Howard Kaminsky, the hard-charging publisher of Random House and heir apparent to its chairman and president, Robert Bernstein, abruptly resigned yesterday over what the company called "management differences."

Joni Evans, the former president of Simon and Schuster's trade books division, was appointed only hours later to succeed Kaminsky as executive vice president and publisher of Random House, just seven weeks after she joined the company to develop her own line of books.

Bernstein said of Kaminsky, who joined Random House three years ago after making Warner Books a major contender in trade publishing, "We've had differences, and as these things do, the differences matured." Kaminsky said of Bernstein, "There was a philosophical difference and I lost." Neither executive would discuss whatever may have divided them.

In her new position, Evans will be responsible for Random House and Villard trade books, but not for Times Books, Vintage Books and Fodor Books. Those three divisions, which reported to Kaminsky, now will report directly to Bernstein.

When she was offered her new job, Evans had just opened temporary offices for her still-unnamed imprint and hired an associate publisher, Susan Kamil, to work with her. "I was truly torn," she said yesterday, "but the reality is that this opportunity is the far bigger challenge."

Evans seemed wistful about the aborted enterprise. "I didn't have enough time at it to mourn it," she said. "We just got our Xerox machine!" She said she hoped to integrate many of her ideas into the established Random House line -- much as she did when she left the Linden Press imprint at Simon and Schuster two years ago to run Simon and Schuster itself.

Kaminsky's departure apparently had not been anticipated in the usually reliable rumor mills of the publishing world.

One prominent literary agent in New York was surprised to hear the news, but had a ready off-the-record explanation. The situation at the top of Random House, he said, "was as if there were two publishers -- and I can tell you their styles were as different as night and day. Bernstein is tweedy, laid-back, from the old school. Kaminsky, who's a cousin of Mel Brooks, is very spontaneous, unpredictable, funny, wacky. I don't think they ever defined the territory."

The availability of Evans to replace Kaminsky on short notice prompted some speculation that she had been positioned to do so all along. Bernstein raised the question of "preplanning" himself, and quickly denied it. Kaminsky referred to "variations on the grassy knoll theory," and dismissed them as quickly. "There is no rancor on my part," he said.

Of his future plans, Kaminsky said, "I'll wash up on some shore in a decent interval. I'm committed to publishing." Evans said, "For the record, I am thrilled."

Staff writer David Streitfeld contributed to this report