For five years, Thomas Collier has fought to halt a negative spiral of poor student discipline, low teacher morale and the breakdown in educational quality that plagues much of the District's public school system.

As Collier watched about 200 seventh-graders enter Paul Junior High School in Northwest Washington yesterday -- the first day of school for about 110,000 city students -- he said he hoped he could keep them "just as good and docile as they are right now."

Collier, 47, the father of four children who attended Paul, is the principal at the school, Eighth and Oglethorpe streets NW. And as principal Collier is the mediator, judge, parent, counselor, administrator and supreme answer man for the students, their parents and the school's 42 faculty members.

Students trickle inside in twos and threes, in crisp new blue jeans, sporting barrettes and double disco belts. Girls giggle, their hotcomb hairdos glistening, young boys chew on fingers and tease one another. Most pass through the doorways in awe.

They come from mostly black professional, middle-income families in the Northwest Washington communities of Petworth, Shepherd Park, North Portal Estates and Colonial Village. The area is bounded by Buchanan Street to the south, to the west by Rock Creek Park, to the north by the Silver Spring boundary line and to the east by Third Street.

These are seventh graders starting adolescence at a school new to many. Collier stands patiently inside the doorway -- friendly, but not too friendly.

"It's important for them to see the principal, but their relationship will be different from the one they had with the elementary school principal -- that was more parental," Collier said. "It's a weaning away from the principal's office, but we don't want to do it suddenly. It's important for them to see me and know that I am the authority here."

For many years, the D.C. public school system has been under attack from administrators, faculty and parents for what some see as a decline in the quality of education and the demise of general discipline.

At some high schools, students have graduated without being able to read. From time to time, students have scored in achievement tests lower than students across the country despite evidence that teachers here are paid some of the highest salaries and have more graduate degrees than those in comparable cities.

In some areas of the city, faculty and administrators, under pressure from parents, have called for more parental cooperation and involvement to remedy the ills.

D.C. Mayor Marion Barry said yesterday that he was concerned that many black families, who he called the backbone of Washington society, chose to take their children out of public schools rather than attempt to improve them.

Recently, for example, City Council Chairman Arrington Dixon took his two daughters out of Shepherd Elementary School, considered one of the city's best, and enrolled them in a private school.

Barry said the fact that the younger black middle class is taking children out of public schools poses a serious problem for the city.

"They are the infrastructure of our community . . . In our own community, you can't lose your middle-class support or involvement. Otherwise, your public schools go to the poor," Barry said.

Principal Collier said, "Some of the wealthier parents who can afford to send their children to private schools do so thinking the children will get a better education there.

"But in effect, they are raping the public schools of some of the more motivated students, and that has a negative effect because students need peer motivation. Paul has been affected by that."

The problems of the District school system became more acute this year after a 23-day teachers' strike.

At Paul Junior High, however, some parents say one man is beginning to make a difference in turning a negative atmosphere into a positive one. They credit Thomas Collier.

"Paul Junior High has been suffering from a bad reputation," said Mary Brunson, former PTA president who is still active in the school. "There was dope, there was stealing, all of that stuff was running freely there and we had gang fights all the time.

"Before, students had no respect for the administration" Brunson said. "They used to yell names at the former principal, but Mr. Collier has changed all that. He speaks to the children nicely and firmly and they understand he means just what he says.

"I used to be afraid of sending my children there," said Joyce Taylor, another parent. "There were kids coming in who didn't belong and I used to go to school with other parents to help patrol the halls, trying to keep kids in classes. Now, under Mr. Collier it seems like everything is up to par."

Keeping things up to par requires the ability to juggle different roles, Collier said. On the one hand, he has to convince reluctant teachers that school Supt. Vincent Reed's Competency Based Curriculum plan is a good way to make sure that students do not graduate wihout the basic reading - writing - arithmetic. Skills needed to compete in society. CBC uses a step-by-step manual for teachers for each subject.

"Some teachers resent the extensive testing. Some teachers don't think it's meaningful enough, but I don't know of any other way to evaluate a school to see if it's doing what it should be doing," Collier said.

On the other hand, he has to accomplish the goal of education with less authority than his predecessors wielded in bringing both students and teachers under control.

He cites a decree issued by the late U.S. District Court Judge Joseph Waddy in 1972 that established lengthy disciplinary procedures to expel students; a student's bill of rights passed by the school board outlining students' rights regarding suspension, dress codes and other matters, and restrictions from the teachers' union which requires grievance proceedings.

"In the old days, a principal was the supreme authority figure, feared by students and teachers, and he could walk a student to the sidewalk and say 'Don't come back.'

"There were some abuses of that authority, and that's why there were changes," Collier said. "Today, there is no such thing as expelling a kid from school unless he commits an atrocious violent act.

"But there are some problems in the schools that can be better handled by principals alone," he said. "And, if principals make bad decisions, they should be removed. We should be able to deal with problems of teacher performance or discipline right here."

His community is steeped in the get-ahead ethic. Collier said he and his wife, Edwardina, a public school reading specialist, persuaded one daughter, Cicely, now a corporation counsel to the D.C. Board of Elections and Ethics, to attend law school rather than seek a graduate English degree.

Another son, Thomas, who wanted to be a journalist, was persuaded to attend law school and now is an attorney with the U.S. Justice Department.

A second daughter is attending medical school. Their youngest child, 14, attends parochial school because Collier said she had trouble attending the same school where her father was principal.

"Like many other parents in this community, we expected our children to go to college," Collier said. "We felt that with the increase in opportunities for blacks and women, we wanted our children to be more independent financially. We would be typical of the neighborhood."

Also contributing to this story was Staff Writer Milton Coleman .