By 7:15 a.m. each weekday at Broad Run High School's bus lot, several drivers unhook car seats and carry diaper bags from their minivans and Ford Expeditions to their 40-foot-long yellow buses. They are trailed by sleepy toddlers, who suck their thumbs and drag blankets and stuffed bears and dinosaurs aboard the buses' front seats.

Tanja Brandt, of Cascades, brings the car seat so her 2 1/2-year-old daughter, Shanna, can ride the bus in the mornings. Her 6-year-old son, Connor, accompanies her on the after-school runs. Brandt, who once did title work at a car dealership, estimates that she saves $900 a month in all-day and after-school child-care costs by driving a bus instead.

As a brisk economy and growing student enrollments fuel a nationwide shortage of school bus drivers, more and more stay-at-home moms are getting behind the wheel in Loudoun County. But school officials said they are desperate to hire 20 more drivers.

"That's been our saving grace--the mom who drives for us," said J. Michael Lunsford, director of transportation for Loudoun schools. "If it wasn't for those folks, we'd be out of business."

Mothers said bringing their young children to work beats paying for child care.

"I do it because I wanted to be home with my kids but still have a job," said Brandt, 35, as she checked the gauges on her 10-ton vehicle one brisk morning. "I can bring my kids and still be home with them on snow days and holidays."

After a month-long training class in which they learned CPR, safe-driving techniques and how to check the oil and refuel, some mothers joked that driving a bus wasn't too different from driving their vans and sport utility vehicles.

Despite the cacophony of kids and her own frustration at the occasional motorist who passes her red flashing lights as she drops off a child, Karen Archer, of Sterling Park, said driving a bus is much less stressful than her former job as an ordering clerk for Giant Food.

"It's really easier because I don't have to worry about what to do with my child--and if he's sick, I can call in and get a substitute," Archer said as she pumped gas into her bus at Broad Run. There is a small pool of available substitutes. But in these lean times, trained personnel in the school transportation office--secretaries, maintenance people, administrators--sometimes take a route. In other instances, regular drivers are given extra routes.

Offering such incentives as health care benefits and a way around child care, school districts across the country are recruiting mothers as drivers.

"One of the prime recruiting grounds in the past three or four years are PTA meetings," said Michael J. Martin, executive director of the National Association for Pupil Transportation in Albany, N.Y. "These are people willing to donate time to enhance their child's educations."

Fewer people want to work part time, experts said, and those who do can easily find a job with less responsibility and stress than driving a bus full of children.

In most Washington area school districts, bus drivers must complete a month of classroom instruction and on-the-road training. They must obtain a commercial driver's license, and pass a criminal background check and several random tests for drugs and alcohol.

And after all that, Loudoun bus drivers get $11.21 an hour. The typical driver works about 3 1/2 to 4 1/2 hours a day. Some are able to pick up extra hours by driving for field trips or taking a kindergarten run at midday.

If he hired 20 more drivers, Lunsford said, he would add 15 bus routes. The district's goal is no more than a one-hour commute for each child, but some students are traveling for nearly 90 minutes. Other buses are packed.

Stephanie Edwards, 31, who drives in the western end of the county, said she has seen her route go from 12 students last year to about 56 this year.

"The county's growing, and we're certainly feeling it," she said. "Everybody wants to move out to get away from all that congestion, but they're bringing all their kids with them. The other runs are already overcrowded, so they put them on mine."

In Howard County, a deficit of 20 drivers has meant that David C. Drown, supervisor of school transportation, has been attending job fairs, advertising in the newspaper and even putting help-wanted signs in the school bus windows.

"It's tight, and it's getting tighter as the year goes on," Drown said. "We'll suffer along and do what we gotta do to get through the crisis."

The shortage in Fairfax County schools is minimal, said Jim E. Vaglia, director of transportation for Northern Virginia's largest school district. To attract new drivers, school officials have promised a $500 bonus for new hires after 90 days on the job and $500 to the Fairfax school employee who recruited them. Loudoun does not have money for bonuses, local officials said.

"That did help us," Vaglia said. The robust economy "is a real bear for us right now."

Once-rural Loudoun used to recruit farmers to drive school buses, Lunsford said. They got health benefits and could do their farm work between morning and afternoon runs. But as the number of farmers dwindles, those drivers are being replaced with mostly stay-at-home moms.

"This is a good mom job for me," said Cindy Trotta, 34, who has been driving routes in Ashburn for about 18 months. "It gets me up, gets me going and I can drive my daughter to school and get paid for it."

Aboard Trotta's bus, No. 222, she keeps tabs on her morning riders through her rearview mirror and an occasional call on her intercom. A former real estate agent, Trotta has instituted her own policy: "Discipline them just like they're your own children."

"My rules are just for them to stay seated for their own safety," Trotta said as a group of middle schoolers squeezed onto the bus. A few minutes down the road, Trotta glanced in her mirror to see a few young boys leaning over seat backs to pass CDs to each other and standing up to switch seats.

"Hey, I need everybody to sit down back there," she called over the intercom. Within seconds, most of the boys faced forward in their seats and settled down. A few called back: "Okay, Miss Bus Driver." She smiled at them in the mirror.

"She doesn't pull any punches," said Patrick Meserole, 13, who rides Trotta's bus to Farmwell Station Middle School, where he is a seventh-grader. "Sometimes it can sound like a volcano in here. She won't hesitate to tell them, 'BE QUIET!' " he yelled before adding: "But she does it in a nicer manner."

CAPTION: Cindy Trotta drops children off at Cedar Lane Elementary. "My rules are just for them to stay seated for their own safety," she said.

CAPTION: Before going out on her run, Cindy Trotta checks the oil. She has been driving routes for about 18 months.

CAPTION: Tanja Brandt's daughter Shanna looks out from her mother's seat after finishing their morning run. Her brother Connor comes along in the afternoon.