A D.C. Superior Court jury has ordered the District to pay $250,000 in damages to a teen-ager who was lured out of an unsupervised elementary school classroom and sexually assaulted when she was 10 years old.

The girl, now 15, took the witness stand last week and told how a man came to a classroom at Mary Plummer Elementary School in Southeast Washington and said he was going to report her to the principal, according to her attorney, Patrick Christmas.

When she followed him into the hall to beg him not to report her, the man threatened her with a knife, began to choke her, then dragged her out of the school to nearby woods and raped her, Christmas said.

"I argued that the District, through its absolute carelessness and negligence, took away her childhood, and it was time to give something back," Christmas said yesterday. "She has dreams about things a little girl shouldn't have to dream about."

The jury's verdict Monday ended a week-long trial of the civil damage suit Christmas had filed against the D.C. government, charging negligence.

Christmas said he argued that the school was in a high-crime neighborhood and had previously been the site of crimes, including a purse-snatching and the robbery of a 12-year-old in 1976.

A playground gate was open and unlocked, and one of the school's back doors was broken and did not close properly on Sept. 20, 1979, when the assault occurred, he charged. Security, he argued, was not adequate to prevent the assault, the type of incident school officials could have foreseen.

Police investigated, but no one has been charged in the crime, Christmas said. School officials did not dispute that the girl was assaulted.

In documents filed in court, lawyers for the city denied any negligence. Yesterday, Assistant Corporation Counsel Johnny M. Howard, who represented the city at the trial, refused to comment on the case.

George Margolies, the school system's legal counsel, said yesterday that the incident "was not foreseeable." Margolies acknowledged that the back door "was not working properly," but said schools cannot chain or otherwise lock defective doors because of fire and building code regulations.

"You cannot absolutely prevent every type of incident unless you make a building so secure it is an armed camp," Margolies added. "Obviously, it the assault is a tragic incident we wish did not take place."

Christmas said the girl, a fourth-grader at the time, was asked to watch over a second-grade class while the teacher went to the school's book room.

The girl was writing on the blackboard when the man, a stranger, came in and said he was going to report her for standing up in class, Christmas said.

After the assault in Fort Chapin Park, which is behind the school at Texas and C streets in Southeast, the girl fled and ran back to the school, he said.

Edgar B. Dews, the school system's security director, said yesterday that in 1979 he had only four investigators to address "day-to-day security" in the entire school system. Assignments of community aides, who were used in schools for security purposes, were not controlled by his office. He said he conducted "awareness programs" on preventive measures for school personnel.

Now, according to Shelton Lee, the system's director of safety and security, 130 aides are assigned to the city's 170 school buildings and security measures have been greatly enhanced. Police also have increased surveillance of schools.