By Shelby Sebens

PORTLAND, Ore. (Reuters) - Marijuana smoking, seed sharing and cannabis-themed rallies are among the ways Oregon residents plan to celebrate as recreational-use pot becomes legal in the fourth western U.S. state on Wednesday.

Marijuana use purely for the sake of getting high is to become legal in the state from midnight on Tuesday, the first step in a voter-approved initiative that will usher in retail weed stores in 2016 like those operating in Washington state and Colorado.

Pot shops are also expected in 2016 in Alaska, where voters in November backed a similar legalization initiative. Pot use became legal in Alaska in February.

The new laws reflect a shifting legal landscape for a plant that remains illegal under federal law. Campaigns for legal pot have started in California and other states, and medical-use cannabis is now allowed in nearly half of U.S. states.

"We are thrilled with the end of adult marijuana prohibition, but we are far from where we need to be," said Russ Belville, of pro-marijuana group NORML's Portland chapter.

Under the law, Oregon residents 21 and older can smoke privately, grow up to four plants and legally posses up to eight ounces (227 grams) at home and have one ounce (28 grams) outside home, the Liquor Control Commission said.

Driving while high remains illegal and pot cannot be transported out of state, even to neighboring Washington, where retailing started last year, the commission said.

Weed giveaways and rallies were planned for the week, and advocates planned to gather before midnight under the neon "Portland Oregon" sign to take photos and exchange pot seeds and flowers, an event organizer said.

In a subtle dig at stoned snackers, Portland police issued a graphic showing how much weed a person can possess by comparing the amount with a donut.

Regulators will start accepting business license applications in January, with stores slated for next fall.

Opposition was still simmering, though, with lawmakers pushing a bill allowing marijuana retail bans in municipalities where at least 55 percent of voters opposed November's ballot initiative, said Republican state Senator Ted Ferrioli.

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"Nervousness about marijuana sort of becoming normed in our society is widespread," Ferrioli said.

Kevin Sabet, president of anti-marijuana group Smart Approaches to Marijuana, said: "When most Oregonians realize this is about Big Marijuana making money, and they see child poisonings from THC gummy bears and candies go up, along with car accidents, they may have reservations."





(Editing by Eric M. Johnson and Eric Walsh)