Long-standing Time Warner Book Group chairman Larry Kirshbaum is stepping down.

Kirshbaum cited personal reasons for his departure in a memo released to staff on Monday morning. “I have been thinking for a long time about becoming an entrepreneur and turning to a smaller business (most likely as a literary agent) where I can work with authors in a more intimate way without all the stresses and strains of administering a large company.”

As publisher of last year’s John Stewart blockbuster, “America,” Warners had a robust 2004, with sales estimated at $465 million, up 9% from the previous year, according to Publishers Weekly.

But despite strong earnings in recent quarters, the announcement suggested more turmoil could be due the Time Warner division, which was put on the block and then withdrawn in 2003 after AOL failed to secure its $400 million asking price.

Kirshbaum, a prominent and affable book world figure who has been TWBG chairman since 1996, is credited with discovering “Bridges of Madison County” author Robert James Waller. He published Jack Welsh’s memoir, “Jack: Straight from the Gut,” for which the G.E. chief was paid a record advance of more than $7 million.

Kirshbaum wouldn’t be the first publisher to make the transition to agenting. Elaine Koster, who was president and publisher of Dutton and New American Library, now runs her own agency.

Earlier this month, L.A. Times Book Review editor Steve Wasserman announced he was leaving the paper to become a book agent at the New York firm Kneerim & Williams.