A settlement crafted last week seeking to curb the use of seniority as a factor in teacher layoffs in the Los Angeles school system could become one of the nation's most far-reaching overhauls of the "last hired, first fired" policies common in school districts. If approved by a judge, the settlement would shield up to 45 low-performing schools in the district from the layoff process. It also would cap cuts made in other district schools. It comes in response to a class action against the district, filed in February by the American Civil Liberties Union of Southern California and other groups. That lawsuit alleged that civil rights of students in three schools in impoverished neighborhoods were violated when half or more of the teachers in the schools were let go under the district's layoff procedures, as part of a cost-cutting plan last year. The action in the 678,000-student district, the nation's second-largest, is notable not only for the support it ended up garnering from the city's mayor and ultimately from the district itself, but also because efforts to change layoff policies through legislation have fallen short recently in California and on Capitol Hill. Observers said the settlement could be a model for other districts, though as the basis for future legal action its status is unclear. It also comes at an important time for Los Angeles, which faces a projected deficit of about $270 million next year and more than $800 million by 2012. The city's teachers' union has indicated, however, that it will fight the settlement, saying that it wouldn't alleviate a concentration of inexperienced teachers in struggling schools. The economic crisis also has brought the issue of layoff policy to the forefront of reform debates. Though seniority-based layoffs are common in districts throughout the nation, critics of such policies note that they tend to affect schools serving poor and minority students more because those schools are often staffed by novice teachers who haven't earned tenure. They also tend to drive up class sizes across a district more than other layoff procedures, since more novices must be cut to achieve budget parity.