Dogs sniffed a brown culvert in southwest Atlanta for another missing black child today, and a police helicopter beat low over pines nearby as Lubie (Chuck) Geter, 14, was officially added to the cases of missing or murdered children that have baffled a 35-member special police task force here.

In the last 17 months, 11 children have been found murdered, and now, with Geter, five more are missing. The killings and disappearances have terrorized a city whose slogan advertises a metropolis "too busy to hate."

All the missing or murdered black children, except two, have been boys. All the boys came from low-income homes whose families say they were street-wise and not easily won over by strangers.

For that reason, police theorize the killer or killers responsible for many of the child murders -- police recently discounted a single killer theory -- had to be someone familiar to the children, or someone who could easily win their confidence, "an authority figure of some kind," speculated one officer.

Lubie Geter is the fifth child and only born to a Veterans Administration hospital chef, Lubie Sr., and his wife, Assie Lee, who works for a local dry cleaner.

While the special task force investigating the other children's cases adopted Lubie Geter's file this afternoon, Public Safety Commissioner Lee P. Brown cautioned reporters not to "assume there is a relationship to the other cases. There is no evidence that there is a relationship" yet.

Brown said police received 1,700 missing person reports last year and that in 80 percent of those cases, the individuals were found within 24 hours. The missing persons section initially handled the boy's case after his mother called the police to report him missing on Sunday. It was turned over to the special task force to investigate three days later.

Brown defended the lag time, saying police followed normal procedures. He said the missing persons section always spends 24 hours to determine whether the child is actually missing, rather than a runaway.

Until the rash of children's murders and disappearances began in July 1979, Atlanta experienced between two and seven child murders a year, say police. Those cases are usually all solved, and most are found to be domestically related, often resulting from child abuse, say police.

Lubie Geter's mother last saw him Saturday morning. He had spent some of his Christmas money buying car deodorizers wholesale to resell for profit. He was anxious to hawk his wares to shoppers at Stewart-Lakewood Mall, about five miles away. The shopping center borders an area in southwest Atlanta near where several other black children have been killed or have disappeared.

He ate breakfast and his older half-brother, Frank, drove him and a friend to the mall. His mother was cooking his favorite dinner, and she promised to save him some. He was wearing a burgundy ski jacket, a green shirt, faded jeans and his favorite penny loafers.

"Come back before dark," said Mrs. Geter, who often warned her son to be wary of strangers in the wake of reports of missing and murdered children. "People are so bad these days, someone might get you like the other children."

"Don't worry, Mom, they've got to catch me first," laughed Lubie.

He didn't come home by dark, but she figured he'd gone to a movie with his profits. Then, as the hours passed, she began pacing the floor, staying up all night.

As police searched fruitlessly around the Stewart-Lakewood shopping center, one officer familiar with the task force operations said, "It doesn't look good. The area he's missing from . . . is of great concern."