Two investigations involve possible air bag malfunctions, while the others were prompted by reports the rear wheel bearings could fail and the engine could catch fire.
It is unusual for the National Highway Traffic Safety Administration to conduct four simultaneous investigations into one vehicle.
The Focus, a subcompact introduced with the 2000 model year, has been recalled eight times for problems ranging from faulty seat latches and windshield wipers to a throttle that can get stuck open.
Ford has been successful in targeting the Focus to buyers under 35. It is available in seven models, including hatchback, sedan and wagon versions, and is marketed as an affordable performance car with a striking design.
Ford has built two special editions for enthusiasts — one with a 220-watt Sony stereo system, the other with a Kona mountain bike and nylon seat covers than can be zipped off for washing.
It's the fifth best-selling car in the United States, trailing only the Honda Accord, Toyota Camry, Ford Taurus and Honda Civic.
Ford spokesman Todd Nissen said the company constantly monitors vehicle performance and moves quickly to address problems. He said it is cooperating with NHTSA.
"There is no doubt that the Focus did early on have some quality issues which we take seriously and are addressing," Nissen said.
NHTSA received reports from 16 people who said they were burned by gases when the Focus air bag deployed. Most of the cases involved second- and third-degree burns on the arms and hands of the driver. Two people said a fire ignited in the steering column.
NHTSA also is investigating 29 complaints alleging the Focus air bag deployed in a slow-speed crash or when no crash occurred. The air bag investigations cover 575,000 vehicles from the 2000-2001 model years.
The other two investigations are limited to the 2000 model year. One involves four complaints of fires in the engine compartment, near the battery. The other involves 21 complaints that the rear wheel bearings can fail, which could cause the back wheels to come off. One accident has been reported.
"Usually, when a new car comes out, there are some little glitches, but these aren't little," said Joan Claybrook, president of consumer advocacy group Public Citizen. "If I were Ford, I would get these things fixed before it becomes a Pinto."
But Ron Pinelli, an analyst with Autodata Corp. who does research for the auto industry, said recalls normally do not hurt sales.
"In most cases, the consumers kind of shrug things off," he said. "The only time when consumers really pay attention is when it's major and the recall receives a lot of media attention."
NHTSA opens any investigation with a preliminary inquiry, in which the agency and the manufacturer exchange paperwork about an alleged problem. The investigation then may be upgraded to an engineering analysis, where government engineers examine the parts to see if they are defective. An investigation can lead to a recall.
NHTSA has also upgraded a probe of the steering systems for 1.2 million Ford F150 and F250 pickup trucks. The investigation, now classified as an engineering analysis, involves 1997 and 1998 models of the F150 and F250. Thirty-four people have said they suddenly lost steering control, leading to two crashes and an injury.
NHTSA has also opened an investigation covering 1 million pickups and sport utility vehicles made by General Motors Corp. The agency has received 82 complaints alleging the throttle can stick. Three of the incidents led to crashes and four people were hurt. The investigation involves 1999 to 2001 models of the Chevrolet Silverado and Tahoe, GMC Sierra and Yukon and Cadillac Escalade.