PORTLAND Ore. (Reuters) - Oregon's biggest county will no longer prosecute most marijuana cases after state voters voted this month to legalize the drug even as other prosecutors across the state take a more cautious approach, authorities said on Friday.

The Multnomah County district attorney, whose jurisdiction includes Portland, said that because recreational marijuana use by adults will become legal in July there is little point proceeding with marijuana possession or delivery cases.

"Because it is clear that a significant majority of voters in Multnomah County support the legalization of marijuana in certain amounts, this office will dismiss the pending charges related to conduct which will otherwise become legal," Multnomah County Chief District Attorney Don Rees said in a statement.

Oregon and Alaska voters decided in elections this month to legalize recreational marijuana use and usher in state-licensed retail shops similar to those operating in Washington state and Colorado, which became the first U.S. states to allow marijuana use for pleasure in 2012 ballot initiatives.

While Multnomah County is stepping back from marijuana cases, prosecutors elsewhere in the state are more hesitant.

"That's not going to be what we do in Marion County," Marion County District Attorney Walt Beglau said. "It's still against the rules in Oregon and under federal law. I feel it's premature to make any decisions given the law at this juncture."

Beglau said he expects to talk to local law enforcement officials in his county, which is home to state capital Salem, as well as other prosecutors across Oregon on how to best deal with the new law.

In Lane County, which includes Eugene, prosecutors said they had turned their focus away from misdemeanor marijuana cases long ago to focus on more serious felonies, but worried legalization would complicate policing in areas with drug problems.

"It's also bad news for the merchants, shoppers, students and parents who had hoped police would be able to clean those areas up, but it will have very little impact on my office," Lane County District Attorney Alex Gardner said.

Story continues

In Clackamas County, the state's third largest and a suburb of Portland, prosecutors said they expect to make a decision soon.

"We're still evaluating it," Chief Deputy District Attorney Greg Horner said, adding he did not have many pending cases that would fall under the new legal weed law. "This idea that there's this huge sea change of cases is just not accurate."

(Editing by Cynthia Johnston, Will Dunham and Sandra Maler)