By Saundra Amrhein

ST. PETERSBURG, Florida (Reuters) - Former Florida Governor Charlie Crist made his latest political party switch official on Thursday: He's now a registered Democrat.

Crist filed his party paperwork in his hometown of St. Petersburg, Florida, where in 2010 he announced he was leaving the Republican Party after polls showed he likely would lose its nomination for U.S. Senate to Marco Rubio.

Crist, who was governor from 2007 to 2011, ran as an independent, and Rubio won a three-way race handily.

Crist endorsed Republican presidential nominee John McCain in 2008 but threw his support behind Democratic President Barack Obama in the 2012 White House race.

The former Florida governor announced his plans to formally join the Democratic Party on Twitter last week, tweeting from a holiday party at the White House: "Proud and honored to join the Democratic Party in the Home of the President@Barack Obama!"

On Thursday, Crist shook hands with local residents as he headed into the elections office and granted employees' requests to have their pictures taken with him after he submitted his registration form.

"Do you know what I call you three? Charlie's angels," he said, his arms around three women as they posed for a photo.

Outside the office, Crist told reporters he was "happy to be a Democrat."

"It's very important we all are comfortable where we are, and I can't tell you how comfortable I am as a Democrat," he said.

Crist is expected to make another bid for governor, but he did not commit on Thursday to challenging current Republican Governor Rick Scott in the next election.

Asked whether the party switch was a step toward running for office again, he said, "I really haven't made any decisions about that at this time."

He said he had become disillusioned with Scott over the failures to secure high-speed rail in the state and decisions made about the environment and education funding.

(Reporting by Saundra Amrhein; Writing by Colleen Jenkins; Editing by Paul Thomasch and Paul Simao)