D.C.'s proposal to decriminalize marijuana goes further than almost any other state in the nation, short of Colorado and Washington. PostTV explains the one-ounce rule in the legislation. (Theresa Poulson/The Washington Post)

Voters in the nation’s capital could decide if they want to follow Colorado and Washington state in legalizing marijuana under a measure cleared by the D.C. Board of Elections on Tuesday.

The decision sets aside warnings by the city’s attorney general, who said that if the proposal passed, it would put D.C. law at odds with federal law. The board’s decision allows a band of activists to begin gathering the 25,000 signatures needed to qualify the measure for the November ballot.

If the signatures are collected and the ballot measure passed, it could allow people 21 and older to possess as much as two ounces of marijuana for personal use and to grow up to three marijuana plants at home. The vote could also thrust the issue before Congress, which can block a city law by approving a joint resolution that is signed by the president. But Congress has done so only three times in 35 years.

Adam Eidinger, a leading activist for the initiative, has said he is confident his group can collect the signatures needed. He said Tuesday he was excited by the board’s decision.

Eidinger had hoped to station signature-gatherers outside polling places when the city’s primary election is held April 1. But the elections board has 20 days to settle on the language for the measure, so it is uncertain whether the petition effort can start that soon.

Support for marijuana legalization grows in the District.

If the measure does qualify for the fall ballot, it has a strong chance to pass, according to a recent Washington Post poll.

Support for legalization has expanded dramatically in the District. Residents who were split evenly on the issue four years ago are now in favor of allowing the drug for personal use by a ratio of almost 2 to 1. Washingtonians of every age, race and ethnicity — teenagers and seniors, blacks and whites — registered double-digit increases in support. Overall, 63 percent are in favor.

The elections board decision is the second major step in two weeks toward loosening the city’s marijuana laws.

Citing the goals of social justice and reducing racial disparity in marijuana arrests, the D.C. Council voted last week to decriminalize pot by imposing civil fines rather than jail time for most offenses.

Under that measure, possessing marijuana and smoking it in one’s home would no longer be criminal offenses, but would be punishable by a civil fine of $25. Smoking in public would be a misdemeanor equal to toting an open container of alcohol.

D.C. Attorney General Irvin B. Nathan last month urged the elections board not to go any further and to reject the proposed ballot initiative. He warned that legalization would put at least one aspect of D.C. law into conflict with U.S. drug laws.

But the elections board said in a statement Tuesday: “A ballot initiative is considered a proper subject if it does not appropriate funds, violate the Home Rule Charter, negate a Budget Act, or violate the Human Rights Act. In approving or rejecting a ballot initiative, the Board may only consider whether the measure meets these requirements.”

Nathan warned that under federal law, the city would still have to evict residents of public housing who are convicted of marijuana possession, even if D.C. law no longer considered possession a crime.

That’s a tension, however, that the city is already grappling with under the decriminalization measure, which Mayor Vincent C. Gray (D) said he intends to sign.

Eidinger appeared to have won over elections board members by arguing at a hearing last month that as written, the ballot measure would allow landlords the right to set terms of lease agreements, including prohibitions against possessing marijuana.

Many questions remain about how the measure would work in practice. The ballot measure would legalize possession of marijuana, for example, but not its sale, which would remain a crime.

Eidinger said the measure was crafted to minimize differences between D.C. and federal law to encourage the board to approve it for the ballot. He said that if it passes, he would encourage the D.C. Council to rewrite it and make it more practical to implement, including legalizing the sale and taxation of the drug.

Even some advocates, however, question whether the timing is right to push for full legalization in the District. They say legalizing the drug on the streets surrounding Congress and the very agencies charged with enforcing federal anti-drug laws would be too blatant a conflict and raise the likelihood that Congress would interfere.

As it is, once signed by the mayor, the D.C. Council bill to decriminalize marijuana must sit before a congressional panel for 60 days before becoming law. So far, there is little evidence that Congress would organize to block the measure.

It also remains unclear how overlapping local and federal jurisdictions would affect enforcement of decriminalization, particularly in national parks. Someone could still be arrested, for instance, for possession on the Mall.