As the grieving continued for the two young children who died locked in a car Thursday, authorities took custody of their siblings yesterday and acted on several fronts to find out how the children came to be in the car and whether D.C. police response was adequate.

Autopsy results showed that Iesha Elmore, 4, and her 2-year-old brother, Clendon, died from "exposure to extensive heat, critical hyperthermia" and "asphyxia by suffocation," said Linda Wharton-Boyd, public information officer for the D.C. Department of Human Resources. "While in the car, they ran out of oxygen."

She said chemical tests to verify the cause of death would not be completed for several weeks.

There was no sign of foul play, according to a police source familiar with the case, who said "there is nothing so far to contradict" what Rose Elmore, the children's mother, has told police about realizing her children were missing, searching for them and finding them in a locked car on a cruelly hot afternoon.

However, as the police department's homicide and youth services divisions continued their investigation of the children's deaths and whether neglect played any part, three siblings of the two dead children were removed from their mother's custody in a hearing yesterday in D.C. Superior Court. The children -- ages 6, 5 and 7 months -- were placed with their paternal grandparents pending the outcome of the investigation.

Meanwhile, Acting D.C. Police Chief Larry D. Soulsby ordered an investigation into residents' complaints that police did not act properly when called to the Southeast Washington neighborhood where the two children were found. The children were pulled unresponsive from a red Pontiac Fiero sports car parked in the 200 block of 37th Place SE by a bystander who had smashed a window. The children were pronounced dead at D.C. General Hospital 90 minutes later after doctors tried to revive them. A police source said it is highly probable that the children were dead when removed from the car.

Soulsby said he had directed Inspector John Daniels, commander of the 6th District, to examine allegations that the first police officer to arrive on the scene failed to break into the sweltering car and extricate the children. Residents of the area also said the officer, identified by sources as Daniel Lee, as well as other officers, did not try to revive the children with cardiopulmonary resuscitation.

"I'm greatly concerned about these complaints, and we're going to get to the bottom of them," Soulsby said. "Why he didn't break the window if he didn't and why he didn't give them CPR if he didn't -- we don't know. Those are the kinds of questions we want answered."

Soulsby visited the neighborhood yesterday where the children lived and saw where they died. The lot where the car was parked is less than 30 yards from the apartment where the children lived with their mother, siblings and grandparents. The car had been bought last Saturday by a woman who lives in the neighborhood and recently was being repaired by the grandfather of the dead children.

"What is missing is part of our hearts," Barbara Elmore, the children's grandmother, said yesterday. "It was like somebody reached in and took something that will never be whole again."

Elmore said her daughter is "devastated. No one can imagine her grief."

Children from the neighborhood crafted a memorial of stones and flowers, marking the spot where the children died. Some had written signs: "Love thy neighbors and thy children. R.I.P. Love, Cookie." "Gone but not forgotten." "Our Children. Our Shame."

Some of the children sought out Soulsby, taking him by the hand and asking his help in getting a safe place to play.

Kevin Davis, 12, said children in the neighborhood often play in abandoned cars because they are afraid to go to the Benning Stoddart Recreation Center and a nearby playground for fear of bullies and drug dealers.

Beatrice Blondheim, a next-door neighbor, said Rose Elmore told her that she was filling a purple plastic swimming pool in her back yard about 10 a.m. Thursday when Iesha and Clendon disappeared. Blondheim said Elmore began an immediate search for her children, going door to door with a picture, asking whether anyone had seen them. Police said they received a 911 call at 4:37 p.m. and dispatched a car, which arrived at 4:45 p.m. The children were found at 4:50 p.m. Bronson Carter, 31, said he was visiting his aunt when Rose Elmore asked him about 4:45 if he had seen the children. He said she was joined by a police officer a few minutes later when a woman approached and said something. "I heard her say: No! No! No!' And she ran to the red car with the police officer," Carter said.

Carter said he arrived at the car to find Elmore sobbing hysterically as she looked inside. The children "looked blue," Carter said, and both had their eyes open and "weren't moving." Carter said the officer was standing near the car, holding a rusted piece of bed railing.

Carter said he asked the officer: "Why can't you open the door? Why can't you bust the windows?" The officer, according to Carter, stood motionless, staring into the car, and said, "I'm doing the best I can."

Carter said he grabbed the rail from the officer and smashed out the back window and the passenger window. He said he ran to the right door and tried to open it, "but the lock was jammed and it wouldn't {immediately} open." Police said tests will be conducted on the car Monday.

Carter said he and the officer placed the children on the ground. Carter said he began doing CPR on the girl. He said the officers asked for ice and cold water but did not try to resuscitate the children.

People who gathered said that an officer asked "if anybody knew CPR" but that when a woman sent for her niece, a nurse, they refused to let the nurse work on the children.

The alleged failure of officers to do CPR is one part of the department's probe. Lee, who joined the department in 1991 and has been assigned to the 6th District the entire time, was trained in CPR at the police academy, as are other officers.

Some police officers said that they are not required to get recertified on an annual basis, as is required by accredited police departments, and that the D.C. police department does not give them time on the job to complete the eight-hour recertification process.

Sources said Lee appeared disturbed after he returned to the station. "He was very, very upset," said an officer who asked not to be identified. "You could tell it really affected him. Everybody out there seemed to be upset because it was two kids who died. One guy was saying that they were really beautiful and how it was really sad that they had their little eyes open." Lee will continue on street duty. CAPTION: Tarea Thomas, left, and an unidentified girl arrange stones, flowers and signs left in memory of Iesha Elmore, 4, and her 2-year-old brother, Clendon. Among the messages: "Gone but not forgotten" and "Our Children. Our Shame." CAPTION: Clendon Elmore, 2, left, and his sister Iesha, 4, died of a lack of oxygen in the car, a D.C. police source said. CAPTION: Bronson Carter said he smashed out two of the car windows when he saw the children inside. They "looked blue" and "weren't moving," he said.