Mormons who are Democrats are always a lonely bunch, but never more so than in this election year when one of their fellow church members is about to make history and be crowned the Republican nominee for president.

So an increasingly assertive caucus of Mormon Democrats is planning a coming-out party during the Democratic National Convention in Charlotte, N.C. The group, which calls itself “LDS Dems” — LDS for Latter-day Saints – expects to draw about 200 motivated Mormons from around the country at the event, planned for Sept. 4 at a hotel next to the convention arena. Their keynote speaker will be Senator Harry Reid of Nevada, the majority leader and a Mormon who recently accused his co-religionist and the Republican nominee, Mitt Romney, of having paid no taxes for years, without providing any evidence to back up the claim.

Greg Prince, a Mormon businessman and pathology researcher in Washington who is helping to organize the event, said: “It’s not just that Mormon Democrats, particularly in Utah, have been playing defense. They haven’t been playing. Within the State of Utah, they basically conceded the entire active Mormon population to the Republicans.”

Mr. Prince said he donated the maximum to Mr. Romney’s campaign during his last run for president, in 2008, because of his relatively moderate record as the governor of Massachusetts. But Mr. Prince said he became disillusioned as Mr. Romney moved to the right to win the nomination this time. Mr. Prince said he supported a public safety net for the poor and immigration policies that keep families intact – Democratic positions that he said should be a natural fit for Mormons.

A poll by the Pew Research Center released in January found that 74 percent of American Mormons identify as Republican, 17 percent as Democrat, and 9 percent say they are independent or don’t know their preference.

It was Ezra Taft Benson who cemented the Republican Party’s hold on Mormons, church historians say. Mr. Benson was agriculture secretary for eight years under President Dwight D. Eisenhower; a staunch anticommunist and supporter of the right-wing John Birch Society, Mr. Benson later served as president and prophet of the Church of Jesus Christ of Latter-day Saints from 1985 to 1994.

The church says it does not endorse any political party. But its position against gay marriage has kept it in the Republican orbit.

LDS Dems was formed last October in Utah, and has grown to more than 2,000 members, said Matt Lyon, the executive director of the Utah Democratic Party. Only 7 percent of registered voters in Utah are Democrats, Mr. Lyon said, and the goal of LDS Dems is to get to 17 percent. They also plan to open chapters in Mormon-heavy states like Arizona, Colorado, Idaho, Nevada and New Mexico.

They are using an approach not unlike missionary work: convincing Mormons one on one that the Democratic Party better represents their moral and religious ideals, Mr. Lyon said.

But the stigma of being a Democrat in Utah is so strong that the state Democratic chairman, Jim Dabakis, said he recently had this telling encounter: He was in rural Iron County meeting with a small group of Democrats, when a man came up to him after the meeting and mentioned that he was gay. Mr. Dabakis, who is gay himself, said, “That must be tough down here.”

The man said that it was, but not for the obvious reason. “I don’t tell anyone I’m gay,” the man told Mr. Dabakis, “because if I do, they’ll know I’m a Democrat.”