A massive fire, started when law enforcement officials dropped an explosive device from a helicopter after an all-day siege, tonight raged through almost two blocks after destroying a fortified west Philadelphia row house serving as headquarters of MOVE, a radical back-to-nature group.

Authorities said a woman identified as Ramona Africa, the group's spokesman, and 9-year-old Bertie Africa were treated for burns but that they could not account for other adults and children thought to be in the house. Their exact numbers were unknown, and the structure was too hot to enter immediately.

Mayor W. Wilson Goode told reporters that at least three adults shot at police and firefighters behind the burning building and were thought to have escaped. At least 50 other houses burned before the blaze was brought under control just before midnight, authorities said.

"What we have out there is war," Goode said.

Police Commissioner Gregore Sambor described the device as an "explosive entry charge." And Fire Commissioner William Richmond said authorities hoped to ignite a rooftop bunker, with peep holes and weapons slots, and then extinguish the fire as it burned down to the top floor of the two-story house.

"When the fire started to move [to adjoining houses], there were shots fired. The firefighters [took] defensive positions . . . allowing the fire to move . . . . It was a hot fire, and we had the [brisk] wind," Richmond said.

Sambor said those who escaped may have used tunnels that police suspect were dug into adjoining houses after their residents were evacuated. He said a police officer was struck by a bullet fired by a fleeing adult but suffered only a bruise because he was wearing a bulletproof vest.

As the fire raged late tonight, some area residents and bystanders became irate. And tempers flared as fire and clouds of black smoke spread. Police were taunted with chants of "Murder! Murder!" Some homeowners tried to carry valuables from their residences as flames approached, and others sprinkled their rooftops with garden hoses.

The fire ended a day that began with an 80-minute gun battle, some of it involving automatic weapons, with occupants of the house, which was also blasted with water cannon. MOVE members had boasted that they were prepared to die rather than be evicted from the middle-class black neighborhood.

Between the sunrise gun battle and the fire, which began about 5:30 p.m., few sounds were heard from the house about four miles from downtown Philadelphia.

In 1978, MOVE members were involved in a shootout with police at the group's original headquarters, about three miles from today's scene. One police officer was killed and several were wounded in that encounter. MOVE has told authorities that it wants freedom for nine members convicted after the shootout.

Shortly before 6 a.m. today, Sambor ordered MOVE members to leave the house, but they refused. One person yelled from inside, "We ain't got a . . . thing to lose. So come on down and get us."

A few minutes later, a deafening barrage of gunfire began, continuing until 7:20 a.m. "The gunfire was steady and louder than anything I've ever heard," said Chris Watson, 22, who said he lives two blocks away.

Police Lt. Al Lewis said police fired "solely from a reactive posture." Authorities said that between 7,000 and 10,000 rounds of ammunition were fired into the house.

Lewis said police had arrest warrants charging four MOVE members believed to be inside the house with making terrorist threats, harassment, possession of explosives and conspiracy.

Police had moved in just before dawn, firing tear gas and directing a powerful water cannon at the structure. Later, they doused the house for five hours with the cannon, which propels 2,000 gallons a minute, turning the front of the house into rubble but leaving the rooftop bunkers less damaged.

After hours of inaction and siege by hundreds of heavily armed police, a huge explosion was heard and the fire started as the helicopter passed over about 5:30 p.m.

This afternoon, clergymen and relatives of MOVE members had attempted to contact those in the house. "We told them they couldn't win," said Stanley Vaughn, a member of the negotiating team. "We pointed out that there were children involved, and they could be sent out." There was no response.

In mid-afternoon, Goode told reporters that the city was determined to evict the group and said, "We intend to seize control of the house by any means necessary. I am totally convinced that the organization is bent on a violent confrontation."

"This is a travesty," said Harry Waters, who had urged city officials to evict MOVE from the rat-infested, debris-strewn house on grounds that it was a neighborhood blight and that MOVE members harassed neighbors.

"This isn't what we expected. We expected people negotiations, not bombs, guns and bullets," Waters said.

Janice Walker, who lived two doors from MOVE headquarters, said she was heartbroken as fire destroyed her home. "We've lived here 20 years," she said. "My family and all its dreams and aspirations were tied up in that house. I want to know who's going to pay for it. It's just not fair for some back-to-nature group to destroy our neighborhood."

MOVE is a small, radical group of about 100 members, founded in 1972 by Vincent Leaphart, a black handyman with a third-grade education, and Donald Glassey, a white college instructor and antiwar activist. The initials MOVE do not stand for anything.

Leaphart, who changed his name to John Africa, contended that modern technology was destroying society and led several demonstrations, including some against the Board of Education, Jesse L. Jackson and the Communist Party.

MOVE members adopted Africa as their surname and said they ate only natural foods, often uncooked, and avoided contact with any bureaucracy. Neighbors complained that MOVE members violated housing health codes, fed dog meat to their children and left babies unclothed.

Late Sunday, police began evacuating the neighborhood around the house, which had been fortified with sandbags and other protective devices.

Two weeks ago, residents had asked Goode to have MOVE evicted.

Louise James, owner of the house and mother of one MOVE member, criticized police and Goode for the eviction decision.

"I want the mayor of Philadelphia to stand in front of my face and justify his position," she said. "I told him over and over and over that MOVE would not come out of that house, and Wilson Goode knows it."