The Planning Office is studying a proposal to build a major underground addition to the Harvard Library system in the space between Widener, Lamont, and Houghton libraries.

Library officials hope the study will show the feasibility of building a four-level, 850,000 volume extension--which would relieve the need for more library space for another 13 to 15 years.

All plans are contingent on the study. No one at this time can estimate the cost of the extension. The study might find that it is impossible to dig deep enough for four levels. No date has been set for the completion of the study.

Construction will undoubtedly cause some "havoc" in the Yard, Arthur D. Trottenberg, assistant dean of the Faculty, said yesterday, "but nothing" we couldn't put back together again."

Trottenberg said the extension will probably have entrances from the basement of all three surrounding libraries--Widener, Lamont and Houghton.

The decision to study an underground extension comes in response to the library system's most critical space shortage since the 1930's. Widener was reported last year to be approaching the 85 per cent capacity point. That is the "danger point" for classified collections, such as Widener's, which must keep space open on all shelves for new additions.

A study of the problem was made last year and its report, calling for new additions such as this one, was presented to President Pusey last Spring.

This study did not mention the possibility of an underground addition but did list several possible sites for a new library building, including:

-- The land between Widener and Matthews Hall. This would force the elimination of Weld Hall.

-- The Yard sites currently occupied by Hunt Hall or Robinson hall. The Graduate School of Design, which now uses the buildings, will eventually move to new facilities on Quincy St. opposite Memorial Hall.

-- The block bounded by Massachusetts Ave., Plympton, Bow and Arrow Streets across from Lamont.

-- Part of the block of land directly across Mass Ave. from Widener, including the University Restaurant and Bob Slate's.

All of these proposals are highly tentative, library officials emphasize, and the University isn't committed to any one of them.

In his annual report, Pusy mentioned new library space as one of the important priority projects on the University's schedule.

When the space problem arose in the 30's, a study was made that eventually resulted in the construction of Houghton, the New England Deposit Library, and Lamont.