Mayor Bloomberg today will move to reopen contract negotiations with the city teachers union, a move sure to ignite a full-scale battle between Mr. Bloomberg and the union’s powerful president, Randi Weingarten.

What the administration will ask Ms. Weingarten to do would be unprecedented, a top official said: It wants to have the authority to remove teachers from the city payroll if they remain in the system, but without an actual job, for 12 months.

The push comes in response to a recommendation being released today in a report by a national nonprofit, the New Teacher Project. The report describes a situation it says is “untenable.”

Under a contract negotiated in 2005, teachers who have been removed from their schools, or “excessed,” remain on the city payroll but are not guaranteed a new job placement. According to the new report, that provision has created a group of more than 600 teachers, known as the “Absent Teacher Reserve,” who are receiving regular salary payments and health benefits without actually teaching in a classroom — at a cost projected to reach $81 million by the end of the school year.

The report calls the costs “staggering,” noting they will only snowball over time if no change is made.

Indeed, both the city teachers union and the Department of Education say the escalating cost presented by the unplaced teachers is a serious problem that must be resolved. What the two sides dispute is how to solve it.

While the union has suggested the Department of Education make efforts on its own to place teachers who do not have jobs, the city has staunchly opposed that.

The new hiring process was meant to introduce “open market” principles to a system that had been in many ways centrally directed. Before, principals were forced to accept teachers handed to them by the central administration, and novice teachers were bumped from jobs by any senior teachers who wanted them. The new process gives principals more freedom, letting them interview candidates and review resumes to make their decisions.

School officials say that any return to such centralized personnel directives would eliminate important progress that has helped principals and teachers negotiate better matches.

In an interview yesterday, the city Department of Education’s director of labor policy, Daniel Weisberg, said that returning to such a system would be a “tragedy.”

Meanwhile, the union has stood against the Department of Education’s suggestion that teachers sitting in reserves for a long stretch be fired, an idea that city officials first proposed during contract negotiations in 2005.

The union filed a lawsuit against the city three weeks ago alleging that the new arrangement discriminates against older teachers, who it says are disproportionately left without jobs. Ms. Weingarten has suggested that the Department of Education could save money by using Absent Teacher Reserve teachers to fill vacancies, rather than hiring new teachers.

The New Teacher Project inserted itself into the debate earlier this year, after making an extensive study of the new hiring system.

Drawing on city data it collected, the nonprofit came up with a proposal it felt would cut through the political stalemate: The city should not fire teachers after 12 months of not being placed, but rather put them on an unpaid leave of absence that would end if the teacher found a new job.

The report also disputes the UFT’s characterization that older teachers are being discriminated against, finding that excessed teachers with long experience were as likely to be hired as teachers with little experience.

The New Teacher Project first took its unpaid-leave proposal to the UFT five months ago, and then served as a mediator in negotiations between the union and the Department of Education to discuss the idea, its president, Timothy Daly, said yesterday.

But Mr. Daly said that when talks ended with only the Department of Education signing on and the union refusing, the New Teacher Project decided to take its findings public. He said the decision was a “last resort.”

“Our feeling is that this is an issue that affects everybody that sends their child to a New York City public school, and it affects everybody who works in New York City public school,” Mr. Daly said. “It was important to make those facts public.”

The city is already rushing to show its support for The New Teacher Project idea, but the UFT is as quickly opposing it.

In a conference call with reporters yesterday afternoon, Ms. Weingarten dismissed the report as “slanted and ill-considered and factually inaccurate.”

She also described the idea as “terrible education policy,” saying it would create a disincentive to work at a struggling school at risk of being shut down, an outcome that leaves teachers excessed to the Absent Teacher Reserve. “It basically says, don’t come to schools that have challenging students, because if a school closes, you will be fired,” Ms. Weingarten said.

She invited four teachers who were excessed from their jobs at the old Evander Childs High School, a large complex that is being shut down and replaced by new small schools, to come to the UFT and speak to reporters in a late-afternoon conference call. All four of the teachers said they desperately want to work but have not been able to find jobs. They said they suspect their age is a factor.

“It’s an insult,” a 21-year veteran social studies teacher, Michael Miller, said. “We want to work. We want to teach.”

Once in the Absent Teacher Reserve, teachers serve as substitute teachers. The teachers participating in the UFT conference call said that when they have no substitute jobs they trek to hotels to attend city-run job fairs or sit in the library of their old school building, applying to jobs online and chatting about teaching.

Mr. Daly said he thinks eventually the stalemate will end and his group’s proposal will be implemented.

He said that the New Teacher Project supports a proposal by the UFT to end a financial situation that gives principals an incentive to hire novice teachers over senior teachers by making senior teachers more expensive.

He said he believes the union will ultimately also give in to his group’s proposal.

“At the end of the day, the UFT gets angry at these things, but I think they want what’s best for the profession,” he said.