BOSTON – Attorney General Martha Coakley has certified as constitutional 13 initiative petitions that seek slots on future statewide ballots, including those aimed at eliminating the state’s motor vehicle excise tax and decriminalizing small amounts of marijuana.Other initiatives seek to ban greyhound racing, limit the growth of property taxes, eliminate the state income tax, and repeal a law establishing a comprehensive permitting process for affordable housing projects. The proposal to decriminalize marijuana possession stipulates the amount must not exceed one ounce.In order to appear on the ballot, a petition must obtain the signatures of 66,593 registered voters by Dec. 5. Once accomplished, the proposal would be sent to the state Legislature to enact before the first Wednesday in May 2008.If the Legislature fails to enact the proposal, its proponents must gather another 11,099 signatures from registered voters by early July 2008 to place the initiative on the 2008 ballot, according to Coakley spokesman Harry Pierre.For constitutional amendments, sponsors must gather the required signatures this fall. Then, their proposals would have to be approved by at least 25 percent of the Legislature in 2008 and again in 2009-2010 to appear on the 2010 ballot.The 13 certified petitions cover nine different topics. Of these, 10 are proposed laws and three constitutional amendments.”It’s still very early in the process,” said state Rep. Steve Walsh, a Lynn Democrat. “We would not see them unless they get the required number of signatures.”Walsh said some of the initiatives have been tried previously. “The move to decriminalize marijuana has been around for some years. Some people are for it and others still feel it’s a gateway to bigger problems,” he said.Coakley explained that the certification process by her office does not imply support or opposition, “but that simply the constitutional requirements were met for these initiatives to obtain further signatures.”