Webster Financial Corp. will move into at least 14 branches that Citigroup Inc. is closing next month, marking the Connecticut bank's most aggressive push into the Boston area since it opened an office downtown in 2009.
Webster, which has about $24 billion in assets, is set to announce on Friday that it will take over Citi's leases and reopen the offices under its name in mid-January.
Webster officials declined to comment on the terms of the deal, but they said the bank expects to spend millions of dollars a year to expand further in Boston. Citi, the New York financial services giant, is not selling its loans and deposits as part of the transaction, meaning that Webster will have to lure customers away from other banks in the market.
James C. Smith, the chief executive, said that Webster, headquartered in Waterbury, Conn., bills itself as a regional institution, and moving into the Boston area was always part of its long-term plan. In Boston, Webster has primarily focused on commercial and private banking from its offices in the former Boston Stock Exchange on Franklin Street.
Webster will gain branches in Copley Square, Kendall Square, the South End, Lexington, Burlington, Newton, Wellesley, and other locations.
"This gives us immediate critical mass in the market," Smith said. "Boston is critically important to us. It completes us."
The Boston market, with its booming economy and growing population, is an attractive one for regional banks, according to analysts. And Webster is getting spaces in prominent locations that are already built for banking.
"If it's not a home run, it's a good solid triple for them," said Suzanne Moot, a Milton banking consultant.
But with 300 separate financial institutions in the area — from national giants to small mutual banks and credit unions — Webster will face challenges in attracting new customers, Moot said.
"If what you want is the checking account and also the savings account and the household relationship, that is a goal that takes time to achieve," Moot said. "People don't change primary relationships very often."
In September, Citi announced that it was going to close its 17 retail branches in the Boston area and instead focus on its core markets of Los Angeles, Miami, New York, and San Francisco. Webster is still negotiating to take over the leases on the three remaining Citi branches.
"We are pleased to have come to an agreement with Webster Bank," said Andrew Brent, a spokesman for Citi. Citi plans to maintain its private banking office for wealthy customers and continue to serve institutional and commercial banking clients here.
With the Citi leases, Webster will have 34 branches in Massachusetts. The bank has 163 offices in Connecticut, Rhode Island, New York, and Massachusetts.
Webster has extended employment offers to the about 80 Citi workers at the local branches.
Deirdre Fernandes can be reached
at deirdre.fernandes@globe.com. Follow her on Twitter @fernandesglobe.