But Brookhaven at Lexington is also the epicenter of Grandmothers for Obama, an enterprising organization of more than 600 women nationwide that is reaching tens of thousands of older voters in swing states this fall with carefully worded, hand-signed, hand-stamped postcards.

“At our age and stage, the telephone’s difficult,” said Margot Lindsay, 87, a Brookhaven resident and grandmother of three who founded the group with one of her neighbors in the Waltham Street complex. “And certainly ringing doorbells is not part of our genes anymore.”

President Obama and Mitt Romney are competing fiercely for the senior citizens vote, which has accounted for about 16 percent of the turnout in recent presidential elections, according to Carroll Doherty, associate director of the Pew Research Center, a nonprofit, nonpartisan institution based in Washington, D.C. In the past two elections, the majority of voters age 65 and older backed Republicans: In 2008, John McCain beat Obama among seniors by a margin of 8 percentage points; in 2004, President George W. Bush beat John Kerry among seniors by 5 percentage points.

But this year a few more seniors might be leaning Democratic.

In a recent Pew poll, 48 percent of likely senior voters said they favored Romney, while 46 percent said they favored Obama. “If Obama can peel off some of Romney’s support in this age group, it certainly would be an important thing for him,” Doherty said.

On a recent Sunday morning, Lindsay and a dozen other leaders of Grandmothers for Obama gathered around a table in Brookhaven to bundle up copies of their most recent postcard, which they designed after watching the Democratic and Republican national conventions.

“What kind of America do you want? The choice is clear,” says the bright yellow card with black type. With Obama, it says, “We’re all in this together.” With Romney: “You’re on your own!”

The women were planning to distribute the bundles to other Grandmothers for Obama chapters, where members would inscribe each card with a handwritten message and a signature. One group leader, Muriel Finegold of Boston, said she generally writes, “For the sake of our children and grandchildren, please join me in voting for Obama.”

“If you write on it, people are more apt to pay attention,” said Finegold, a retired social worker who has been volunteering on campaigns since 1952, when she knocked on doors for Adlai Stevenson.

Elsewhere, other groups of women and senior citizens have formed to support Romney. In April, in response to Democratic strategist Hilary Rosen’s comment on CNN that the GOP candidate’s wife, Ann Romney, had “never worked a day in her life,” the campaign launched Moms for Mitt, a Facebook community that now has more than 90,000 members and hosts vibrant political discussions daily, according to a campaign staff member.

Last week, the campaign announced the formation of Florida Seniors for Romney, a coalition of volunteers who are knocking on doors, making phone calls, and working office shifts. The group’s chairwoman is Betty Ryan Douglas, 78, mother of Republican vice presidential candidate Paul Ryan and a resident of south Florida.

“Florida seniors know that Mitt Romney and my son, Paul Ryan, will protect Medicare for me and my generation, and preserve it for Paul’s and my grandchildren’s generations,” Douglas said in a campaign statement. “Florida seniors know we can’t afford four more years of the last four years and we can’t pass on more Obama debt to our children.”

Luanna Devenis, secretary of the Republican Town Committee in Lexington, said she and other Republican senior citizens in the area are busy campaigning on behalf of both Romney and US Senator Scott Brown. Devenis, 84, and her colleagues on the town committee have been mailing out campaign literature, she said, and she knows older Republicans who plan to stand near the polls with posters on Election Day.

Republicans, she said, “are very much a minority here in Lexington . . .  but it makes us work harder.”