A 20-year-old man pleaded guilty yesterday to second-degree murder in the strangling of a young woman during the city's New Year's Eve celebration at the Old Post Office Pavilion, saying he killed the woman after she repeatedly asked if he was homosexual.

Alex Tyrone Simmons told D.C. Superior Court Judge Robert Tignor that shortly before midnight he choked Marquita Vaughn, whom he had met that night, after Vaughn taunted him when he rebuffed her sexual advances.

"Was that what motivated your actions?" asked Tignor in the courtroom crowded with Simmons' friends, family and his clergyman. Simmons said it was.

Prosecutors agreed to drop a first-degree murder change in exchange for Simmons' guilty plea to second-degree murder.

Simmons stood quietly throughout yesterday's proceedings, listening as prosecutor Neil Hurley described how an evening of celebration and passion turned into a night of death for Vaughn, an 18-year-old from Northwest who was described by her family as a rebellious adventure seeker looking for adult freedoms.

Simmons, a Wheaton resident who had worked as a cashier in one of the restaurants at the pavilion, told the judge that Hurley had accurately described the evening's events, including that Simmons had sex with Vaughn after she was unconscious "to prove" himself.

Hurley said Simmons, who confessed to police two days after the murder, told police the two young people had been introduced earlier that evening by a mutual friend and later decided to leave the boisterous celebration for a more secluded stairwell.

There, Hurley said, Vaughn first kissed Simmons. When he did not respond, the young woman asked "what's wrong, are you gay?"

At that point, Hurley said Vaughn left for a moment but returned with her pants down. Once again, Simmons told police, he did not react when Vaughn kissed him.

Vaughn kept "bothering him and bothering him," Hurley said Simmons told police. When Vaughn again asked if he was gay, Hurley said Simmons grabbed Vaughn around the neck with both hands and began to strangle her.

Quoting Simmons' account to police, Hurley said Simmons could still hear Vaughn's taunts. So "in his own words, he proved himself by having sexual intercourse" with Vaughn as she was unconscious.

Flanked by his lawyer, Allie Sheffield of the public defender's office, Simmons responded "guilty" when Judge Tignor asked: "As to the offense of second-degree murder, the killing of Marquita Vaughn with malice and aforethought, how do you plead?"

Simmons can be sentenced to up to 15 years to life in prison. He is being held without bond, pending his April 21 sentencing.

Simmons has no previous police record, and at an earlier hearing he was described as a churchgoer and a graduate of the Duke Ellington School of the Arts, the D.C. schools' program for talented musicians and artists. Simmons had worked at Blossoms, a bar-restaurant in the pavilion.

The New Year's celebration at the pavilion has been an annual event for the last three years, as nearly 100,000 people have jammed together each year for the indoor and outdoor events at the renovated landmark. On the night Vaughn was killed, more than 300 District police officers were on duty in the area. Police described the violence, which also included fighting and bottle-throwing, as the worst in the three years the celebration has been held.