A new teacher evaluation system that’s likely to become state law could mean that, for the first time, school districts will fire teachers if they repeatedly fail to boost their students’ test scores.

But to do that, the state and school districts will have to track student work in more detail than they ever have before. And state and city teachers union officials sold the idea as a way to create better professional development for teachers and principals.

The agreement struck between the state education department and the teachers union today means that, in three years, all New York teachers will be evaluated according to a new 100-point scale, with 40 of those points determined by student achievement data. The agreement was ushered out just in time for the June 1 second round deadline for the Obama administration’s Race to the Top grant competition.

So far, the new teacher evaluation system exists only in concept. To flesh it out, school districts will have to create a new battery of customized tests or other ways to measure student learning.

If Albany passes the bill, evaluations would begin in two phases. Teachers in tested grades and subjects would start receiving rankings in the 2011-2012 school year, using next year’s test scores as the baseline for measuring growth, State Deputy Education Commissioner John King said today. All teachers will begin receiving the new form of ratings by the 2012-13 school year.

That means that in two years, the state and local school districts would need to use new methods to judge student growth in all subjects and grades, not just those currently tested. The proposed law leaves open several options for the state and district to measure students’ progress — new tests could be developed, or districts could use portfolios of student work or other performance evaluations.

In all cases, new local assessments would have to meet regulations set by State Education Commissioner David Steiner. An advisory committee that includes teachers, principals and superintendents will help Steiner develop the new rules, the proposal states.

Steiner argued today that the expansion of evaluated subjects would help boost the status of subjects like the arts that have historically been marginalized when schools focus resources on improving test scores.

“We feel very strongly that subjects are created equally,” Steiner said. “The fact that we have not yet had any collective effort to create meaningful and good evaluations [in non-tested subjects] has ironically put those subjects and teachers at a severe disadvantage.”

The heads of the city and state teachers unions, who enthusiastically endorsed the plan today, said that the new evaluations will also give teachers better feedback on how they can improve. United Federation of Teachers President Michael Mulgrew said the new four-category scale will allow principals and teachers to target professional development and coaching to areas where they need the most help.

“This now embeds that inside the evaluation process,” Mulgrew said.

Steiner, along with King and the teachers union presidents, urged legislators to pass the new bill by the June 1 deadline for the second round of the federal Race to the Top competition. The Race to the Top scoring rubric sets aside 58 points, the most heavily weighted single category, for how a state judges and improves teacher effectiveness based on their performance.

Both houses received the proposed legislation around 1 p.m. today, and Senate Democratic Conference Leader John Sampson has pledged to move quickly on the bill, union sources said.

Steiner acknowledged that significant work will be needed to launch the new evaluation system, especially as the state education department simultaneously overhauls its testing system, which critics deride as overly simplistic.

“We have an enormous amount of work to do,” Steiner said, “but we cannot be happy with where we are now.”