A casino proposal for Suffolk Downs should be considered by all of Boston in a citywide referendum, Suffolk District Attorney Daniel Conley, a candidate for Boston mayor, said Monday in a major departure from the policy of Mayor Thomas M. Menino.

“We’re one city; we have one shared future,” Conley said in a Globe interview. “This referendum must be citywide and the results must be read to reflect our shared stake in the outcome of this important vote.”

Menino favors limiting the casino vote to the East Boston neighborhood around the horse track. In publicly breaking from the mayor on the high-profile casino issue, Conley distinguished himself in a crowded pack of mayoral contenders, at the risk of alienating Menino, who remains a powerful political force.

Under the 2011 state gambling law, no casino proposal can be considered for a license unless it wins the endorsement of the host community in a referendum. The law allows the state’s largest cities to limit the vote to the ward in which the project would be built — or to expand the vote citywide.

Menino, who is not running for reelection, has been adamant that the effects of a Suffolk Downs casino would primarily be felt in East Boston, so only those residents deserve a vote on the plan. His spokeswoman, Dot Joyce, reinforced his position Monday: “The city of Boston will continue to follow the letter of the law which says that in cities [our] size the vote should be in the neighborhood that is impacted,” she said by e-mail.

Suffolk Downs, with its partner Caesars Entertainment, has proposed a $1 billion gambling resort at the track.

Conley agreed that East Boston “would feel the greatest impact” of the Suffolk Downs project, but argued that “a casino is going to affect all of us. . . . I think it’s going to affect city services in a significant way; it’s going to impact our tax revenue.”

Conley’s position on a citywide vote would appear to have broad support: 66 percent of Boston adults favored a citywide vote, while 27 percent believed East Boston alone should make the decision, according to a Globe poll conducted in March by the Survey Center at the University of New Hampshire. The margin of error was 4.7 percent.

Calling himself a “casino agnostic” lacking strong feelings either way, Conley said no casino should be built at Suffolk Downs unless the project is approved by a majority of all city voters — as well as a majority within East Boston.

“Essentially, that would give the people of the host neighborhood a position of primacy and an important protection from having a casino imposed on them, but in a two-part threshold, it prevents just a single neighborhood from setting a course for the entire city,” he said.

If the referendum were to fail, Conley said he is “ready to pursue a broader vision” for the neighborhood, citing the transformation of the South Boston waterfront after a proposal for an NFL stadium failed.

“Instead of one project, a stadium, the city has created tens of thousands of jobs across a decade and it’s still going,” he said. “Now it’s referred to as the Innovation District. . . . Maybe that’s what the area over in East Boston ought to be? I think there are many things we could do over there with some imagination and some partnership and some planning.”

After Conley’s announcement, the Globe asked other prominent mayoral candidates to take a position on the casino referendum.

John Barros, a former School Committee member, agreed the vote should be citywide. “While there can be an economic benefit, there will also be social detriment,” Barros said in a statement. “Which is why it is my belief that the voters of Boston, as the legislation provides, should be provided an opportunity to fully review and vote on the issue.”

Bill Walczak, a longtime community organizer, also called for a citywide vote: “We need to listen to our citizens on a decision that has a potential lasting impact on our city, and we need to make sure every voter has a chance to weigh in.”

Several candidates reached Monday night disagreed.

Councilor Felix Arroyo said he supports “a local vote on the casino because I believe those most impacted by the development should be the ones to decide this issue.”

Councilor Rob Consalvo “believes the neighborhood should decide,” his campaign said. “He has long supported an East Boston-only referendum.”

Councilor John Connolly, through a spokesperson, said big development projects disproportionately affect local neighbors, who should be the ones to decide if the project moves ahead.

Councilor Michael Ross also said East Boston should have the vote: “I believe that our neighbors, families, and businesses in East Boston . . . should have their voices heard the loudest.”

A Suffolk Downs spokesman declined to comment on Conley’s call for a citywide vote.