LOS ANGELES (AP) _ Firefighters used chemical-laden air tankers Tuesday to battle Southern California wildfires that had burned at least 43,000 acres and 22 houses, and killed a man defending his home from the flames.

Arson was suspected in three of the major fires, officials said.

Federal and state workers joined local firefighters at hot spots across a 100-mile, four-county area from the coast west of Los Angeles to San Bernardino County.

Pepperdine University canceled classes Tuesday because the main artery through the area, Pacific Coast Highway, was closed to all but emergency traffic about 8 a.m. Two Malibu-area elementary schools were also closed, and bus service for Santa Monica High School students was canceled.

Hot, dry desert winds had lowered the humidity to 10 percent, turning parched brushland into a firefighters' nightmare, and on Tuesday airplanes laden with fire-snuffing chemicals targeted two blazes roaring near Malibu.

The Santa Ana winds, which blew persistently Monday, died down Tuesday, said county fire inspector Mike Pearson.

''We had the fire burning right up to the walls of the (Malibu) sheriff's office'' Tuesday morning, said Los Angeles County sheriff's Sgt. Ronald Wallach. ''It was like being within 100 yards of a napalm strike.''

Officials said one man dropped dead of a heart attack while helping firefighters defend his home Monday in Box Canyon, about 30 miles northwest of downtown Los Angeles.

In Piuma Canyon, a blaze burned an estimated 3,300 acres, destroying its sixth house and blackening the earth for two miles around the Malibu civic center, 30 miles west of downtown Los Angeles, Wallach said. The blaze was reported 30 percent contained Tuesday afternoon. ''We have a saying around here: They'll stop it at the kelp line,'' he quipped. ''We haven't lost any beach yet.''

A second fire that broke out in nearby Decker Canyon had burned across 5,800 acres, but no structures were threatened, said county fire Capt. Gordon Pearson. It had burned four houses and a garage Monday, but was reported 50 percent contained at noon.

''Arson is always suspected in fires like these,'' Pearson said, adding it was probably more than ''a strange coincidence three fires started within 45 minutes in the same general area.''

Eight air tankers began dumping chemicals just after dawn on the Piuma and Decker Canyon fires, as fire officials hoped to gain an upper hand. Pearson was cautiously optimistic Tuesday afternoon.

''We're starting to get some containment'' he said, but no projections for control had been made.

In Wheeler Canyon, 50 miles northwest of Los Angeles and a few miles north of Santa Paula, six homes, two trailers and several outbuildings were destroyed by a 14,000-acre blaze that combined with another fire and raged untamed Tuesday, said U.S. Forest Service spokeswoman Kathy Good.

In Ventura County, two fires combined a few miles north of Santa Paula and about 50 miles northwest of Los Angeles, consuming six homes, two trailers and several outbuildings and cars, said U.S. Forest Services spokeswoman Kathy Good. The fire was estimated at 14,000 acres Tuesday afternoon, Ms. Good said.

Three other Ventura County fires estimated at more than 1,000 acres each were reported out of control Tuesday afternoon, said Hank Weston, spokesman for the California Department of Forestry. No structures were lost, but the Peach Hill fire seven miles north of Thousand Oaks threatened 200-300 homes and evacuations had been ordered, he said.

The Box Canyon blaze burned about 1,600 acres by Tuesday morning and was 99 percent contained. Box Canyon Road residents said at least one home there burned.

On Mount Gleason 25 miles north of downtown Los Angeles, 1,000 acres were consumed by Tuesday afternoon in an out-of-control timber fire, said forest service spokeswoman Susan Marzec.

National Weather Service meteorologist Frankie Shaw said winds were gusting up to 28 mph in some Southern California areas, compared with 50 mph Monday. The relative humidity was 10 percent or lower and temperatures were in the 80s.

Johannes Leembruggen, 59, suffered a fatal heart attack Monday at his home, Pearson said.