NICE, France (AP) _ Hundreds of firefighters battled a blaze in a forest north of Nice today that has left three men dead and scorched more than 500 acres of trees, the French news agency reported.

About 300 firemen fought to contain the fire that began Sunday in the forest that was a tinderbox as a result of the unusually dry weather, Agence- France Presse reported.

It was not known exactly what sparked the fire near the village of Saint- Martin Vesubie, 40 miles northeast of Nice.

France has been experiencing the driest winter in more than a quarter century and no rain has fallen in the area north of the French Riviera since Dec. 1. By mid-January an average of eight-tenths of an inch of rain had fallen nationwide instead of the usual 2.4 inches.

''The fire smolders under the trees and springs up in the least gust of wind,'' an unidentified fireman told AFP.

On Thursday afternoon, a National Forest Office worker died after rocks and branches fell on him while he was fighting the fire, AFP said. Ben Abdallah Djouari, a 50-year-old father of eight children, died from injuries to his head after being pushed by the debris into a 165-foot-deep ravine.

Two men with Djouari were struck by falling rocks and were evacuated by helicopter, the news agency reported.

Also on Thursday, an ambulance carrying an injured firefighter, Sebastien Antraygues, slid off the road and into a ravine, killing him. Angraygues, 21, had been working in the forest since Sunday.

The driver of the ambulance was seriously injured in the accident. A number of other firefighters suffered minor injuries.

On Tuesday, fireman Paul Brutus, 50, was found dead from unknown causes in an area where he had been working.