An elderly woman who taught sewing in her Prince George's County home and her daughter, a secretary for a Washington legal firm, were killed early yesterday morning when fire engulfed their two-story residence.

Fire officials said yesterday that the fire at 4803 Sheridan St. in Riverdale Park was started by a cigarette left carelessly burning in a first-floor sitting room. Neighbors said yesterday that the two women had recently added the room at a cost of $9,000 to their modest brick house.

When fire trucks arrived in the residential neighborhood yesterday morning at 1:54, smoke and flames were already billowing from the second floor bedroom where the two women, Gladys Kennedy and her daughter Betty Jean Carroll, slept.

The bodies of the two women were sent yesterday to the state medical examiner's office in Baltimore to determine the cause of death.

As neighbors peered into the wreckage of the house - all but a table and a few clay figurines were charred black - Margaret Uber, a neighbor, said she was awakened yesterday morning by the glare of flames and the loud explosion of windows popping from their frames.

Uber's husband, Edwin, said he immediately called the fire department and then ran next door and began pounding on the door to awaken the sleeping women.

"I pounded and pounded on the door and it kept getting hotter and hotter," Uber said.

Kennedy was in her 70s and was active in area senior citizens groups, Edwin Uber said. Recently, he said, she had had some difficulty in walking because of several hip operations.

"Every day she would take a walk and try to get a little further down the street," said Dorothy Watson, another neighbor, as she looked over the burnt bushes and shell of the house.

Margaret Uber said that Kennedy had lived for several years in the Panama Canal Zone and still remained active in a canal zone club in Virginia. She said she thought Carroll and Kennedy's other daughter, Helen Barnes, who lives in Tennessee, had been born in the Canal Zone.

Uber said she had last seen Kennedy yesterday afternoon when she came to the doorstep of the house to watch her two white poodles run around in the backyard. The dogs died in the fire.

Uber said she last saw the daughter when Carroll parked her red station wagon in the carport. The car and carport were not touched by the fire.

"They were so proud of their home," Uber siad. "They had just put a lot of work into it - the addition, an air-conditioning system. It's just so sad."

Watson and other neighbors also said that the mother and daughter were "interested in everything and on the go all the time. They were just real nice people."