A 40-year-old Washington woman was killed late Monday when her clothing became entangled in an escalator at the Rhode Island Avenue Metro station and she was strangled. It was the second time in the 13-year history of the area's rail transit system that a person was strangled in accidents on Metro's escalators, which are used by most of the system's estimated 500,000 weekday riders to enter and exit stations. A third Metro passenger was electrocuted by a defective light fixture alongside an escalator. On Friday, a woman was seriously injured after an escalator at the Brookland-Catholic University station jolted her to the ground, then snagged her clothing. She was freed by a bystander. The death Monday of Peggy A. Billups of Northeast Washington was clouded in uncertainty because she was legally drunk at the time of the accident, according to doctors who conducted the autopsy yesterday. The blood alcohol level in Billups' body had not been calibrated late yesterday, but Dr. Beverly Coleman-Miller said, "There was no question that she was legally drunk." For this reason, the doctors said, it was not clear whether her fall was caused by the escalator or whether she could have avoided the accident or maneuvered out of the clothing that strangled her. No one witnessed the accident. The attendant at the Red Line station said he heard a loud noise about 10:57 p.m. Monday and went to the foot of the north escalator, where he discovered Billups lying unconscious. The attendant apparently did not describe in his report of the accident how he found Billups, and Metro would not provide additional details. A spokesman for the city's paramedics said that rescue workers had to cut off parts of Billups' clothing in order to free her. She was pronounced dead at Washington Hospital Center at 11:47 p.m. Billups, who lived in the 1200 block of Franklin Street NE, worked at the Potomac Electric Power Co. cafeteria downtown. She got off work about 10 p.m. and usually arrives at the station between 10:25 and 10:35, in time for her brother-in-law and next-door neighbor, William Marshall, to pick her up. Marshall said he went to the station and waited about 30 minutes. When she did not show up, he said he left. Officials of Westinghouse Elevator Corp., which built the escalators and usually investigates accidents on them, said that they had not received complete details from Metro or District police officials. Metro officials said they would appoint a committee to look into the accident. About 60 percent of all Metro accidents occur on escalators, according to Metro officials. In 1988, there were 152 injuries reported on Metro escalators, stairs, platforms and mezzanines. Last year was the transit system's safest year; in the stations, there was an average of 1.2 injuries for each 1 million passengers. The accidents Friday and Monday raised anew the question of escalator safety. Two callers to The Washington Post yesterday claimed they were in recent accidents caused by escalators. The callers and Jo-Barbie Walker of Glen Burnie, who was injured Friday, expressed frustration that they do not know what to do in an emergency on an escalator. In an emergency situation, Metro officials prefer that riders contact the station manager, who has a key to turn the escalators off. If that is impossible, the escalators can be shut off by pressing emergency buttons at the base of the escalators. They also can be stopped by kicking the sidewalls at the top or bottom landings.