With 70,000 extra seats, the Philadelphia School District will rid itself of up to 50 buildings in the next three years, officials said Thursday night.

And while it will continue to invest in fixing up its aging buildings, the district will impose a moratorium on construction that creates additional seats.

Closings are not the only option on the table for saving money. Some schools will consolidate. Grade configurations will change at others; the district has 25 different groupings, which will go down to just four.

Officials say their goal is to reduce the district's excess capacity by at least half by 2014.

No schools will be closed in September, but other immediate changes are planned, including some of the grade configurations, the closing of annexes, and the sale of buildings that have already been closed.

The news came at a special, nonvoting meeting of the School Reform Commission at district headquarters.

Though the district faces a $629 million budget gap next fiscal year, this facilities master plan will not fix that, officials said.

"This is a plan that's being driven by educational needs," Superintendent Arlene C. Ackerman said.

Deputy Superintendent Leroy Nunery added that the decisions were "not just about a short-range budget fix."

The district, which has lost 11,000 students in the last five years, enrolls 155,000 students. By 2014, that will be down to 145,000, officials project.

District buildings are about 67 percent occupied. Experts say an 85 percent "utilization rate" is ideal.

Associate Superintendent Penny Nixon said the district would try to keep kindergarten-through-fifth-grade elementary schools at 450 to 600 students, K-8 elementary schools at 450 to 800, middle schools at 600 to 800, and high schools at 1,000 to 1,200.

There will be some exceptions to those guidelines, Nixon said, but she did not outline them.

That seems to mean a turn away from small high schools, which during the last decade were popular in Philadelphia. Ackerman said small schools were "not always fiscally possible."

District secondary schools are particularly under capacity, with a utilization rate of 59 percent, officials said.

Future closings and consolidations will be announced in October, vetted in community meetings, and then voted on by the SRC in January.

Coming in September, however, are new grade configurations at two schools, Ethel Allen and Ellwood. Grades will be added at three current and future Renaissance charter schools: Smedley and Mann Elementaries will get sixth-grade classes, and Gratz High will get middle school classes.

Mastery Charter Schools runs Smedley and Mann, and it will soon take over Gratz. The changes will allow Mastery to have a K-12 continuum in those neighborhoods.

There will also be consolidations at Lamberton, Hancock, and LaBrum Schools. An annex at Elkin School will close, and students at Bridesburg School will temporarily relocate during renovations.

The Ada Lewis, Alcorn Annex, Beeber-Wynnefield Annex, Childs, Gillespie, Walton, and Muhr Schools, all already closed, will be sold.

Officials said they would ask communities to help decide how to reuse closed buildings, and a soon-to-be-introduced "adaptive reuse" plan would give discounts off fair market value if an organization planned to use a building for educational or other public purposes.

Meetings on the changes will be held around the city beginning Tuesday. More information is available at the district's master-plan website, www.philasd.org/fmp