Negotiators for FairPoint Communications and the two unions that went on strike against the company on Oct. 17 return to the bargaining table Sunday, in the first negotiations in more than six weeks in the lingering strike by telephone workers.

The U.S. Mediation and Conciliation Service has summoned the two sides to talks in Washington beginning at 1 p.m. Sunday.

Compromise has proved elusive as the strike, which has lasted three-and-a-half months, creates an uncertain future for both the telecommunications company and more than 1,700 workers in Maine, New Hampshire and Vermont. Union members have maintained picket lines in Waterville, Augusta and other Maine locations. Strikers and supporters picketed and sang Christmas carols at the Winslow home of company president Mike Reed a couple of days before Christmas and picketed a company sponsored forum on health insurance in Augusta in early December.

FairPoint has said it’s willing to negotiate with striking workers but doesn’t want to budge on the employees’ core issues: hiring contractors, changing pension plans and reducing health care benefits.

Workers are especially concerned about FairPoint’s demand that it be allowed to hire contract workers. Workers fear they’ll eventually be replaced by lower-paid, less-qualified contractors.

“All of the pensions and health care in the world isn’t going to be any good if you don’t have a job,” said Pete McLaughlin, chairman of the unions’ bargaining committee.

The company contends it needs flexibility to hire contract workers to deal with peaks and valleys in work — especially in the summer, when the old contract guaranteed at least two weeks of vacation for workers during the busiest time of the year.

The last bargaining session was held Nov. 18 in Boston. It ended with no reports of progress.

“The biggest challenge is there’s no good offramp for either side to compromise,” said Barry Sine, an analyst at Drexel Hamilton, a New York-based brokerage firm, who isn’t involved in the negotiations. “There’s no real avenue without being seen as backing down.”

Both sides agree that FairPoint workers had one of the best contracts in the business. They agree that workers need to give up some of benefits to keep the company competitive.

However, workers who stuck with the company when it filed for bankruptcy after buying Verizon’s land-based telephone assets say the company is asking for too much. The company has yet to reverse net losses posted for every year of operation since the purchase from Verizon in 2007.

Striking workers insist they’re not ready to give in unless the company is willing to meet them partway.

“They won’t break us,” said Mary Beam, a customer service worker from Westbrook.

Workers were dealt a blow last week when the National Labor Relations Board dismissed union complaints that the company had bargained in bad faith and illegally imposed terms of its final offer proposal that froze the pension, required health care contributions for the first time and allowed the hiring of contractors.

The unions have vowed to appeal, but the process will take at least several months, officials say.

FairPoint CEO Paul Sunu said the NLRB ruling showed that the unions’ allegations of bad-faith bargaining were “propaganda.” In a statement, he said it’s time to end “all this spinning.”

For now, customer service complaints are growing, with more than 700 in Vermont alone, as FairPoint relies on replacement workers.

Despite the problems, most investors want Charlotte, N.C.-based FairPoint Communications Inc. to stand up to the union, said Sine, the industry analyst. The company probably can weather some residential customer losses if it focuses on holding on to its big business customers, he added.

“All of the shareholders I’ve spoken to understand that pretty significant adjustments need to be made in benefits,” he said. “As unfortunate as the situation is, they need to hold their ground and get the company on a better footing.”