L. Don Leet, professor of Geology and the University's earthquake expert, called yesterday's early morning tremor "moderate in intensity" and said that it was part of a "pattern" which may bring a major quake to the northeastern U.S. "within twenty-five or fifty years."

Most of the Harvard community was asleep at 6:40 a.m. yesterday when, in the words of one early morning riser, "the ground shook slightly and there was a low rumble." Nearer the center of the shock, some 100 miles to the northeast of Cambridge, buildings swayed and china rattled for several seconds. There was little actual damage anywhere, however.

Leet, who spent yesterday at the University's Seismological Center in Harvard, Mass., said that he was "having a friendly argument" with seismologists at the Weston Observatory as to just where the quake's center was. Leet's calculation placed it in the Ossippee mountains of New Hampshire, while the Weston Center put it out at sea just east of Yarmouth, Maine.

Leet felt that yesterday's tremor was "a sort of repeat" of "the Ossippee quakes of 1940," which he described as "somewhat larger than this one."

Leet reviewed New England's earthquake history since 1755, the year of the last really severe shock in the area. For 100 years after this, he said, New England had no quakes of any consequence. Between 1850 and 1900 two "moderate shocks" were experienced.

Since 1900 "we have been having quakes more and more frequently," according to Leet. At present, quakes of the "moderate" variety seem to be spaced at about five-year intervals. "All in all, I think the Northeast is getting set up for another big one like 1755," he asserted.

Weston scientists blamed yesterday's tremor on "some breakage in the earth's surface." Leet said that the Northeast has nothing comparable to the celebrated "San Andreas fault," which has been the cause of numerous spectacular earthquakes in the Pacific coast area.