The Pittsburgh Public Schools yesterday said it would modify class times at several schools and provide yellow-bus service to an additional 4,100 students if a Port Authority work stoppage occurs next month.

Classes at the Gifted Center in the West End would be suspended, but all schools would remain open, according to information the district mailed to parents and posted on its Web site at www.pps.k12.pa.us.

The district would implement an earlier schedule -- 6:30 a.m. to 1:30 p.m. -- at Carrick High School; Peabody High School, East Liberty; Schenley High School, Shadyside; the High School for the Creative and Performing Arts, Downtown; and the university-partnership school, Hill District.

It also would implement the earlier schedule for middle-grade and high-school students at the Student Achievement Center, Homewood, and for ninth-graders at the Frick building, Oakland.

All other students in early-childhood programs through 12th grade -- including Frick students in grades six through eight -- would keep their regular class times.

The staggered start times would give the district's 11 bus carriers time to provide yellow-bus service to more than 4,100 students who usually use district-issued Port Authority bus passes to get to and from school. That figure includes about 3,400 district students and about 700 students at nonpublic or charter schools, district spokeswoman Ebony Pugh said.

Within seven days, she said, those students will receive letters notifying them of yellow-bus pickup and drop-off times.

The financially strapped district spends more than $200,000 a month on Port Authority passes. If a work stoppage occurs, Ms. Pugh said, the district will look for a refund.

Even with the staggered start times, carriers would have to put extra buses on the road to accommodate all of the additional riders. "We will incur costs; at this time, we don't know how much," Ms. Pugh said.

On Dec. 1, the Port Authority plans to impose a new contract on workers, raising the specter of a strike or lockout. Negotiations began more than a year ago, and the workers' last contract expired July 1.

If a work stoppage occurs, the district will alert parents by phone, with a bulletin on its Web site and through the news media. Ms. Pugh said a work stoppage also could prompt some nonpublic or charter schools to modify their schedules.

The district said it didn't anticipate immediate changes to after-school or athletic activities, and it plans to continue serving breakfast at all schools.

But Ms. Pugh said classes at the Gifted Center would be suspended because the district can't spare the buses needed to transport elementary pupils to and from their home schools.

Instead of going to the center one day a week, she said, gifted students in kindergarten through eighth grade would receive gifted instruction in their home schools. Teachers from the Gifted Center would be sent to the home schools.

Special-education students in the Community Based Vocational Education and Start on Success programs would temporarily lose community placements. They would receive instruction in their home schools until alternative transportation could be arranged, Ms. Pugh said.