The job requires the toughness of a traffic cop, the warmth of a den mother and tact of a diplomat. On January 5, the first day of the 2011 legislative session, it will belong to Rep. J. Brendan Sharkey, D-Hamden.

Sharkey, 48, a five-term legislator best-known as an advocate of “smart growth” and regionalism, becomes House majority leader on a day when the spotlight will be on Dan Malloy, who takes the oath as governor.

For the first time in 20 years, the governor will be of the same party as the House majority, meaning that Sharkey will have advantages and burdens not faced by his immediate predecessors.

“You can’t compare the job of majority leader today with what it was last year or five years ago or 10 years ago. Instead of playing defense, you’re playing offense,” said Rep. Michael P. Lawlor, D-East Haven, one of the senior lawmakers.

It will fall to Sharkey keep the legislature’s largest and most diverse caucus unified as Malloy undertakes the challenge of trying to restructure government and erase a $3.3 billion deficit.

“That’s always a challenge,” Sharkey said. “We are such a big tent, and we have so much diversity.”

Even with the recent loss of 14 seats, the Democrats still will hold 100 of the 151 House seats — barring vacancies caused by legislators who might resign and join the Malloy administration.

“I feel as though that’s my job, to make sure we hang together,” Sharkey said. “The majority leader needs to ensure that all the voices within the caucus are heard and participating and part of a team.”

It sounds easy. Lawlor likens it to herding cats.

“It certainly is an imperfect science,” Sharkey said. “It can’t be completely mastered.”

House Majority Leader Denise Merrill, D-Mansfield, who is leaving the legislature to become secretary of the state in January, said some caucus members will find their loyalties tested, especially if Malloy’s restructuring plans run afoul of Democratic constituencies.

“The majority leader is going to try to navigate all that,” Merrill said. “There will be different alliances forming all over the place.”

Another new factor will be a more robust Republican minority. Holding only 37 seats for the past two years, the GOP caucus was too small to attempt coalitions on any issues with conservative and moderate Democrats.

With 50 seats, the Republicans can try to block legislation by drawing 26 of the 100 Democrats to their side on any issue. From the late 1980s to the mid-1990s, when Republicans held 60 or more seats, a moderate Democratic caucus often acted as a swing vote, particularly on fiscal issues.

“To the extent folks feel they are not being heard, it enables those fault lines to become chasms,” Sharkey said. “My job as majority leader is to prevent that from happening.”

Sharkey was narrowly chosen as majority leader over a more liberal legislator, Rep. Andrew Fleischmann of West Hartford. But Merrill said she sees Sharkey as ideologically in tune with the majority, which is liberal.

“I think he basically has very progressive instincts. Regionalism, I consider that a progressive vision,” Merrill said.

But Sharkey was among a minority of Democrats who sided with the business community in 2009 by voting against a bill requiring businesses to provide paid sick days. No other state has such a law, and opponents said it would add to the perception of Connecticut as hostile to business.

And he was among the House Democrats who agitated during the last session for the majority to better communicate an understanding of the state’s fiscal crisis and a willingness to make spending cuts.

“The message is critical,” Sharkey told The Mirror in late February. “If you say we can get out of it without draconian cuts, you are whistling past the graveyard.”

The quote caused some momentary friction between Sharkey and the top leader in the chamber, House Speaker Christopher G. Donovan, D-Meriden, who had been resisting deep cuts.

But two days later, Donovan publicly backed recommendations made by a Sharkey-led task force to reduce costs through regionalism and efficiencies. Donovan had named Sharkey, a former chief administrative officer in Hamden, to lead the group in January.

Sharkey said his relationship with Donovan is solid, forged when they were part of a group that was effectively exiled for a time after backing the loser in a leadership fight.

“That’s where Chris and I forged our relationship and our friendship. That’s a relationship that’s endured over the years,” Sharkey said. “We can talk honestly with each other, and we don’t have to pull punches.”

It was Donovan who named Sharkey as the co-chairman of the planning and development committee after becoming speaker.

With his own background in municipal government, Sharkey has backed better funding for towns. He was one of 46 Democratic legislators who proposed raising the hotel tax this year to provide $20 million to help fund regional initiatives that could save municipalities money.

He is a graduate of Georgetown University and the University of Connecticut Law School. He owns a consulting business, AmeriZone, which expedites obtaining building permits nationally. He said most of the company’s business is out of state.

Sen. Edward Meyer, D-Guilford, the co-chairman of the environment committee, accused Sharkey of a potential conflict of interest this year when Sharkey let die a bill that would have transferred the approval of telecom tower sites from a state siting council to the towns.

Sharkey said he had not had a telecom client in more than five years. Meyer congratulated him after he won the race for majority leader.

“He was very gracious,” Sharkey said.

Rep. Robert Godfrey, D-Danbury, a deputy speaker and one of the few Democrats who has served under a Democratic governor–the last, William A. O’Neill, left office in 1991–said Sharkey will be the only new legislative leader, but all the leadership roles will change under a new governor.

“It’s going to be an interesting dynamic,” Godfrey said.

Donovan and Senate President Pro Tem Donald E. Williams Jr., D-Brooklyn, no longer will be the top Democrats in the building. Instead of reacting as opposition leaders to a Republican governor, they will have to define a partnership with a Democrat.

With the departure of Gov. M. Jodi Rell, House Minority Leader Lawrence F. Cafero Jr., R-Norwalk, and Senate Minority Leader John McKinney, R-Fairfield, become the highest-ranking Republican office holders in the state.

On both sides of the aisle, the legislative leaders say they expect Malloy to be a more activist governor than Rell and more engaged with the legislature.

“We are excited about the prospect of a governor who is engaged,” Sharkey said.