Public Advocate Bill de Blasio is refusing to go along with the city’s aggressive program for rolling out bike lanes and pedestrian plazas, describing Transportation Commissioner Janette Sadik-Khan as a “radical” for pushing those initiatives so hard.

By comparison, he called himself an “incrementalist” — earning a sharp rebuke from the city’s leading bicycle advocacy group.

“Incrementalism would say we want to make progress, and we have to do it with communities, and we have to be realistic,” de Blasio told The Post.

“It’s very clear that’s not the same approach Janette has.”

When he talked about his “incrementalism” at a recent meeting attended by members of Transportation Alternatives, the group’s executive director, Paul Steely White, fired back with both barrels blazing.

“Bill is a good guy, a neighbor of mine and, until recently, a livable-streets stalwart,” White wrote in TA’s quarterly magazine.

“So what happened? When did the tide change? I can’t say for sure, and I’m not convinced it truly has, but I do know there are some well-connected, deep-pocketed people in this city who have an outdated view of our streets — and all the mayoral candidates on speed-dial.”

An advocate accusing de Blasio — a standard-bearer of the progressive movement — of selling out to the rich and powerful doesn’t happen every day.

White told The Post that all the mayoral candidates are “hedging” when it comes to committing to safer streets, not just de Blasio.

“I’ve known Bill for some time as my council member and public advocate,” White said. “Perhaps I do hold him to a higher standard.”

De Blasio, who has been moving to the political center in preparation for his mayoral run, has generally been supportive of TA’s agenda. In his own Park Slope community, he backed Sadik-Khan’s installation of a bike path along Prospect Park West even when some influential residents objected and sued to block it.

But he said he’d stop short of pushing through bike routes without local input, as happened on Kent Avenue in Williamsburg before the plans were restructured.

“There’s a radical tendency: Here’s our plan, and we’re going to move it come hell or high water,” de Blasio said.

He recalled the now-controversial meeting attended by many TA members as friendly and said he was surprised by the backlash.

“I thought there was a very positive dialogue going on at that event,” he said. “I thought my comments were very well received.”

One political source said TA’s run-in with de Blasio indicates it needs to rethink its hard-line strategy.

“If they can’t figure out how to work with a guy like de Blasio, they have a problem,” the source said.

DOT spokesman Seth Solomonow responded, “I know I wouldn’t want to tell the family of someone who died in a crash that we could have saved them but waited on changes because we take an “incremental” approach.

“In fact, there is intense public demand for these projects. We’ve gotten extensive public involvement for Select Bus Service among some two thousand public meetings held each year. For bike share alone we’ve held more than 300 meetings and received tens of thousands of station suggestions, perhaps the largest public outreach ever done for a single transportation project in the entire country, and we continue to work with dozens of elected officials across the city on a range of projects. We have not heard from him on any project, nor as we reached record low safety levels in each of the last five years.”