"What do you do," asks Arthur Langford, a black city councilman, "when you see two little girls, 5 and 6 years old, playing with a doll baby, and one of them says to the other, 'Don't let your baby go out, because they're killing the children.' What do you do? How do you deal with that?

"Parents are teaching their children not to trust anyone, not preacher, policeman, teacher, fireman, anyone. But when this is over, how will we teach them to trust ever again?"

Twenty black children have been murdered; two others officially are classified as missing. Twenty dead, two missing. The statistics have injected a kind of poison into the daily life of the city that holds itself up as a model of progress and cooperative race relations, that calls itself "a city too busy to hate."

There is a growing fear, expressed in ways subtle and overt, that something in Atlanta is beginning to crack.

The child killer -- or killers, as police now theorize -- holds Atlanta hostage much as the Iranian militants held America hostage for more than a year. A sense of frustration and rage has heightened racial tensions; two black communities have announced formation of armed patrols to guard their children. And, as in the Iranian situation, there is also a sense of bewilderment.

"I don't know what this thing is about," says a man walking along one of the narrow back streets around the Atlanta University complex of black colleges. "This is some kind of freak thing that the South is not used to. I'm a Georgia boy, I have been all my 34 years. This may be common in Central Park, but not in Atlanta."

The Bowen Homes housing project, a collection of low-slung, mustard-colored cinderblock buildings, is on the far western outskirts of the city. The units are arranged along curving drives and cul-de-sacs reminiscent of a middle-class suburban development, but the illusion is ruined by the litter, the bare patches of ground and the rusted-out cars in the driveways.

Curtis Walker, 13, lived in Bowen Homes. He was last seen alive Feb. 19 at a nearby shopping center. He was found March 6, dead of asphyxiation, floating in the South River across town. Number 20.

Eddie Lee George, a 33-year-old, unemployed brick mason, sits on his stoop at Bowen Homes picking over collard greens for the evening supper. He speaks softly, tentatively, searching for a way to express his frustration.

"Children around here used to be able to roam the streets," George says. "Now they can't. They can't even walk up to the store. The Walker boy used to go to school with my son. They just buried the Walker boy, you know.

"Nobody understands what's going on. It just hurts.I guess Maynard Jackson is a good mayor; he tries to do what he can do. But they don't care. The mayor, the police chief and all, they don't really care."

George looks out over the sprawling housing project with sad eyes. "I tell you one thing. When they find out who it is that's doing this, we're going to start something. Whether he's white, black or whatever, we're going to start something."

The special task force in charge of the investigation wanted to know how the killers managed to lure the children. So they sent out a team of undercover officers recently to try to get youngsters to enter a car and drive away with them.

The task force found that when the plainclothes policeman offered the child a chance to make $10 the child almost invariably climbed in without hesitation.

"They say we're vigilantes, but we're not," said Israel Green, a lanky retired postal worker, as he sat on the couch in his linoleum-floored apartment at Techwood Homes, a downtown public housing project. "We're only here to protect our community. We haven't had any incidents, and we don't want anything to happen."

Green, president of the Techwood Homes Tenants' Association, made the newspaper front pages and the evening newscasts last week when his group announced formation of an armed patrol to guard neighborhood children against the "crazed racist killer."

Many residents of the housing project say they disapprove of the plan for patrols consisting of juveniles carrying baseball bats and adults toting firearms. Many also question the involvement of Green's "consultant" -- a political activist named Chimurenga Jenga who lives across town.

Still, the patrol does have support of some Techwood residents, and later last week tenants in another housing project announced plans to arm themselves. The specter of Atlanta's public housing projects turning into armed camps gives nightmares to officials like Public Safety Commissioner Lee P. Brown, who insists. "There will be only one police force in Atlanta."

As Green and Jenga worked last week on plans for starting their patrol, with Jenga periodically dashing back into Green's kitchen to take phone calls from reporters, two police officers -- Jenga called them a "community cool-out team" -- dropped by.

"The fear is definitely there," says Office Clarence Hiley, who grew up in Atlanta. "Even beyond the children, the fear is there, in general, of the way the city is growing so fast. We're seeing things here we've never seen before. Atlanta has gotten away from the old ways, caring for people."

A day later, Hiley was one of the squad of officers that arrested Jenga for carrying a rifle in the maiden Techwood patrol.

"I'm against them," says Margie Smith, a Techwood resident, as the patrol got under way Friday. "Some of the ones with the baseball bats are the same ones you see every night around here trying to rape and mug people."

But another woman who passed the commotion of press and police marking the patrol's first outing said, "I don't blame them. I know it's white people that's doing all this. I know it."

"That's 'city too busy to hate' stuff is all nonsense," a black politican said the day the patrol started, over lunch at Paschal's, the black-owned motel that has become an Atlanta institution. "Blacks and whites may work together and even socialize together, but the bottom line is still the economic line, and blacks haven't crossed it."

Commissioner Brown is holding a community briefing on the murders at a high school in the middle of the affluent, mostly white, north side of the city, where the houses are large and new and the killings more distant.

The session draws about 30 people who listen patiently as Brown reels off facts and figures to demonstrate that the special task force investigation of the killings is the most intensive in state history. Mr. and Mrs. Charlie Devon are among those in the audience.

"I don't think Atlanta is any different at all," says Mrs. Devon. "We're all concerned. It doesn't matter which child it is, the city is concerned."

"Well," drawls Devon, "I think it might depend on which side of town you're on. Things might be different if you're not on the north side."

"I just don't think so," Mrs. Devon insists.

"Then tell me," her husband asks, "when was the last time you were in south Atlanta? When?"

"I don't know," the woman says. "I guess I don't get down there too much. But I know that Atlanta cares."

Brown handles all questions with aplomb, but he becomes agitated when a reporter asks about the psychological health of the city's poor black children who now live in fear of being snatched off the streets.

"Of course, we're concerned," he snaps. "That's one of our major problems. We're very worried about that, and we're doing all we can."

Brown tells the audience some black children have suffered bedwetting, nightmares and difficulties in school since the murders began.

And then there are the voices of the children:

"My mama's a block parent, and she be outside watching for me," says Spanada Richardson, 6. "If somebody tries to get me I'll just go into the house. I can run fast."

"I have to stay in the house most of the time now," says David Butler, 7. "It's just not as much fun."

"You be scared to go places by yourself," says Paul Anthony, 11. "You can't do the things you used to do. You can't play with your friends or go to the park without people trying to get you. It ain't no fun staying around the house. One night I had a dream that the man was coming to get me, and I was scared when I woke up.

"I wish things was the way they used to be."