The 18-year-old, hearing impaired daughter of a Mexican diplomat, who family members said had been frustrated by her handicap and troubled by an argument with a classmate, yesterday took her interpreter at Rockville High School hostage at knife point for three hours.

More than 20 Montgomery County police, including an officer fluent in sign language, swarmed through the school while Alicia (Lilee) Vallarta and her 39-year-old interpreter, Cheryl Lee of Capitol Heights, were locked in a second-floor conference room. Police negotiators shouted through the door of the office and used sign language through the office window to convince Vallarta to surrender peacefully. No one was injured during the episode.

The girl's mother, also named Alicia, appeared upset by the episode. "She must be quite unhappy and dying to be heard," Mrs. Vallarta said. "But I hope she doesn't like all the publicity. I hope she doesn't start cutting out the newspaper articles for her scrapbook. I hope she doesn't like all the attention. I will tell her, 'Yes, you kept your father out of work all day, and yes, you kept your mother from making her dessert but this is not the way to get attention."

The mother also expressed concern for her daughter's problems. "Fortunately and thank God, Lilee hasn't hurt anyone and we're going to get her therapy. We want to help Lilee," she said yesterday at her home after hearing on the radio that the three-hour incident had ended quietly. "Any mother has trouble communicating with an 18-year-old. There is so much less communication with a deaf young girl. They have less ability to communicate their fears."

The daughter had been troubled lately, according to Mrs. Vallarta, who spoke of the girl's frustrations as she tries to communicate in a world made more complex by her disability and more confusing by the diplomatic life of moving frequently through different cultures in foreign countries. Her father is Jose L. Vallarta, an alternate representative from Mexico to the Organization of American States here.

Sitting in a wing chair in the elegant living room of the family's Rockville townhouse, Mrs. Vallarta said she had been scheduled to meet this morning with her daughter's counselor and an assistant school principal about recent problems at school. Following yesterday's incident, the family agreed to remove their daughter from the school and to seek counseling help for her.

"She had been having lately a lot of trouble with the group," the mother said. "Her teacher called me last night about a fight over class pictures. I said, 'Can't they work it out? I have 15 people coming to a dinner party. It's a bad day for me to go to the school.' "

Despite the scheduling problem, Mrs. Vallarta said she agreed to go to the meeting because it seemed so important to Lilee. During the family's frequent moves -- including assignments in New York, Switzerland and Washington -- the daughter has rejected various therapists, Mrs. Vallarta said. One of the therapists told her the teen-ager, who looks much younger than 18, "is functioning emotionally as a 10-year old," she added.

According to Gary Hotto, a counselor at the International Model Secondary School for the Deaf of Gallaudet College, hearing-impaired youngsters have the same needs and anxieties of other teen-agers but because they can not easily explain their feelings, they often are more frustrated.

"The willingness of those around them to meet their need to communicate is paramount. It's not the method -- signing or lip reading or what have you -- so much as the attempt. Sometimes the effort itself is enough because it can mean acceptance and acceptance is very important to the hearing impaired," Hotto said.

Returning from the school with her father, Lilee was laughing and eager to tell a reporter her side of the story. She said her friend gave her the small kitchen knife. But her father hushed her in mid-sentence.

He said he wanted to thank the police and school officials for their handling of the incident. But he said he thought the sight of so many police frightened his daughter who had asked to talk with the school counselor about her disagreements with other hearing-impaired children at the school.

"I don't think the police overreacted. They took all the necessary precautions because they didn't know how dangerous my daughter is. I know my daughter is not dangerous but they did not," he said.

Because the student is the daughter of a diplomat, she enjoys diplomatic immunity from prosecution in the United States and will not be charged in the incident, police said.

During the three-hour episode, police closed off the school wing where the two were locked in a suite of four rooms used for special education classes. To the apparent dismay of other students, classes in the rest of the building went on undisturbed.

The interpreter Lee, who police described as "somewhat emotional" after the ordeal, works regularly with Vallarta, helping her understand what is being said in classes and communicate through sign language. Lee declined to discuss the experience yesterday.