Harvard added about 160,000 volumes to its almost 11-million-volume library system last year Or, to put it another way, assuming that the average book is about an inch wide, Harvard added about two and a half shelf-miles of books to the University Library.

Last year was hardly a profligate year for book-buying--in fact, the library has grown about two miles every year for the last decade. And that vast growth is posing severe problems for a system already light for space and pressed for adequate cash.

"We, at Harvard, are almost alone in this country in the potentiality for guarding out cultural heritage in our books," says Oscar Handlin, Loeb University Professor and former director of the University Library, "so that the responsibility affects not only this institution but the national scholarly community as a whole."

That powerful sense of mission poses certain imperatives for the system, and while the University's commitment to maintaining the best possible scholarly library insures that the Faculty of Arts and Sciences and other faculties are generous to the system, it also places a heavy responsibility on its managers.

"We're blessed with a tremendous heritage," agrees Yen-Tsau Feng, who, as Larsen Librarian of Harvard College, is the University official perhaps most intimately involved with the day-to-day problems of running the system. "We have inherited a lot, but that poses a burden because we have to keep it up."

Harvard's library, which employs about 13 specialists in different areas who determine which books will be purchased, operates according to three basic principles, Feng says: to build on the system's strengths, to collect in response to curriculum needs, and to recognize "the broad scope of human knowledge that any self-respecting institution should be committed to."

But at the same time, "Research needs are not a matter of current interest," she says, noting that Harvard seeks not only to add books which are needed now, but books that might not be needed until 50 years from now. "I always like to use a phrase that's a Chinese expression: learning is like sailing against the tide--if you don't advance, you're retreating," Feng says.

The two fundamental problems confronting Harvard's library fall into two categories: space and preservation. Space poses a problem because it can restrict Harvard's ability to stay on the vanguard of scholarship, and preservation because once those books are acquired, they begin to deteriorate on the shelves.

In Widener Library alone, librarians are struggling to find room for the 50,000 volumes added each year to the 66-year-old centerpiece of the system. At three million volumes--already stretching the limits of Widener's capacity--the building holds about half of the Harvard College Library, which makes up more than 40 percent of the whole University system.

Widener is constantly readjusting its collection to squeeze out more space, but officials are considering three major plans to create a long-term solution to the space crisis.

* Compact shelving, which involves installing new hardware. Stacks are put on rollers with just enough maneuvering room to permit access to one-stack at a time. The Law School's 1.4 million volume Langdell Library has been able to install compact, shelving successfully and came the burden there, as has the 160,000 volume Tozzer Library in the Peabody Museum.

But compact shelving is impossible in much of the Harvard College Library, first because the shelves in Widener act as supports for the floors above them, and in other cases, because the structures can't take any more weight.

* Miniaturization, which involves microfilming old books and buying new collections on film. Harvard already does some microfilming and purchases new volumes it doesn't have in paper form. But while it can ease the space crunch, microfilming also demands new space for reading rooms and film viewers. And, says Feng, "not everything is conducive to or a good candidate for microfilming."

* Warehousing books somewhere outside Cambridge, which is the most radical and currently least feasible option. With costs much lower 15 or 20 miles away, a remote storage building would greatly cut expenses over the long haul, but require a large initial cost which the library may not be able to afford right now.

In addition, remote storage would mean adding messengers and more staff to a system which now employs 200 professionals and $26 support personnel in Boston, Cambridge, Washington--for the Dumbarton Gultz library--and Florence, Italy, site of Harvard's Vilin I. Tatti Renaissance studies center.