A 12-year-old girl, whose account of being raped last week by an intruder in a Southeast elementary school bathroom unleashed a wave of community concern, admitted yesterday she fabricated the story, D.C. police said.

Lt. Eric Mines of the police sex squad said police yesterday concluded their investigation of the Sept. 13 incident "and it was revealed that she did not encounter a man in the restroom and that she was not raped."

"The imagination of a young kid is unlimited," Mines said in response to questions from reporters at an impromptu press conference at police headquarters. "There was no gun . . . . Nothing happened in the bathroom."

The girl had told authorities she was struck on the back of the head by an armed man who jumped her on her way to a basement restroom during school lunch period. She said she was gagged and then raped.

Medical reports from D.C. General Hospital, where the girl was taken immediately after the reported rape, failed to support her story, Mines said, adding that other "inconsistencies" arose, which he would not describe.

Mines said police spent "countless hours" questioning students, teachers and others. "Let me assure you that she was not coerced in any way," he said, "There was a lot of time and a lot of patience put into this investigation, and the mother was given a chance to participate in this investigation, and did."

Mines would not comment when asked why the girl would have concocted the story.

D.C. Schools Superintendent Floretta McKenzie, informed of the girl's admission in a 3 p.m. telephone call from Police Chief Maurice T. Turner, held a news conference yesterday afternoon and said: "We are very glad and relieved that such a serious incident did not happen, and we certainly regret all the anguish that the schools, the parents, the teachers, and everyone experienced as a result.

"However," she continued, "This doesn't diminish our need to pay attention to security, to make it a top priority, and we will continue all of these efforts in that area."

The reported rape outraged parents and neighbors near the Anacostia school, and more than 400 people turned out at a meeting last week organized by concerned parents who outlined ways for the community to beef up security at the school.

The rape report also touched off what school officials termed a case of mass hysteria in which youngsters at Walker-Jones Elementary School in Northwest claimed last Wednesday that a man dressed as a woman chased them in and around the school. Anxious parents withdrew more than 100 children from the school within a two-hour period.

Shelton Lee, director of safety and security for the school system, said yesterday that disclosure of the fabrication does not alter plans to shift six employes to security duty and hire 12 more once the new fiscal year starts next month. The security staff will then total 98, he said.

"I am proceeding on the premise that it could have happened, even if it didn't," Lee said of the rape report, "If we were to slack now, we would open the door for this type of thing."

As a result of the incident, he said, "We have a shot in the arm in terms of sensitivity and awareness in the community that people have to be involved in security. I was out there at [the Southeast school] this morning and they had parents at every entrance to the school and four or five outside."

The school's principal said yesterday she doesn't think her school will ever be the same, but said some of the changes have been good. She said the incident prompted many parents to become involved in their children's school for the first time.

"The incident has pointed up some things to schools and the community in general that might, indeed, help our kids be more safe in schools and in their homes in our community," she said. "We just can't think about protecting our children when a crisis occurs.

The principal also said she is deeply concerned about the 12-year-old. "Fabricated or not fabricated, something traumatic must have happened to that youngster," she said, "I don't believe a 12-year-old would maliciously make up a story like that. Someone would have to do an awful lot to convince me of that."