Second- and third-year Law School students began for the first time last week a new winter term during which they take one intensive course for four weeks.

Law students and administrators yesterday said the new calendar--under which second- and third-year students take exams before Christmas vacation--has led to several minor problems, but that it is too early to tell whether the short winter term will prove a valuable innovation.

Most of the upper-class law students will take one course five days a week during January and an exam at the end of the month.

Administrators felt that intense involvement in one subject would benefit students and add flexibility to their programs, Robert E. Keeton, associate dean of the Law School, said yesterday. He added, however, that some subjects adapt more easily than others to the concentrated format.

Concentrating on one subject will benefit those students who have found professors and courses which excite them, William J. Kayatta, a third-year law student, said yesterday.

Albert M. Sacks, dean of the Law School, said yesterday he plans to review the new calendar after the end of the winter term. "Some students might not be getting enough time to absorb the material in concentrated courses," he said.

"If you miss one class, it's like missing a week," Bradley S. Bridge, a third-year law student, said yesterday.

About 25 students, chosen by a faculty committee, are instead spending the winter term working on papers, Sacks said.

Others will participate in a special workshop on trial advocacy, in which they will spend up to seven hours a day working with lawyers and judges to simulate trials, Keeton said.

The new schedule does not affect first-year law students, who will take their exams in January as in the past.

"The faculty felt it was important to give 'One Ls' the time to percolate," Mary D. Upton, assistant dean and registrar of the 'law school, said yesterday.

Kayatta said that first-year students would benefit most from the schedule change, since they are the ones who worry most about exams during vacation.

"The calendar is not doing what it's supposed to do," he said.

Upton said there were no plans to extend the new calendar to first-year students.

Some students who spent time in the fall interviewing with law firms found the earlier exams "very disruptive," Michael A. Clark, a third-year law student, said yesterday.

"I heard complaints in December from 'students who were unhappy about taking exams then, but the ones I've spoken to said they had great vacations," Keeton, who was an advocate of the revised calendar, said.