Upgrading college teaching and learning. Schools focus on grad-student instruction. At most major colleges, freshman and sophomores take their courses not from professors, but from graduate students, many of whom do not know how to teach.

IT'S been a nettlesome problem in higher learning for a long time - but one that's now being addressed by universities across the country. The problem is graduate-student teachers. At most major colleges and research universities, freshman and sophomores take their introductory courses not from professors, but from graduate students, many of whom are only a few years older than they.

Traditionally, these student teachers are not given much systematic supervision or preparation for the classroom. Many are more interested in their own graduate work than in teaching. Furthermore, an influx of international students in graduate math and science means that in some schools classes are taught by teachers who don't speak English well.

The victims, say experts, are undergraduates who - ironically, they note - are paying much more tuition today for the experience.

``I find that graduate students don't know how to teach,'' says Sheldon Rothblatt, chairman of the history department at the University of California, Berkeley. ``They have to be watched: They are either too rigorous or not rigorous enough. They haven't much experience of life. Too often they find nothing nice to say to undergraduates - and much of knowing how to teach is knowing how to encourage.''

Eminent sociologist David Riesman, who supervised graduate-student teachers for years at Harvard, says that ``young people don't realize that sarcasm can wound somebody. My students couldn't believe, at first, how deeply some of their offhand remarks hurt class members.''

Some graduate students, especially at top colleges, are excellent teachers, experts say. But many are not. And small private colleges often sell themselves on the fact that entering freshman will not be subject to the Russian roulette of graduate-student teachers.

Rothblatt, Riesman, and others note that ``teacher assistants'' (TAs, as they are called) have been an important part of the structure of colleges since World War II and the advent of mass higher education. To teach most basic subjects - especially introductory courses in math, literature, writing, reading, foreign languages - small classes are needed. Faculty time is precious. Somebody has to do the job, and it falls on the TAs.

That isn't likely to change, say academics. What will change is TA preparation. ``We're going to have to be a lot more sensitive about it,'' says Rothblatt. Typically, college departments manage TAs. But as more attention is paid to freshman and sophomore matriculation, college administrators are taking a ``university responsibility'' to improve TA teaching, says Carol Cartright of Penn State. Dr. Cartright helped launch the ``Alliance for Undergraduate Education'' last month - 12 research universities that will examine their undergraduate education, including TAs. Late last month, Ohio State hosted the first national conference ever on improving graduate-student teaching. Colleges such as the University of Colorado (UC) have started new teaching courses for TAs. ``At a time when every college wants to retain its students, more attention is being paid to complaints in student exit interviews,'' says Prof. Mary Ann Shay of UC.

Most graduate students are ``content-competent'' says Dr. Mary Allen Gleason at Penn State, but they aren't comfortable in front of a class. They need help in moving from a student to a faculty role, and with the ``mechanics'' of teaching - how to stand, how to move.

Riesman feels solving the problem ``is really very simple.'' Pay ``sustained attention'' to it, he says. New night courses, seminars, and more faculty meetings on the subject indicate such attention may be more forthcoming.