The shortage of school bus drivers in Fairfax County is so severe that school officials say they will have to change the starting times at 31 schools this fall unless the hiring situation improves significantly, a decision that has upset many parents.

Classes would start later at 17 elementary schools, two middle schools and one alternative center, meaning that some elementary schools would open as late as 9:15 a.m. and release students at 3:50 p.m. Nine elementary and two middle schools would get earlier start times.

Parents at schools being put on a later schedule are especially concerned about the plan, saying that their children will get home too late in the afternoon to do their homework or get to after-school activities. Parents who wait for their children's morning buses to arrive before they leave for their jobs are worried that the later starting times will cause them to be late to work.

But school officials say that given the shortage of bus drivers, their only option is to make school schedules more staggered so that the same drivers will have time to make more runs.

In Fairfax, as in many other Washington area school districts, the region's strong economy and low unemployment rate have made it hard to find workers who will take the seasonal, part-time jobs. Fairfax officials say they are short at least 100 drivers every day and expect to lose even more over the summer. They said it's possible that even more schools will have their schedules changed in the fall if summer hiring is slower than anticipated.

"This is not a situation we want to be in, but we have no choice," Superintendent Daniel A. Domenech said. "This is not even the worst-case scenario."

Officials in other area districts said their driver shortages so far have not forced them to consider changes in school schedules.

Fairfax officials said they decided which schools would get changes in bell times based on how they fit into the entire network of bus routes for elementary, middle and high schools. The biggest change would be at Hybla Valley Elementary, where classes would start at 9:10 a.m. instead of 8:10 a.m.

"It is very hard for parents who work," said Misbah Javaid, who will have a first-grader and a fourth-grader at Hybla Valley in the fall. "There will be a lot of children who will have to stay home unsupervised for an hour. . . . I have seen some children standing out on the street near the school as early as 7 a.m."

At Westbriar Elementary, parents had lobbied for an earlier start time. Instead, school officials plan to move back the first bell from 9:05 to 9:15 a.m.

"This is totally unacceptable. There has got to be a better way to deal with this problem," said Darcy Diggs, president of the Westbriar Elementary PTA.

Diggs lives about four miles from the Vienna school. As it is, she said, the bus often doesn't drop off her children until 4:30 p.m.

The starting salary for Fairfax school bus drivers is $10.80 an hour. The district recently began offering $500 signing bonuses and cash incentives for employees who recruit new drivers. But the bodies just aren't out there, school officials said.

Fairfax recently tried to recruit drivers in Winchester, Va. "We talked to all of three people," Domenech said. "All we got was a lot of ill will from that school system, which is having a tough time recruiting, too."

The district also asked McDonald's Corp., one of its business partners, if it would run ads for school bus drivers on its tray covers. The fast-food chain declined to help, saying it is having a hard enough time filling its own openings, school officials said.

Staff writer Jay Mathews contributed to this report.