The 10-year-old boy who ran for help and later described in detail how two teen-agers attacked his friend, Steven Wilson Jr., 7, in Turkey Branch Creek last Friday was charged yesterday with the assault, Montgomery County police reported.

Police charged the 10-year-old with assault with intent to maim and filing a false report of a crime. His name is not being used in this story because he is a juvenile.

"Consideration of his involvement was always open," Police Chief Bernard D. Crooke said.

The 10-year-old had originally told police that he and Steven had been playing at a creek in their Aspen Hill neighborhood when they were attacked by older teen-agers wielding fold-up knives. The 10-year-old said he had escaped up a steep embankment but that Steven had fallen and been attacked by the teen-agers. Police issued composite pictures of the attackers based on the 10-year-old's descriptions and combed the neighborhood looking for clues.

But it wasn't until yesterday that the 10-year-old's story began to crumble, Crooke said. Investigators felt that the boy's description was "too much and too good for a 10-year-old running for his life," police said. The break in the investigation apparently came during police questioning at the Wheaton station where the boy was taken after he attempted to run away from home Monday night.

After being notified by the boy's mother that he was gone, police launched a widespread search, with officers going door to door in some neighborhoods. Police said that a patrol officer found the boy unharmed at about 10 a.m. yesterday in the Twinbrooks area, not far from his home.

About three hours later police issued a statement that the case was closed and that they were centering their investigation on the 10-year-old. The charges were filed against him later in the afternoon.

He was being held at the Noyes Juvenile Detention Center in Rockville last night, police said. The boy, wearing shorts and a red jersey, was taken from the police station by detectives about 6 p.m. He is scheduled to appear in juvenile court today.

Shocked disbelief was the initial reaction in Aspen Hill to the news that the 10-year-old had been charged. The boy's family, which is from Ethiopia, had lived in the neighborhood less than a year, neighbors and police said. His father was believed to live in New York, according to police.

"I don't see how [the 10-year-old] could have done that much damage to Stevie," said John Milcetich, 39. "It is totally bizarre . . . they were good friends."

Other residents expressed bewilderment at how the 10-year-old could have inflicted the injuries without getting any blood on his clothes.

Police sources, however, suggested that the 10-year-old could have thrown rocks at Steven from far enough away to have avoided the blood. They also said that there may have been enough water in the creek for the 10-year-old to have cleaned off any blood.

Rebecca Jaquay, who lives near the 10-year-old's family, said her son had played with the 10-year-old and his brother often and her only concern was that "they played rough a lot."

Steven, who suffered multiple lacerations and head injuries in the Friday attack, continued to improve. A spokesman for Children's Hospital said that boy's condition has been upgraded from critical to good, and friends say that he may be able to go home later this week. Friends who visited him said he has no memory of how he was hurt or who hurt him.

After the assault, the 10-year-old notified Steven's father, who rushed to the creek and found his son unconscious face-down in the water. Police investigators then put together composites of the two teen-agers, based on the quick description provided by the 10-year-old.

"We used a potato head identification kit," said police spokesman Harry Geehreng. With the kit, features can be added or removed based on witnesses' recollections.

As citizen concern about the incident grew over the weekend, and details of the viciousness of the attack were released, the manhunt intensified. Chief Crooke said that investigators were flooded with about 500 telephone calls from citizens offering information that they hoped would lead to the arrest of the attackers.

Crooke said police had been working around the clock to check out all possible leads. "We put everything we had available into this," he said.

The 10-year-old, meanwhile, stuck to his story, telling it over and over again, precisely and with confidence, according to police. On Monday night he told it to a television news crew, although he was not identified and his face was not shown on the news broadcasts.

But about the time that the interview was shown on the late night news, the boy's mother was telephoning police to say that her son was missing, officials said.

Nick Scholz, 36, a neighbor who helped administer first aid while awaiting an ambulance rescue team last Friday, was at Children's Hospital with the Wilsons when a county social worker called to say that police suspected the 10-year-old.

"Debbie [Steven's mother] asked me to step out of Stevie's room with her for a minute. I did and she said, 'They say it's [the 10-year-old]. Do you think that he could have inflicted that kind of damage on Stevie?' "

Scholz said he told Steven's mother: "I don't know -- the kind of sharp rocks they have down there in the creek -- I guess he could."

Late yesterday, after hearing that the 10-year-old had been charged officially, Scholz broke into tears. "This makes you want to put your fist through the wall."