Progressive Democrats will hold Gracie Mansion, the public advocate and comptroller offices, and likely the City Council speakership in the new year -- for the first time in 20 years -- but odds are there will be fissures among the ideological allies.

Incoming Mayor Bill de Blasio, Public Advocate Letitia James, Comptroller Scott Stringer and the top candidate for City Council speaker, Melissa Mark-Viverito, could eventually clash on fiscal and social issues as well as any questions over the new administration's managerial performance, political experts said.

"You might find the disagreements are going to be over how progressive to be," said Ken Sherrill, Hunter College professor emeritus of political science. "I would not be surprised if what we found fairly quickly was that de Blasio was not as progressive as the majority of the City Council."

City Council members likely will want to spend more than de Blasio does, and one major point of tension for Mark-Viverito -- if she is chosen -- and de Blasio may be noncitizen voting rights, which she supports and he has opposed, Sherrill said.

James and Stringer have said they are bound by their job descriptions to stand up to the mayor when necessary.

"If we're all in lockstep, then we're not really doing our job," Stringer said in an interview. "We've been under Republican rule so long, I think at some level, people think how are all the Democrats going to approach this?"

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Stringer's comptroller tasks include investigating other city offices' finances and effectiveness, including the mayor's. A primary responsibility for James as public advocate is to be a watchdog on behalf of New Yorkers.

"Yes, he is a friend, and yes, he is an ally, but you elected me to be a public advocate and a thorn in his side each and every day," James said of de Blasio at an education rally this month.

She said she'll press de Blasio to fulfill his campaign promises on education in his first 100 days. "We can't rely on the fact that we elected a progressive into City Hall," she said. "We can't become complacent."

Stringer said that though the comptroller and mayor work together on issuing bonds and creating the city's four-year financial plan, the comptroller blows the whistle on fraud or waste.

De Blasio's efforts to help Mark-Viverito secure the council speakership have been widely seen as a play to place a longtime ally in the city's most powerful legislative office. Mark-Viverito this month claimed she had enough votes from colleagues in the 51-member council to be chosen speaker on Jan. 8. Her top opponent in the race, Dan Garodnick, and his backers have countered that he would be more independent of de Blasio as speaker.

"Obviously she is someone who is a friend and early supporter," de Blasio said last week. "If she is the one chosen, I'm convinced we will work well together. It's as simple as that."

Mark-Viverito said she wasn't seeking the job just to carry de Blasio's water.

It's the council's "charter-mandated responsibility" to serve as checks and balances to the mayor, she said in a statement. "I support a robust institution that has the oversight, budgetary and legislative authority to collaborate when possible, but also can take its own initiative when necessary."

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She and other council members, especially new additions to the growing Progressive Caucus, which she co-founded, likely will want to keep discretionary funding -- financing for individual members' districts -- while de Blasio may need to rein in spending. He'll be under more pressure by labor-friendly council members to produce revenue for raises as he negotiates the city's 152 open union contracts.

"While [Mayor Michael] Bloomberg gave him a balanced budget, there's still areas where he'll still have to make some significant cuts and difficult choices," Democratic consultant Basil Smikle said.

Mark-Viverito may also continue to advocate to legalize voting in the city for noncitizens. De Blasio spoke against her bill during the campaign.

Council members based in the outer boroughs may pressure de Blasio to expand the green taxicab services, operating in their districts, despite opposition from the yellow cab industry, which was a big contributor to the mayor-elect's campaign. Progressive members also will want fast action on affordable housing and homeless policy initiatives.

Competing branches of government, not to mention personal ambitions, naturally inspire conflict, whatever the party affiliation or ideology, veteran Democratic consultant Hank Sheinkopf said.

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De Blasio's counterparts in government need "to prove they are doing the job for the people who elected them," he said. "That's always the case."