In the drab ninth-floor courtroom of the Suffolk County court house, everyone waits for question number 16.

When question number 16 comes, the attorneys lean forward, the gallery stirs, and the reporters pick up their pens. And then Judge James P. McGuire leans back in his chair, turns toward the prospective juror, and asks, "Do you have an opinion as to whether or not all abortions are wrong?"

Everyone waits for question number 16 because abortion is at the center of the manslaughter trial of Dr. Kenneth C. Edelin.

The Edelin trial--or, as it has come to be known, "abortion trial" --began this week in Boston, and after 69 prospective jurors trooped through McGuire's court during three days of jury selection, the judge had finally seated a 16-member jury.

About one-third of those who were rejected got hung up on the nettlesome question number 16, apparently for displaying toounwavering personal opinions for or against--but usually against--legalized abortion.

Edelin's indictment springs from an abortion he performed in October 1973 as chief resident in obstetrics and gynecology at the Boston City Hospital.

The prosecution alleges that the fetus was between 24 and 28 weeks old, and that the type of abortion Edelin was performing--by incision through the abdomen--should have resulted in the delivery of a baby boy.

The case has drawn national attention because it is likely to set precedents ih laws concerning abortion. The central issues are just when a fetus becomes a human being, and whether a doctor should be allowed to exercise his own judgement freely in considering whether an abortion should be performed. Testimony in the trial might also focus on the right of a pregnant woman to decide the fate of the fetus inside her.

During the next month, the jurors may have to consider all those questions--but for this week, question number 16 was enough.