* About half of all Americans say they favor legalization
* Advocates say legal pot could boost tax revenues, jobs
* State, federal government laws must still be reconciled
* Tax revenues would be used in part to rebuild schools
By Samuel P. Jacobs
DENVER, June 2 (Reuters) - Throughout his presidency, Barack Obama hasn't exactly been a friend to marijuana users.
Sure, he has acknowledged smoking pot as a young man, but he has disappointed marijuana advocates by opposing its legalization, regulation and taxation like alcohol.
And the Justice Department's occasional crackdown under his administration on medical marijuana dispensaries, which 17 states and the District of Columbia allow, has angered others.
So now, with Obama facing a stiff challenge from Republican Mitt Romney in the Nov. 6 election, it's ironic that his chances of winning the key state of Colorado could hinge on marijuana legalization, supported by a growing number of Americans.
At issue is whether Obama will get a boost from young voters expected to be among the most enthusiastic backers of a Colorado ballot initiative that would legalize possession of up to an ounce of pot for recreational use - and give the state the most liberal marijuana law in the nation.
The initiative is a reflection of Colorado's unique blend of laid-back liberalism and anti-regulation conservatism that helped make the state the birthplace of the Libertarian Party.
It's a state where people of different political stripes see marijuana laws as an example of government needlessly sticking its nose where it doesn't belong.
It's also a proving ground for advocates who see legalization as a way to ease crowding in prisons, generate much-needed tax revenues, create jobs and weaken Mexican cartels that thrive on Americans' appetite for illegal drugs.
The Rocky Mountain State already allows the use of marijuana for medical purposes such as severe pain relief, and some communities have embraced it enthusiastically.
The prevalence of medical marijuana dispensaries in Denver has moved pot into the mainstream in Colorado's capital city.
In Denver County, home to about 600,000 people, one in every 41 residents is a registered medical marijuana patient, leading to chuckles about the "Mile High City." Denver is roughly a mile above sea level.
The number of places licensed to sell medical marijuana products has reached 400 here, according to the Denver Post. That means there are more dispensaries in the capital than there are Starbucks coffee shops (375) statewide.
A similar bill is on the ballot in Washington, another state that already allows use of medical marijuana. If approved, the initiatives would put the states squarely in the crosshairs of federal law, which classifies cannabis as an illegal narcotic.
PATH TO THE WHITE HOUSE
It's unclear precisely how the U.S. Justice Department - whether led by Obama or Romney - would respond if Colorado, Washington or other states legalize marijuana for recreational use. Both politicians oppose legalizing the drug.
But in a close presidential election in which Colorado could be a tipping point - and with polls showing Obama has up to a 30-point edge over Romney among voters age 30 and under - the state's marijuana initiative could be a factor if it inspires waves of young voters to cast ballots on Nov. 6.
"This is an issue that is really meaningful to young people, people of color, disenfranchised communities," groups that typically lag in registering and showing up to vote, said Brian Vicente, 35, executive director of Sensible Colorado, a group seeking less restrictive marijuana laws.
"Democrats and Obama need these groups to win," Vicente said. "The path to the White House leads through Colorado. We feel we can motivate these groups."
Last winter, Public Policy Polling found that 49 percent of Coloradans favored legalization, while 41 percent opposed it.
As much as some Democrats feel they have the wind at their backs, they are fighting history in Colorado. Obama won the state in 2008, but he was the first Democratic presidential contender to do so in 16 years.
And even though a majority of the delegates at the Colorado Democratic Party's convention last month said they supported legalization, some party officials are skeptical the politically diverse movement will help Obama much this fall.
They note that Colorado voters rejected such a legalization measure in 2006, and that Californians blocked a similar initiative two years ago.
"If they get 40 percent" of voters supporting legalization, "they should throw themselves a party," said Matt Inzeo, spokesman for Colorado's Democratic Party.
Others see more potential in the legalization debate's impact on the presidential race.
Tom Jensen of Public Policy Polling said that if the state-by-state race for the 270 electoral votes needed to win the presidency comes down to Colorado's 9 electoral votes, marijuana "could be a difference maker."
During a recent visit to Colorado, Romney seemed irritated when a local television reporter quizzed him on his views about gay marriage, immigration reform and marijuana legalization.
"Aren't there issues of significance you'd like to talk about?" an exasperated Romney asked.
In Colorado, however, marijuana is significant. And its acceptance hasn't been limited to more liberal areas.
Colorado Springs, home to the U.S. Air Force Academy and the evangelical Christian group Focus on the Family, is one of the most conservative cities in the United States. But the city of 400,000 about 70 miles south of Denver has nearly as many marijuana dispensaries as churches, according to city records.
Supporters of Colorado's initiative point to a broadening coalition of those who support legalization, including local civil rights and union leaders.
Those opposing marijuana legalization often cite the drug's impact on youths.
Roger Sherman, a strategist for the campaign against Amendment 64, said "there's a tremendous amount of enthusiasm and a high level of concern" among those who oppose legalization. His group cites increased drug use among children and increasing cases of impaired driving.
Nationwide polling on marijuana legalization, although sparse, suggests that support now equals support for marriage equality, which just found a new backer in Obama.
In October, 50 percent of Americans said "yes" when asked by Gallup, "Do you think the use of marijuana should be made legal, or not?" When Gallup asked that in 1969, 12 percent said yes.
Last week, a Rasmussen Reports survey said 56 percent of likely U.S. voters favored legalizing and regulating marijuana.
Supporters of legalization also argue that regulating marijuana - and capturing tax revenue from its sale - could help governments, cities and towns face increasingly tight budgets.
In 2011, taxes for medical marijuana generated $5 million for Colorado. Denver-based political strategist Rick Ridder said that depending upon the cost of an ounce, legalization would likely generate $20 million to $80 million in annual tax revenue for Colorado and local communities.
As designed, Amendment 64 would designate its first $40 million in tax revenue for rebuilding public schools. As part of a bond issue, that amount could turn into a treasure chest for public education funding in Colorado.
Legalization advocates see Obama's crackdown on some medical marijuana outlets as hypocritical, noting that in his memoir "Dreams from My Father" he acknowledged smoking pot as a youth.
"It's really insulting with this president. He actually smoked pot in high school and college. The only difference is he didn't get caught. If he had gotten caught, he would not be president," said Wanda James, 48, whose business, Simply Pure, supplies 300 Colorado dispensaries with edible marijuana.
She tells community leaders that legalization is not just about pot smokers having a good time, legally. She sees it as a way to ease prison crowding, help cash-strapped governments, provide jobs and weaken drug cartels.
Legalization, of course, would mean a larger market for James' indica sesame brittle bars and sativa peppermint cups.
To James, legalizing marijuana boils down to what could be a good slogan for this year's elections: "Jobs, jobs, jobs."