The state said Monday it would step in and attempt to break the stalemate over a new teachers’ contract in Boston, an unusual development that could finally end the acrimonious negotiations that have stalled a new teacher evaluation system.

The move represents a victory for Mayor Thomas M. Menino, who this month asked the state Department of Labor Relations to investigate and propose a resolution, over the protests of the teachers union. Menino has grown increasingly frustrated with the pace of the talks, charging that union officials have been employing delay tactics to prevent a resolution after more than two years of talks.

A key stumbling block has been creating an evaluation system to comply with changes in state regulations last year that call for making student test scores a central part of a teacher’s job review and also speed up the timeline for dismissing unsatisfactory teachers. The city must implement a new evaluation system for this school year or it could run the risk of losing millions of dollars in federal aid aimed at overhauling public education.

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“This is a great step forward for the educational process of our young people,” said Dot Joyce, the mayor’s spokeswoman. “This will move us a step closer to having a teacher-evaluation system that works not just for kids in the classrooms but for the teachers as well.”

Richard Stutman, the teachers union president, said he was disappointed by the decision to order the negotiations into a process known officially as fact-finding. Stutman, who has been involved with Boston teacher-contract negotiations for more than 30 years, said he could not recall another time when fact-finding was ordered to end a stalemate over a Boston teachers contract.

“It is what it is, and we will follow the law,” Stutman said.

The decision came as the city’s 5,000 or so teachers, guidance counselors, and other educators are about to start their third school year without a contract.

Besides teacher evaluations, another sticking point has been wages over the course of the six-year contract. The city is pushing for no pay raise the first year, a 1 percent increase the second year, a 2 percent increase the third year, and a 3 percent increase for each of the final three years of the contract.

The union’s proposal differs only in the first two years. It wants a 1 percent increase the first year and a 2 percent increase the next.

This is the second time the state Department of Labor Relations has intervened in the talks. This spring, after negotiations officially broke down and the two sides declared in impasse, the state appointed a mediator, who has the power only to foster a dialogue and cannot propose any resolutions.

Erica Crystal, the state’s labor relations director, notified both sides about her decision on fact finding by letter. She offered little insight into her decision, saying only that her agency “finds that mediation has failed to resolve the impasse.”

The letter, obtained by the Globe, provides a list of seven potential fact-finders for each party’s review. Each side can eliminate up to three from the list and then must rank the remaining four. From there, the state will decide on a fact-finder.

The fact-finding process can take as little as one month or could last for several months. The resolution recommended by the fact-finder is nonbinding. But if the two sides do not agree to it, then the proposal becomes public within 10 days.

A recommendation from a perceived neutral party could carry considerable weight in the arena of public opinion, putting the disagreeing party in a difficult position in holding out. The talks have grown increasingly contentious this summer.

In a major concession in July, Superintendent Carol R. Johnson pulled a proposal to add 45 minutes a day to most city schools because she said the union was demanding too much money to pay teachers. Union officials had requested the same hourly rate for the extra time, but school officials said the city could not afford that and offered significantly less.

That concession did not lead to a deal, and the episode has since come to highlight just how badly the talks have gone, as rhetoric has occasionally devolved into personal attacks.

Menino, in making his request for fact-finding, accused Stutman of misleading him and other city officials by implying in private meetings that a contract resolution was imminent if the two sides were able to push past the stalemate over lengthening the school day.

Instead, the mayor has said the talks have merely moved from one impasse to another, as the union tries to resurrect issues the city believed had long been resolved.

Stutman, in turn, has accused City Hall of taking control of the negotiations, having lost faith in Johnson’s leadership — an accusation quickly rebutted by City Hall. He also knocked Johnson for attending a back-to-school event at Target last week, characterizing her as being a “glad-hander” instead of attending what became the last day of mediation.

On Monday, just hours before the state made its decision on fact-finding, the union launched another salvo, announcing that it had filed an unfair labor practice complaint with the state. The complaint charges that the School Department has attempted to thwart mediation by refusing to meet face-to-face and by providing the mediator with false information.

“If the School Department is serious about trying to finalize a contract, then they should come back to the table with real proposals and end their media campaign of villainizing the hard-working teachers within the Boston public schools,” Stutman said.

Matthew Wilder, a School Department spokesman, denied the allegations and took issue with the notion that the city was villainizing teachers, saying, “There is no one who respects teachers more than the superintendent of schools, and that’s a fact.”

Myriam Ortiz, executive director of the nonprofit Boston Parent Organizing Network, said that parents have become frustrated with the stalemate and some of the union’s tactics.

“Parents are sick and tired of this,” Ortiz said. “They are completely frustrated with this process. They want the contract signed. They want the district to go ahead and implement the teacher evaluation process they have trained hundreds of people on.”