Near the end of a teacher workshop at Martin Luther King School in Beltsville, a group of teachers tried to describe why the 12- to-14-year-old child is the terror of teachers.

"Two hundred percent energy," said the English teacher.

"Immaturity--they're always changing," said the gym teacher.

"Wide swings in emotion, too," a third teacher chimed in.

"It's like them being 13 going on 30," said Helen Green, who has been teaching English for 15 years.

Because county school Superintendent Edward J. Feeney feels that from the top of their still developing brains to the bottom of their growing feet, the preadolescents need special care, Prince George's County is converting its junior high schools to middle schools.

Martin Luther King this year became the 17th building in the system to make the switch from a building for seventh, eighth and ninth graders, to one for seventh and eighth graders only. Under a policy approved by the school board in 1981, all but two of the county's traditional junior highs will be phased out by 1985.

In committing the county to the concept, Feeney joined a movement that has spread to about two-thirds of the public school systems in America. The idea behind middle schools, developed in the 1950s, is the elimination of peer group and other pressures on adolescents to act like 18-year-olds--especially socially--before they reach 14.

In Prince George's, the coming of the middle school has meant:

Removing strict course and schedule requirements imposed by most states on ninth graders as a condition for high school graduation.

Retraining teachers in the unique stage of cognitive and emotional maturity of the 12- to 14-year-old. Researchers maintain that the middle school years coincide with a pause in brain growth, possibly indicating a need to reinforce thinking skills already acquired--like study habits--rather than forcing new ones.

Organizing students into groups of 150 to 250 students all taught by one team of teachers in individual subject areas.

Flexible scheduling to create large blocks of time for core subjects such as English and social studies as well as teacher planning.

The conversion to middle schools in larger school systems was slowed by a lack of capacity in senior highs, but with the end of the baby boom, space is opening up in many senior highs for a ninth grade.

Despite ardent support from many educators, the benefits of middle schools are still subject to debate in the profession, especially in these days of budget crunches, because per-pupil costs are higher for students in high schools than in junior highs. And some eighth graders caught in the transition from what was almost high school to, in effect, an advanced elementary school, also have their reservations.

"In junior high school you could do everything," said eighth grader Erik Harrison. "It's like jail," he added about the more structured middle school environment.

The 833 students at Martin Luther King are divided into three teams, one for each grade and one combination team for seventh and eighth grades. Within each team there are six to 10 home room groups who move together from one 42-minute "module" (subject class) to the next.

They move, usually accompanied by their teachers, without benefit of a bell or buzzer and without the normal helter-skelter surge into the hallways. The home room group follows a complicated schedule that changes every other day and features 84-minute periods for subjects such as English and study skills, as well as physical education.

But eighth graders complained in interviews that their biggest gripe is that middle school has put a large dent in their budding social lives.

"Last year we could walk in the halls and go to the dances; this year there are assigned seats for lunch and no dances," Harrison said.

"When we had dances we had a real disc jockey; the lights were low . . . ," recalled 13-year-old Andy Smith.

PTA president Tema Kelly said that she would not like to see a rerun of the five or six dances the school had last year. They were similar to the ones she attended growing up in Montgomery County, except that in her son's school, "there was a lot more going on," she said. "The girls were dressed like they were 20 years old and the boys were trying to act accordingly."

Instead of the dances, Kelly is planning a "family night" for February, featuring brighter lights, perhaps a ping-pong tournament, square dancing--and parents. She is worried that the students may not line up for the affair.

"Kids at this age just don't want to do things with their parents," Kelly said. "It's a whole question of keeping the family unit together. We're going to give it a shot, though." Students say they are making up for lost dances with house parties.

Despite the middle school desire to slow the rush to teendom, some things are still the same at Martin Luther King. The girls are still a head taller than the boys and the heads are usually curled and coiffed for maximum effect. By the end of the seventh grade, about age 13, the undersized males will begin to notice the differences and nothing will remain the same, according to math teacher Elma Edwards.

"They learn it from older brothers and sisters," said Edwards, a 14-year teacher who is very high on the middle school approach. "Parents can control some of it, but how can you tell a girl she can't dress up and wear designer jeans?" she asked.

School principal Jean Mills points to some successes at Martin Luther King: Discipline problems have declined and the infractions are less severe, Mills said, and there has been a sharp increase the number of parent-teacher conferences that can be scheduled in a day.

Those periods are also used for teaching team discussions of individual student problems, another unique middle-school feature.

"Say I'm acting up in one class," said student government president Steve Phipps, 13. "All the teachers can get together and find out why I'm doing it. I think it's a good idea myself: It helps students academically because they know that all their teachers know what they are doing,." said Phipps, who also noted that his friends are having a lot more house parties this year to make up for the lost dances.

Despite the the possible benefits of the middle school philosophy, other area school systems have no plans to change the basic thrust of the junior high school.

Seventh and eighth graders in Fairfax and Arlington counties attend so-called "intermediate schools," and eight of Montgomery's 21 mid-level schools group those ages together. But school administrators in those areas said the shifts were made more to fit the patterns of declining enrollment, than in an attempt to shift the basic philosophy of the schools toward the elementary and away from high school.

Montgomery had some sixth-through-eighth-grade middle schools in the late 1970s, but the school board since then has has been cool to middle schools, in part because some beloved elementary schools faced closing because of the loss of their sixth graders.

Yet fast-growing Howard County has been all-middle school since 1966, largely due to the efforts of James Di Virgilio, who is in charge of middle schools there and president of the Maryland Middle School Association.

Di Virgilio cites a steady rise in test scores in their 11 schools as evidence that the concept works. And after several crops of middle school graduates, Di Virgilio states with pride that Howard eighth graders are "not as sophisticated, not as worldly wise" as their counterparts in junior high schools.

Di Virgilio, perhaps Maryland's foremost believer in the middle school approach, gave Prince George's high marks on its commitment to the conversion. But other area school administrators remain skeptical about the value of the concept.

"It's not necessarily a panacea," said James Guines, an associate school superintendent in the District who set up a middle school program in Richmond in 1970. "There are bad middle schools and there are bad junior high schools. There are good middle schools and good junior high schools."