WASHINGTON — They fix planes and load and unload heavy bags in sweltering heat and frigid cold. For many passengers, they are invisible, though they toil right underfoot.

Airport ground workers do their jobs amid roaring aircraft engines and the arrival and departure of tanker-size jetliners. They must avoid stepping in oil slicks and watch out for baggage carts whizzing by.

Now the ground workers' tough conditions are coming under closer scrutiny. For the first time, airlines and the Federal Aviation Administration will co-host a three-day symposium focused on improving safety on the tarmac at the nation's airports. Participants in the gathering, which begins Sept. 6, will analyze data on accidents to help airlines identify dangers and adopt strategies for reducing risks.

"It's next in line to be dealt with," said Basil J. Barimo, vice president of operations and safety for the Air Transport Association, a trade group that represents major U.S. airlines.

While serious injuries and death occur, the most common injuries among ground workers result from heavy lifting, in many cases causing severe back strain. According to figures from the Bureau of Labor Statistics, there were 4.53 injuries and deaths per 100 airport ground workers in 2004, the latest year for which data are available. By comparison, coal miners had a rate of 6.58 injuries and fatalities per 100 workers; in construction, the rate was 5.77.

So far this year, four ground workers have been killed or seriously injured, according to data collected by The Washington Post. In one accident, a mechanic died in January when he was sucked into the engine of a Continental Airlines aircraft at El Paso International Airport. A month later, a baggage handler for Comair, a Delta regional carrier, was killed when struck by a baggage cart at the Detroit airport. Three serious or deadly accidents occurred in 2005 and two in 2004.

Through the busy summer season, ground workers have been under increased pressure to load and unload bags swiftly and to ensure that the aircraft are prepared for safe travel. Many financially strapped carriers have reduced their staffs, increasing workloads. Some airlines have been hiring ground workers at lower wages to cut costs.

Several airlines said training and supervision of workers remained as much a priority as passenger safety.

Many workers and their families say more needs to be done to ensure a safer environment, and they urge more oversight. FAA officials said they review each airline's safety guidelines for the workers but that it was up to the airlines to enforce those rules.

Kenneth Rosenman, a physician and professor at Michigan State University who in May published a three-year investigation on workplace injuries and illnesses in Michigan, said only about 40 percent of job injuries or fatalities are reported. He said employees and companies think there's little incentive to report accidents to federal authorities.

Jim Ballough, director of the FAA's flight standards service, said the agency sends inspectors to assess flight preparations and ground safety. But some airline officials said those random inspections focus more on flight matters than on ground safety. The officials added that workers need more protection.

Workers complain that oversight shifts among agencies. After an accident, the agency that leads the investigation varies, depending on the type of accident. Further, no one entity — not the FAA, the National Transportation Safety Board, Occupational Safety and Health Administration, the Bureau of Labor Statistics, the airline association nor unions — keeps comprehensive records of injuries and deaths among ground workers.

Paul Kempinski, director of ground safety for the International Association of Machinists & Aerospace Workers District 141, said unions have urged Washington to more rigorously monitor ground operations. OSHA "only comes out when something happens," said Kempinski, who represents baggage handlers at United and Aloha airlines and US Airways. "Something needs to be done sooner. Someone needs to be in charge of oversight."