Three protesters who crossed police lines at the Boulder campus were arrested for trespassing and about 11 others cited, but a confrontation thought possible between protesters and police never materialized.

"This is a multiyear effort but the consensus is right now that we took a major step in ending this event," university spokesman Bronson Hilliard said, referring to the hundreds of participants this year versus 10,000 last year.

The event is held every year on April 20, on a date corresponding with a numerical 4/20 code widely known within the cannabis subculture as a symbol for all things marijuana.

University of Colorado administrators, saying they would no longer tolerate the annual gathering of pot smokers, sought to bar outside visitors to its flagship campus for the day.

At the start of the day police and campus security took up positions at entrances to the campus, refusing entry to people who could not show student or staff identification.

A field typically used for the "smoke-in" was ringed with police tape and three men were arrested after they crossed that barrier, holding signs that read: "Have a happy 4/20/1984" and "A violation of 1st Amendment, the right to peaceably assemble."

The 1984 reference is to the George Orwell novel of the same name that portrays an absurd and draconian totalitarian state.

"This is egregious. Why didn't the university open up a dialogue with us and ask what we think about marijuana?" said Gabriel Kuettel as he was being placed in a police vehicle.

But later police stood aside as a group of several hundred marchers approached the campus and made their way to another field, where they began smoking marijuana.

PROTESTERS MARCH IN OAKLAND

"We're not hurting anybody," a 19-year-old student, who identified himself only as Dylan, said as he smoked a joint. "With all these cops on campus there's more guns than ever before."

The throng dispersed less than an hour later. Police said the three protesters taken into custody faced a maximum penalty of six months in jail and a $750 fine. Ten other people were cited for trespassing and another for possession of marijuana.

In Oakland, meanwhile, about 100 demonstrators marched from a downtown federal building to the local headquarters of President Obama's re-election campaign where they delivered a letter demanding an end to the federal crackdown on medical marijuana businesses.

The marchers included one person dressed as a giant bong, another waving an upside down American flag, one wrapped in a plastic marijuana vine. A strong scent of marijuana smoke wafted through the crowd as speakers took turns lambasting the Obama administration for prosecuting marijuana users.

"I'm past anger to sadness," said Ellen Komp, 54, who manages the website for the National Organization for the Reform of Marijuana Laws. "I would like to be able to go into a bar and be able to have a joint instead of a drink, which I don't enjoy."

The march was led by Matt Witemyre of Local 5 of the United Food and Commercial Workers.

"We're here to protest the Obama administration's misguided politics when it comes to cannabis," Witemyre said. "He was elected on the promise to stop raids on medical cannabis and he has not done that."

About 100 UFCW workers lost their jobs on April 2 when federal agents raided Oaksterdam University, an unaccredited Oakland school that teaches marijuana dispensing and cultivation, along with related businesses, Witemyre said.

Peggy Moore, political director of the office, accepted the letter on behalf of the Obama campaign. "I will send it to our leadership," she said, declining to comment further.

A total of 16 states and the District of Columbia allow medical marijuana despite opposition from the Obama administration. No state currently allows recreational use of the drug, although Colorado voters will be asked to decide on recreational legalization in a November ballot measure.

(Writing by Dan Whitcomb; Additional reporting by Laird Harrison in Oakland and Emmett Berg in San Francisco; editing by Cynthia Johnston, Todd Eastham and Lisa Shumaker)

• A Permanent Economic Emergency