A Landover Hills mother and her two children died in a four-alarm fire in their home early yesterday morning.

Debra Lynn Caldwell, 26, was found dead in the living room of her modest split-level frame house after neighbors reported smoke coming out of the first floor windows at 2:20 a.m., fire officials said. Six-year-old Perry Caldwell Jr. and 4-year-old Jason Robert Caldwell were found overcome by smoke in their bedrooms, according to fire spokesman Jim Mundy.

Perry Jr. died enroute to nearby Prince George's General Hospital but his brother was dead at the scene, Mundy said.

The cause of the fire, which officials say may have burned for some time before it was reported, is under investigation. Fire officials said it began and was centered in the living room but heavy concentrations of smoke filled the entire house. Damage was estimated at $60,000 to the house and $20,000 to its contents.

Neighbor David Miller gave a hand to the first fire truck on the scene.

"I hollered to my wife 'Debby's house is on fire' and ran out the front door," said Miller. "They handed the oldest one out the window to me. A fireman started working on him, but at that point he was gone."

Mrs. Caldwell, who recently was divorced from D.C. police officer Perry T. Caldwell, lived in the house with her two children.

One friend of the family said Mrs. Caldwell usually slept on the overstuffed living room couch, with the second floor master bedroom closed off to save heat. Often, the neighbor said, the boys joined their mother with blankets on the floor, though they had their own separate bedrooms.

"She was quite devoted to her children," said Doris Simms, office manager of the film distribution company where Caldwell worked as a $230-per-week secretary. "She brought them in all the time. She was really excited over what she was getting them for Christmas," Simms added.

"She had a good sense of humor but the thing was that she had a great big heart. She would do anything for anyone," Simms said.

Fire department spokesman Mundy said that the deaths might have been avoided if the house had been equipped with a working smoke detector.

"Of all the factors the biggest and most important is no smoke detector," the 20-year fireman said. "We have never had a case where anyone has died in a fire where there was a working smoke detector. It's hard for me to comprehend why people don't spend that small sum of money."