WASHINGTON — Supporters of a third-party presidential bid by Mayor Bloomberg launched a 50-state petition drive yesterday seeking to “draft” the billionaire who is edging closer to entering the race while continuing to deny he is a candidate.

The petition effort was announced by two veteran political hands who say the current system in Washington is broken and needs a nonpartisan, pragmatic leader like Mr. Bloomberg.

A former spokesman for President Jimmy Carter, Gerald Rafshoon, and a longtime Republican consultant, Doug Bailey, are not the first to launch an online petition drive for the mayor, but their move comes at the height of primary campaign season.

The two filed papers with the Federal Election Commission and the IRS to start the draft Bloomberg effort. “He’d be a very unique candidate for a very unique time,” Mr. Rafshoon said.

Mr. Bloomberg continues to maintain that he is not a candidate, but has quietly been polling and conducting a sophisticated voter analysis in every state as he decides whether to launch a presidential bid.

In New York, the mayor demurred yesterday when asked about the new appeal.

“It’s very flattering but I am not a candidate for president of the United States. I’ve got a job which I think is a phenomenal job,” he said.