Cheyenne Fox attaches radio frequency tracking tags to maturing pot plants inside a grow house at 3D Cannabis Center in Denver on Dec. 31, 2013. A Washington Post poll shows support for legalizing marijuana has expanded in the District. (Brennan Linsley/Associated Press)

Support for legalizing marijuana has expanded dramatically in the nation’s capital, with residents who were split evenly on the issue four years ago now favoring sales of the drug for personal use by a ratio of almost 2 to 1, according to a new Washington Post poll.

Washingtonians of every age, race and ethnicity — teenagers and seniors, blacks and whites — registered double-digit increases in support of legalization. Overall, 63 percent are in favor.

Even among those who oppose legalization, nearly half support relaxing punishment for marijuana possession to a fine of $100 or less.

The survey comes amid other moves across the country to legalize pot. This month, Colorado allowed the first sales of the drug for recreational use, and the state of Washington is preparing to follow suit.

The poll places District residents significantly to the left of a closely divided nation. A new, separate Washington Post-ABC News national poll this week shows voters coast to coast split 49 percent to 48 percent on the issue.

View Graphic Support for marijuana legalization grows in the District

The numbers also came on the same day that a committee of D.C. lawmakers voted unanimously to take the first major step in decades to loosen the city’s marijuana laws by advancing a bill to reduce the city’s penalty for possession of pot from $1,000 and six months in jail to a $25 civil fine.

The full D.C. Council will begin considering the measure next week. If passed, the fine would amount to less than most city parking tickets and would run counter to the federal penalties of $1,000 and one year in jail for possession, which could still be enforced on the Mall and other federal properties within the District.

A band of District activists also has filed a ballot initiative that could move beyond the council’s effort to decriminalize marijuana by asking voters, possibly this November, whether marijuana should be legal, as it is in Colorado.

Majority support for legalization in the nation’s capital, home to the federal law-enforcement agencies that most adamantly oppose it, could hasten the arrival on the East Coast of a debate that has largely simmered in Western states. Ballot measures in Alaska, Arizona, California and Oregon this year could legalize marijuana in a contiguous, 1,800-mile swath stretching from the nation’s border with Canada to Mexico.

“There’s still a federal law that says it’s a no-no, and yet states are starting to legalize it. In my lifetime, what’s out west comes east. At this point, I think it’s inevitable,” said Richard Smith, a Northwest Washington businessman who deals in scrap metal.

At 68, Smith is among the 38 percent of District senior citizens who support legalizing marijuana — up from 26 percent in 2010. Smith says he simply no longer cares.

The initiative, which would require 25,000 signatures to qualify for the November ballot, would rival that in Colorado, allowing residents ages 21 or older to possess as much as two ounces of marijuana for personal use and to grow up to three plants at home. The initiative would also allow individuals to transfer, but not sell, up to one ounce of the drug, and it would permit the use and sale of paraphernalia. Because of federal oversight of District governance, the measure would have to go to Congress for review if passed.

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According to the Post poll, the expansion of support for legalization over the past four years is driven in part by a complete reversal of opinion among African Americans.

In 2010, 37 percent were in favor of legalization, and 55 percent were opposed. Now, that number has flipped, with 58 percent of African Americans in favor and 39 percent opposed.

In the past, many older black residents have opposed legalization out of the fear that it could lead to addiction among black youths. Those fears are reflected in the poll. Just 40 percent of black respondents ages 50 and older favor legalization, compared with 73 percent of younger black residents. There is no such age difference on legalization among white residents.

But the overall change in opinion could reflect the recent effort by civil rights groups to call attention to the disproportionate arrests of African Americans on marijuana charges.

A study that the Washington Lawyers’ Committee for Civil Rights and Urban Affairs released in July said nine out of 10 people arrested on the charge of simple drug possession in the city were black.

That report came on the heels of another from the American Civil Liberties Union, saying that the District is arresting more people than ever for marijuana possession: 60 percent more in 2010 than a decade earlier, with black residents accounting for much of the increase.

D.C. police say the majority of people arrested in the city do not live in the District. In addition, Police Chief Cathy L. Lanier has insisted repeatedly that her department doesn’t target African Americans or prioritize minor arrests ahead of serious crimes. The numbers are explained in part, she said, because more arrests tend to occur in higher-crime parts of the city with a greater police presence.

In Ward 1, which includes part of historically black Shaw but also Columbia Heights and Adams Morgan, African Americans accounted for 81 percent of the more than 1,200 drug arrests in 2011 — but make up about one-third of the population.

“I don’t care one way or another about legalizing it,” said Renee Matthews, 49, a Northeast resident who works as a receptionist at a teachers organization downtown. “But it shouldn’t be criminalized if the penalties are harder for African Americans.”

Charles Dorsey, 60, who lives off Benning Road in Southeast, agreed. “Marijuana is so prevalent. People are using it all over; there are no real medical harms in using it — liquor causes more harm.”

Still, African American women are among the least likely to support legalization, with 51 percent in favor to 45 percent against.

Chuquita Berry, a homemaker in the Marshall Heights neighborhood, said she opposes legalization and attempts to lessen penalties because she fears a rise in impaired driving as well as “major negative impacts” on her neighborhood.

“The law needs to remain the same,” said Berry, 34. “You could see the negative effects on children, teenagers, adults. It would create more of a problem.”

African Americans aren’t the only ones driving the trend. Their share of the city’s population has fallen below 50 percent over the past four years. Since the 2010 Census, the District’s population has mushroomed by 45,000 people, a 7.4 increase, with many newcomers young and white. More than three-quarters of white residents younger than 40 favor legalization.

One is Will Hardy, 34, who returned to the District after eight years away and is working at a Starbucks near Lincoln Park on Capitol Hill while he figures out a way to combine his loves of music and politics — perhaps by working on issues of royalties for artists.

“I smoke pot, and I’m a highly functioning critical thinker — perhaps not at Starbucks, but in my personal life,” Hardy said. “The prohibition on pot has been lost in terms of its social goal — to calm a social problem. It’s creating a social problem, not calming it.”

Under the bill approved Wednesday, fines would be lowered to $25. Those caught smoking marijuana in public could be fined $100 and have their paraphernalia confiscated; minors would also have a letter sent home.

“We know that 90 percent of those charged for small amounts are generally young African Americans,” said its author, council member and mayoral candidate Tommy Wells (D-Ward 6). “For those, a $25 fine and losing whatever paraphernalia will be an impact,” Wells said.

Wells said he thinks it would be prudent to monitor the rollout of legalized marijuana in Colorado and elsewhere for at least a year before making a decision on whether the District should go the same route — a step that would probably set up a confrontation with Congress over the issue.

As it is, the $25 fine for possession would rank the District behind only Alaska as the most forgiving as far as states that have elminated jail time for marijuana go. Seventeen states have done so.

Scott Clement, Mike DeBonis and Carol Morello contributed to this report.