A Harvard professor who refused to answer question before a Boston grand jury, and was then dismissed by the government prosecutor, has again been subpoenaed to appear before the jury.

Samuel L. Popkin, assistant professor of Government, received notice Wednesday from federal agents that he must again submit to questioning by the jury which is investigating Daniel Ellsberg '52 and the Pentagon papers leak. He will appear next Wednesday.

The second subpoena came on the heels of a ruling Monday by federal judge W. Arthur Garrity ordering Leonard Rodberg, an administrative aid to Sen. Mike Gravel, (D-Ala.) and Richard Falk, Milbank Professor of International Law at Princeton, to testify before the jury.

Rodberg and Falk had argued Sept. 10 that confidential association necessarily prevented them from testifying. Rodberg claimed legislative immunity: Falk cited academic freedom and his connection with various publications. Although Rodberg was exempted from discussing actual Congressional business, the ruling was seen as a victory for those who advocate increased investigative power for the grand jury.

When first subpoenaed last August, Popkin attempted to quash the order by means of a similar argument. He contended that in keeping with the "Caldwell principle," his academic contacts with Ellsberg, an M.I.T. research associate, should be kept private. Earl Caldwell is a New York Times reporter whom a federal court recently excused from grand jury testimony, allowing him to protect confidential sources.

Judge Garrity denied Popkin's motion, ordering him to appear before the grand jury. After declining to answer the first three questions--"Do you know Daniel Ellsberg?", "Do you read the New York Times?" and "What Boston publications do you read?"--he was released from further testimony.

Under standard procedure, if a grand jury witness refuses to answer questions, he can be dismissed. Or he may be granted immunity from prosecution and then imprisoned for the duration of the jury's life if he still does not answer.

At the time of Popkin's dismissal, several observes suggested that the government's action constituted an admission that they themselves did not know what they wanted to find out from Popkin, and that they were engaged in a "fishing expedition" to obtain evidence.

Following this line of reasoning, Popkin has been subpoenaed for a second time because government prosecutors have now discovered which questions they might profitably put to him.

William P. Homans Jr., Popkin's lawyer, last night suggested an additional rationale for the second subpoena: following the ruling on Rodberg and Falk, the government can now proceed undaunted in its efforts to widen the jury's scope and power.

As of last night, Popkin apparently had not decided how he would treat the grand jury subpoena