First-year Medical School students yesterday carried out the first step in a plan to force the return of pass-fail grading to the Med School.

A student representative said yesterday that more than four-fifths of the first-year class submitted examination books for a 90-minute midterm in Physiology which bore only numbers for identification.

The students are protesting a four-point grading system--excellent, pass, marginal and fail--which replaced a pass-fail system last spring.

"It was quite uneventful and there was very little acrimony. Wilson just handed out the test and people used the code numbers," the student representative, who asked to remain anonymous, said. The instructor in the course is Dr. Thomas H. Wilson, professor of Physiology.

The students have agreed that only those who fail the test will identify themselves if the numbers and grades are posted next week. They hope that the faculty will simply record "pass" marks for the remaining students, the representative said.

Numbers Game

The protesting students committed themselves to the plan at a meeting to draw numbers on Tuesday. The representative said yesterday that 151 of 162 first-year students signed that day, and at least 140 of them followed through at the exam.

Faculty response to the student protest is not clear. Neither Wilson nor Robert H. Ebert, dean of the Med School, was available for comment yesterday.

No Rebellion

The student representative reported that a group of students met with Ebert yesterday and that Ebert suggested the formation of a faculty group to talk with the students.

Frederick C. Lane, dean of Students, said yesterday that the protest was "not a rebellion."