Henry Kissinger caused a stir in the literary world five years ago when he announced his memoirs would consist of two volumes because one book wasn't big enough to contain his saga. Time Inc. and its subsidiaries--Little, Brown , Book-of-the-Month Club and Time magazine--paid almost $3 million to Kissinger, and the initial volume, White House Years, sold well after its publication in the autumn of 1979 despite its formidable price ($22.50) and bulk (1,521 pages, 4.2 pounds).

But Kissinger is now expanding his memoirs to three volumes.

"Volume two will stop at Nixon's resignation," confirms Chris Vick, Kissinger's personal secretary who followed him into private life from the State Department. Offering a journalistic helping hand on both books has been Harold Evans, editor of the Sunday Times of London.

Originally, Kissinger said his first volume would cover his tenure as Richard Nixon's national security adviser, while a second book would deal with his years as secretary of state.

White House Years offered Kissinger's view of the world up to 1973. But instead of wrapping up his government years in a second book, Kissinger now has another tome on his hands--about 1,400 pages, says Vick--that doesn't begin to chronicle Gerald Ford's presidency. Now Kissinger's second book will encompass only part of his term as secretary of state as well as Nixon's troubled last year-and-a-half in office. The second book is due out this spring, the third in a couple of years.

Some critics suggest this allows Kissinger to use his 1983 "secretary of state memoir" to answer harsh books about his conduct of foreign policy expected in the next two years.

Not so, responds Vick. When the second book reached 1,400 pages, Vick says it became obvious that adequately binding any larger a book presented a technical problem. Thus the decision to write a third book.

Word of Kissinger's fecundity was news to Seymour Hersh, the ex-New York Times reporter working on an unflattering bood about Kissinger. "I dread having to read all that," he said wryly. "But I will."

Kissinger's publishers are betting a bundle that Hersh won't be the only one.