“I have to warn you, I’m not just some sitcom guy. I’m now an author,” said Bob Newhart, before he broke into a laugh. And if you need a laugh — and who doesn’t these days — get a copy of his no-holds-barred book, “I Shouldn’t Even Be Doing This” (Hyperion). Luckily, this isn’t the final chapter of his full career. At 77, he says “I have no intention of retiring; I can’t imagine not doing stand-up. That’s where I started and where I’ll be.” He performs about 30 stand-up dates a year and he’d probably do more but admits, “Now, the travel is the hard part.” His “live” comedic performances are only a part of his repertoire. The serious actor Bob Newhart was in three “E.R.” segs last year and this past August, in South Africa, he starred in a sequel to TNT’s “The Librarian 2: Return to King Solomon’s Mines,” after which he and wife Ginny went on safari. Among his long list of accomplishments include 87 guest hosts on “The Tonight Show” and a six-year sitcom experience with Suzanne Pleshette, whom he’s cheered up on the phone as she undergoes chemotherapy. He eschews political jokes in his performances “because they cost you half of your audience. And the jokes are on the air on the late show that night.” However, he writes that he campaigned for JFK “Because everyone knew that unless you helped elect the first Catholic president, you would go to hell,” he laughed. The book, of course illustrates the Newhart- Don Rickles relationship. “Don Rickles and I are best friends. I know that might seem strange to those who know Don only by reputation, but somebody has to be his friend. Just to make sure I don’t forget, Don gave me a doormat that sits just outside the front door of my house. It reads: ‘The Newharts: The Rickleses Best Friends.” Newhart seriously says his most prized moment was being inducted into the TV Hall of Fame. He’s now looking forward to his life’s new chapter: the book tour. “It’s a new experience,” he said enthusiastically.