Lady Lake, Fla. ? He’s been the most aggressive presidential candidate in Florida so far, and he’s got to be.

Three out of four voters don’t know Mitt Romney, and only 6 percent favor him over better-known rivals like John McCain and Rudy Giuliani, according to a recent Quinnipiac University poll.

But by racing to be the first presidential candidate of either party to make a public splash in Florida, Romney sent a message to the nation’s largest battleground state.

“It’s hard to imagine a Republican being president without carrying Florida,” he told reporters Friday night after addressing a standing-room-only crowd at The Villages, a sprawling retirement community in central Florida.

Romney charmed many seniors with his energetic speaking style, professed love for his “sweetheart” wife of 37 years, and conservative philosophy touting smaller government. He showed poise when a heckler attacked him for being a Mormon: “You sir, you are a pretender. You do not know the Lord.”

The audience booed the heckler.

“One of the great things about this land is that we have people of different faiths and different religions, but we need to have a person of faith lead the country,” he said, as the audience gave him a standing ovation.

The incident reinforced the hurdle a little-known candidate from a little-understood religious background faces in winning over the Christian conservatives who can sway GOP primaries.

Romney, McCain and Sen. Sam Brownback of Kansas were slated to attend an Orlando convention of the National Religious Broadcasters this weekend. McCain will also make a public appearance at a Vero Beach church today.

The presidential race in Florida has gotten off to its earliest start ever as lawmakers prepare to move up the primary from the second Tuesday in March to the last Tuesday in January. Florida could be the first southern state to go to the polls, just one week after New Hampshire.