When Wally Roberts saw the mangled body of Deborah Pernell, he knew instantly that she had been killed in her bed by his pit bull terrier, Napoleon.

''Debbie`s body was all chewed up,'' Roberts recalled. ''Her entire face had been chewed away. Her scalp was gone. Napoleon was standing beside the bed. He was covered with blood. There was this look on his face that said, `I fouled up real bad.` ''

Napoleon, who paid with his own life for the fatal attack, was of a breed that critics charge are killer dogs beyond redemption. They demand legislation to control them.

Ironically, their unsavory reputation has boosted the popularity of the dogs originally bred to fight each other in pits.

In many parts of the United States they still are bred to fight and do, although dog fighting is illegal in all states and a felony offense in 26. But, like most victims of attacks by pit bulls, Pernell was killed last February in Phoenix by one kept as a pet, not to fight.

''Napoleon was my best friend,'' said Roberts, 43, who works at a graphics design studio. He is a physical fitness buff who races mountain bikes as a hobby.

Roberts bought Napoleon in 1981 from a Chicago breeder. Napoleon, who grew to 75 pounds, was registered by the American Kennel Club as an American Staffordshire Terrier, the breed name preferred by the AKC, which opposes dog fighting.

But the Staffordshire is the same breed as the American pit bull terrier, once bred exclusively to fight and still known for its courage, strength and powerful jaws.

''The fighting has got out of hand,'' Roberts said. ''A different dog is emerging. Some people are breeding these dogs just to fight. There`s too much inbreeding.''

Although Napoleon had bitten at least two people before he attacked Pernell, 33, who was living in Roberts` home, the dog`s owner insists that the killing was ''a freak accident.''

''When I came into the bedroom, I thought at first she had blown her head off with my pistol,'' Roberts said. ''There was blood all over the place. Napoleon was standing right beside her. He just looked at me like he knew he had blown it. I don`t think I`ll ever be able to lose that picture in my mind of finding Debbie that way. I have nightmares about it.''

Roberts said he feels remorse but not guilt or responsibility for Pernell`s death.

''I met with a priest,'' he said. ''He told me to feel the pain but not the guilt. I had nothing to do with what happened.''

Some of the pain Roberts feels is because authorities had to ''put down'' Napoleon.

''I miss my dog a lot,'' he said. ''He really was my best friend.''

Then, Roberts added, ''Of course, I miss my friend Debbie, too. She was a good lady.''

Robert Baker`s specialty for the Humane Society of the United States is tipping off law enforcement officers on when and where dog fights are to be held. It is dangerous undercover work that has taught him a lot about pit bull terriers and the kind of people who own them.

''Attacks on humans are increasing in direct proportion to the growing popularity of the breed,'' Baker said in an interview at the society`s headquarters in Washington.

He has no national statistics but is keeping an ever-thickening folder crammed with accounts of the attacks.

On March 28, Helen Harder, 87, was attacked by a pit bull while raking leaves in her yard in Independence, Mo. One of two pit bulls leaped a fence from a yard next door and and bit her on the face and throat in an attack that lasted just 30 seconds and left her with a broken leg.

Baker finds it ironic that news coverage of the society`s long opposition to dog fighting has made the pit bull terrier more popular.

''People started buying them for the sole purpose of having the meanest dog on the block,'' he said. ''It`s a macho thing. The ones who don`t fight their dogs own them for the same reasons as the people who do. Because of the growing popularity of the breed, we now find pit bulls running around loose and people being torn apart.''

Baker concedes that pit bulls may be no more likely to attack humans than some other breeds.

''The problem is the severity of the attacks,'' he said. ''When a pit bull attacks a human, the damage is devastating.''

Marcellus Hampton died horribly at the age of 11 after tripping while playing on his front porch in Cincinnati and falling within reach of his family`s pit bull, named Buddy, who was chained to the side of the house.

''The dog grabbed him by the head and dragged him up and down the steps,'' a witness reported. ''Then the dog had him by the throat.''

Buddy`s powerful bite severed the boy`s carotid artery, main supplier of blood to the head.

That 1983 killing and other attacks prompted the city council to approve an ordinance banning the sale of pit bull terriers and requiring that they be kept fenced in or muzzled and on a leash. A proposal that would have banned the breed from Cincinnati was defeated.

Hollywood, Fla., got pit bull control legislation after a series of attacks, including an incident in which an elderly woman was left naked and bleeding after her two dogs turned on her. That legislation was overturned in the courts, but many other communities now have tough ordinances to control the breed.

Such legislation is bitterly attacked by the breed`s supporters, such as Ralph Greenwood of Salt Lake City, president of the American Dog Breeders Association.

His organization, which Baker and others in the Humane Society charge is

''a front for dog fighting,'' registers the breed under the name American Pit Bull Terrier.

''Dog fighting is against the law,'' Greenwood said, spelling out his organization`s official position. ''We don`t sanction or encourage anything illegal. We have no way of knowing if the dogs we register are fighters.''

As for his personal view of dog fighting, Greenwood does not consider the practice cruel.

''It`s like racing horses,'' he said. ''It`s been built up into more than it is.''

Pit bulls love to fight, Greenwood insisted.

Fighting dogs have been known to die in the pit with their tails still up and wagging, which some take as evidence that they are bred to a ''blood sport'' they love.

Pit bulls do not even growl when they fight, sometimes for several hours. Losers do not always die in the pit, but sometimes winners, as well as losers, die of their wounds. Five-time winners are dubbed grand champions and command top stud fees.

Sometimes losers are shot by disgruntled owners. Wounded dogs rarely are taken to veterinarians for fear the owners will be reported.