When President Barack Obama presumably strides onto a North Carolina convention hall stage next September to accept the 2012 Democratic nomination for president, Massachusetts voters and elected officials will be in the midst of calculating election night fallout after a change to the state’s 2012 primary date set up a direct conflict with the Democratic National Convention.

Gov. Deval Patrick this month signed a law, tucked into a mid-year spending bill, which changed the date of the primary from Tuesday, Sept. 18 to Thursday, Sept. 6. Secretary of State William Galvin recommended the change and the Legislature approved it in order to avoid a conflict with the Jewish holiday Rosh Hashanah.

Unacknowledged by anyone at the time, however, was another fact: the newly scheduled primary election coincides with the last night of the Democratic National Convention when Obama will deliver his acceptance speech, potentially forcing hundreds of Bay State delegates to choose between the convention and elections back home.

“It was brought to our attention after the fact,” Galvin told the News Service. “Even (Democratic Party Chairman) John Walsh did not recognize it as such, in part because this is the latest Democratic National Convention in recent memory.”

Galvin seemed reluctant to change the date again, detailing his rationale for choosing Sept. 6 over other available dates, and suggesting the national nominating convention was little more than a formality.

“In a situation like this where we presume it’s a renomination of the president and vice president, it is more a festive event than a political event, so we’re talking about overlapping with a balloon drop,” Galvin said. “We were concerned and are concerned about giving the maximum amount of time for the printing of absentee ballots.”

Gov. Patrick may not feel the same way. The governor, who spoke at the 2008 convention in Denver and has been tapped by Obama’s re-election team to help promote the president around the country during this cycle, would prefer to avoid the overlap with the convention in Charlotte.

A top aide to Gov. Patrick said his office was still reviewing whether another change to the election date would be preferable, and Galvin said he would not rule out another alteration to the schedule.

“I’m open to discussion. But the discussion has to be based in facts and solutions to problems,” Galvin said. “I’m not saying the sixth is the only solution, but I think it’s the best solution.”

Massachusetts typically sends a contingent of 147 delegates to the Democratic nominating convention, including all members of Congress and members of the legislative leadership who are ex-officio delegates. The state Democratic Party said the national convention would normally create a travelling party from the state of 300 to 400 people, a contingent that next year may have to grapple with the ramifications of being away from home on election week, or skipping the national festivities and political networking opportunities.

Galvin, however, said the printing of ballots should hold weight over inconveniencing a few hundred convention-goers, and suggested that any politician involved in a competitive primary would likely forego the trip anyway. He also said the president’s speech will be televised after the polls close for West Coast viewers eliminating a possible to deterrent to voting.

“In planning for this, there will definitely be people who would like to be there that won’t be able to because they are focused on the primary election here,” said Walsh, who admitted to not recognizing the conflict until after the date had been changed.

“I honestly have some concerns, but even if the primary were two days before the speech or a week before or a week after, in any case it’s not the optimal situation,” Walsh said.

In explaining his decision to move the date of the primary election almost two weeks earlier, Galvin cited concerns about having ballots printed as early as possible with a cushion for potential recounts or unforeseen developments. In 2008, Middlesex Register of Probate John Buonomo withdrew his name from nomination after the winning the primary election while fighting charges that he had robbed a courthouse safe, delaying the printing of ballots.

Galvin said moving to August should be out of the question, citing the end of summer vacations, the Republican National Convention and the lack of availability of schools as polling locations as reasons.

Moving the election to Tuesday, Sept. 4 on the first day of the Democratic National Convention, would require cities and towns to pay poll workers overtime to set up on Labor Day, according to Galvin.

Galvin also said he considered the 11th and the 13th, but fell back on his interest in getting ballots printed early so they could be made available to absentee, overseas and military voters in plenty of time before the Nov. 6 general election.

“The governor is already concerned about it. I’m less concerned, to be candid,” Galvin said about the overlap with the DNC. “We shouldn’t lose track of the fact that the main event is the general election.”

State statute mandates that the primary election be set at least seven weeks before the general election, while the federal MOVE Act requires that absentee ballots be sent out 45 days in advance. Massachusetts in 2010 sought a waiver from the MOVE Act, but Galvin said Republican criticism of states that used waivers as “hostile to military overseas voters” is wrong.

“Nothing could be further from the truth,” Galvin said, noting that Massachusetts for the first time this year will email ballots to overseas voters, though the ballots must still be returned by mail.

Walsh said he was not fully aware of the all the reasons that went into selecting Sept. 6 over other dates for the primary, and acknowledged that the current date could be “the best of a bunch of bad alternatives,” but he said if there were other options it would be preferable to move the date. He said he wasn’t sure if forced to choose whether he would remain in Massachusetts on election night, or attend the president’s nomination speech.

“If someone said, ‘John, what would you do?’ I would move it,” Walsh said.