A look at educators who care - what makes them tick?

It is not yet clear how reforms being proposed by numerous national education studies (nine since last spring) will affect American schools. But on one thing they all agree: The teacher is the key link to improvement in education.

Teachers play varied and crucial roles. They load up their students with classwork; they teach ''Macbeth,'' computer programming, quadratic equations, and American history; they grade essays, chaperon dances, paste up yearbooks, and - proudly - attend graduations; and, through it all, they help young people understand why.

This is a report on a handful of excellent teachers and administrators at a suburban and at a city school. It's a report from both sides of the teacher's desk, because that's where this visiting reporter (also an accredited teacher) spent a week recently to get a firsthand look at good-quality teaching.

Although the schools are in New York State, classrooms like these can be found anywhere in the nation's more than 16,000 school districts.

Niskayuna High School has a suburban campus outside Schenectady, N.Y. It could never be confused with Benjamin N. Cardozo High School, in the Big Apple's borough of Queens. Niskayuna has some 1,375 students; most are white, and upper middle class. Clothes and hair styles are preppy. The school boasts one of the highest average SAT scores in the nation.

Cardozo, on the other hand, has 2,400 students, 45 percent of whom are black, Asian, or Hispanic. Big, urban, and proud, it is said to be the best general-attendance high school in New York City.

Karen Ludwig teaches a high school honors English class at Niskayuna. She has taught for 11 years. In class, it is apparent by the ease with which the Niskayuna students join in, that they expect to discuss topics of substance.

As she turns the class over to me, there are butterflies in my stomach. Don't let any teacher fool you. At that first meeting with a new group of students, especially when you know the kids are smart, you hope you belong there.

A teacher must ask: Will I help or hinder the curiosity that greets me? Will the students learn something? Will we communicate with each other? Or have the years set up some arbitrary wall between generations?

Today's lesson covers Joseph Conrad's novel ''Heart of Darkness,'' whose theme explores the conflict between good and evil as seen in the heart of one man. Discussion centers on whether there exists any standard of right and wrong higher than an individual's own choosing. Is situational ethics all there is?

It's not an easy subject to test, but it's one that must be taught. And, once taught, it will help students resolve this generation's big questions, such as those reflected in computer trespassing. There is inestimable value in sharing, even if only for a single class, the kind of work Karen Ludwig does; for scores of students, her English class makes ethical considerations - whether applied to computers or any other field - more familiar and more practical.

Every one of the nine current education studies highlights the deficiency in high school and college graduates' ability to communicate in writing. Each report emphasizes the need for students to write more during school and for homework.

At Cardozo, John Walsh teaches English. In fact, he has been teaching English in New York City schools for 23 years. What does he think of all the talk about education reform?

''When I see the teacher-student ratio decline in English classes, then I'll know people are serious about reform,'' he says.

Although his subject is English, the lesson for an outsider boils down to simple arithmetic. At Niskayuna, English classes average 25 students. Teaching five classes a day brings one into contact with 125 students. In New York City, the teacher contract allows for a class size of 34 students - 170 students in five classes. If Mr. Walsh gives just one writing assignment a week, asking students for a 150-word composition (''woefully in-adequate,'' he says), and spends only three minutes correcting each paper (''just as inadequate''), he must put in six to seven hours of grading - one extra day in an already full week. Mr. Walsh believes in going beyond the bare minimum. He assigns more than one essay a week, and invests the extra time required.

Sit down in any faculty lounge in any high school in the country and eventually you'll hear the topic of the principal surface in conversation. Is he in charge? Does he maintain order? Does he help or hinder learning?

Ed Carangelo's first supervisory position was as vice-principal of discipline at an all-boys' reform school. When push came to shove, everybody - student and faculty - knew the former Golden Gloves boxer would win.

At Niskayuna, Mr. Carangelo doesn't need such a skill. Here he displays a different kind of strength: Hall passes are required; order during the breaks between classes is routine but not regimented. Like a mother bear, Carangelo roams the school complex. His door is always open. He wants teachers and students to excel in whatever they do and they know he wants this for them.

Carangelo can name each student. Every fall he takes charge of a different freshman homeroom for a week, 20 minutes a day, until he covers every class. It's more than an impressive touch. What many teachers say the national studies on education seem to have forgotten is that schools are places where young people come together and meet adults. For many of the students, the face of authority, moral as well as disciplinary, is often the principal's.

At Cardozo, principal Bertram L. Linder, like some kindly uncle, takes care of the family. When one of his students or teachers succeeds, his pride isn't hidden: ''Well, of course! What did you expect?'' he says. ''We are good here.''

Mr. Linder has a more demanding task than Carangelo, when it comes to greeting students in the morning. His concern is geared not only to students, but to nonstudents who may try to slip into the building to disrupt things or possibly to sell drugs. Greeting the flood that pours in from the buses, Linder instinctively looks for any young person strolling in empty-handed. At Cardozo, every student has homework every night. Anybody without books is a target for special scrutiny from the principal or one of his assistants. There is a flood of immigrant children streaming into the United States in numbers similar to those of other ethnic groups at the turn of the century. When a principal opens the door for them, they see their new country's values of authority, equality, and opportunity in one very visible person.

Morning, gang!'' The greeting bubbles from the lips of teacher Rosemary Miner. She's speaking to her 24 tenth-grade students at Niskayuna. ''She's always glad to see us,'' a student whispers. Mrs. Miner knows her American presidents, and for 15 years she has been extolling their virtues and explaining their vices in American studies classes. If you had to choose one word to describe her teaching, the word would be enthusiasm. Today's lesson is on the role of a free press in a democracy. Mrs. Miner is a trouper, and she isn't going to let slip the opportunity presented by this visit from a representative of the fourth estate.

By the time the class is over, the fourth estate, too, has learned something that goes to the heart of the call for reform in teaching. If the United States is a ''Nation at Risk,'' as the President's Commission on Excellence says it is, it is just as important to have a teacher who is ''always glad to see us'' as it is have the top 25 percent of college graduates entering the teaching profession , as some states, and two science and math bills before Congress, propose.

It is crucial to have true scholars running our classrooms. But learning in schools occurs only when one can engage students. There is a mental climate in classrooms that transcends the academic. A teacher is constantly imparting the ideas, attitudes, and values that temper this mental climate. And a teacher who welcomes his or her work with students nurtures that climate. Students intuitively know it helps to have teaching done lov-ingly. That's why they are always glad to see Mrs. Miner, too.

At Cardozo, the Shakespeare lesson begins. Richard Brodsky is reading the knocking-at-the-gate scene from ''Macbeth.'' If the great Bard himself were a student in this junior English class, so inspired would he be by Mr. Brodsky that he would take the next subway to Broad-way. Brodsky's students experience the broadest possible world open to the imagination - and they learn. If anyone is looking for a definition of a teacher, he could find it just sitting in this class for a day or two.

Why is Richard Brodsky here in this inner-city classroom after 20 years' teaching experience? He appears too urbane for high school, but he is willing to put up with the knocking at his own classroom door by late students and students with special passes - with the crowded faculty lunchroom, where a brown-bag lunch, if not an economic necessity, is a gastronomic one; the daily attendance reports; the loudspeaker's interruptions - because he is dedicated to his calling.

Studies show the average age of US teachers is climbing. This statistic sinks in when you see it localized in two school buildings. The average age of the faculty at Niskayuna and Cardoza is 44 to 45. Very few of the teachers are in the range between 22 and 32.

Eventually, the older teachers will start retiring, and, when they do, somewhere and somehow experienced replacements will have to be found. Where they will come from is at this point uncertain. Society can no longer take for granted that talented individuals will automatically go into teaching. There are many other options open for them today.

It would be a great loss for students (and for prospective teachers) never to have Richard Brodsky reading them Shakespeare; or Rosemary Miner discussing the presidents; or John Walsh waging war over split infinitives; or Karen Ludwig ferreting out themes of good and evil in a Conrad novel. Each of these teachers wants the young to value ideas. More important, all of them have spent a lifetime sharing them.