The body of a young woman, believed to have been strangled, was discovered early yesterday morning in a stairwell of the Old Post Office Pavilion about an hour after the crowd that had gathered in and outside the building for Washington's third annual New Year's celebration had dispersed.

The death and incidents of fighting and bottle throwing during the celebration prompted Mayor Marion Barry yesterday to ask the police department for a "complete report" on the night's events.

Police estimated that a crowd of 100,000 gathered for the evening of music and celebrating and to watch a 900-pound copy of the 1986 "LOVE" stamp descend at midnight from the Post Office Pavilion tower on Pennsylvania Ave.

Lt. William White, a police spokesman, said the 15 arrests made in connection with the gathering were not "excessive," considering the number of people, and he and other police officials described the crowd as well behaved. Barry said the city-sponsored celebration, dubbed "Putting on the Glitz in 1986," was "a very successful event for the third year in a row."

The body of the unidentified woman was discovered shortly after 2 a.m. in the southwest stairwell of the Old Post Office Pavilion's first floor by several celebrators.

The woman was taken to George Washington University Medical Center, where she was pronounced dead at 3 a.m. A preliminary autopsy yesterday showed the woman had been strangled, according to White.

Homicide investigators were still trying last night to identify the woman, who was wearing a turquoise-colored pantsuit, white blouse, gray felt ankle-high boots and a silver medallion around her neck and who was described as being in her twenties. The stairwell where she was found had not been used by the public during the event.

"I am very concerned about the death and the reports of other incidents and I've asked the police department for a complete report," Barry said in a statement. "Thousands of people from all over the region came downtown to bring in the new year together and have a good time. Only a few people at the end of the evening tried to spoil it and I regret any concerns this caused for those who had come down to celebrate."

Police said sporadic fights broke out in the crowd, resulting in 12 arrests for disorderly conduct. Rocks and bottles were thrown, resulting in one arrest and at least three people being treated for cuts in the George Washington emergency room. Police made two arrests of vendors who were selling items without a permit, and four persons reported they were robbed of their purse or wallet.

The outdoor concert was stopped several times when members of the audience began rushing the stage. Several people in the audience were injured during the shoving and were sent by ambulance to local hospitals. The injuries were not serious enough to require hospitalization, according to officials of the hospitals.

During soul singer James Brown's performance, police waded through the crowd to push people back from the stage fence. Several in the audience said police used their night sticks to force people to move back.

"If any such incidents or use of batons occurred, they will be discovered in our after-action review," White said. He explained that a review of police actions is done routinely after large events.

While city and police officials stressed the small number of arrests in terms of the thousands of people who turned out, several of the participants described the crowd as unruly and out of control.

"The crowd control, there wasn't any," said Michael R. Hooper, 22, of Silver Spring. "I know last year I went down there and had a really good time. This year it was totally outrageous. It was totally out of control."

Hooper, who said he was about 40 feet from the outdoor concert stage where most of the fighting took place, said groups of 30 to 40 youths locked arms and rushed forward during James Brown's performance.

"People were pushing you one way and you would get pushed another way. Then people would start throwing punches," he said.

White said sporadic fighting broke out "during the latter part of the activities, about 1 a.m."

City Council Chairman David A. Clarke said the 15 arrests were "not unusual for an event of 100,000 or 50,000 people." He said that while he was standing on the stage early yesterday morning a woman fainted in the front row and he helped carry her to an ambulance.

He said he could not make a judgment on the behavior of the crowd "based on just my two eyes" and said any changes in future celebrations would depend on the circumstances behind the strangling death and crowd-control problems.

Council member Nadine Winter (D-Ward 6), said the problems at the celebration have long been problems at other large gatherings, such as New York's annual celebration at Times Square. "You can have incidents anywhere," she said. "In other places where people gather, there could be dead bodies. You don't stop a basketball game or football game if someone gets hurt."

Metro spokeman Marilyn Dicus said the subway closed at 2 a.m. as scheduled without any major incidents. She estimated that half the New Year's crowd took the subway home. Crowds were so heavy at the Federal Triangle station that passengers were allowed to board the train free and pay when they got off, she said.

Police in the District and the suburbs concentrated their efforts on keeping drunk drivers off the roads -- apparently with some success.

A total of 1,167 drivers were stopped at a sobriety check point set up for five hours on U.S. Rte. 1 and Pinehill Street in Laurel by Prince George's County police. There was one arrest.

There were 24 arrests for drunk-driving violations in the District, 17 arrests in Fairfax County and 17 arrests in Mongtomery County. In addition, Maryland State Police made 43 arrests.