Bill Clinton (search) came to sell his book on "Late Show with David Letterman" (search) Tuesday night, but left a copy as a gift for Letterman's son.

Reading aloud the inscription in his hefty 957-page memoir, the former president wished Harry Letterman (born to Dave and his girlfriend, Regina Lasko, Nov. 3) a happy 9-month birthday.

"With luck," Clinton went on, "you will finish this by your 21st birthday. Meanwhile, carry it around and build more muscles than your dad has."

Looking natty in a blue suit and pink tie, Clinton shared the bill with only musical guest Natalie Merchant (search). During his extended interview, he quickly moved from promoting "My Life" (search) (which since its June 22 release has sold more than 1.5 million copies) to politics and global affairs.

Still, he managed to do a little more selling, putting in a few good words for Sen. John Kerry (search), the newly anointed Democratic presidential candidate.

"Of all the people I dealt with in Congress," Clinton said in part, "he cared the most about trying to find programs that would keep young, inner-city minority kids out of trouble and out of jail and in school.

"There were no votes in this for John Kerry ... He just did it cause he thought it was right."

When asked whether the economy or the war in Iraq would be the deciding issue in the presidential election, Clinton replied, "I think the security question is a threshold question.

"I believe if the voters can get it fixed in their mind that they can trust Sen. Kerry to fight the war against terror and keep us safe at home, that it's more likely than not he will win, because after 9-11 the Bush administration went way to the right on domestic policy."

Mostly serious while interviewing Clinton, Letterman posed a mischievous question as their session neared an end.

"Tell me what you know about Sandy Berger sticking documents in his pants and walking out of the National Archives," Letterman asked.

Clinton chuckled, then praised his former national security adviser, who is facing allegations of mishandling highly classified terrorism documents.

"Anybody that ever saw Sandy Berger's office at the White House would not be surprised that he gets the papers mixed up or takes the wrong ones away," Clinton grinned. "He's got a well-organized mind and a disorganized desk."

Clinton last appeared on Letterman's CBS late-night show on Sept. 11, 2002, the first anniversary of the 2001 terrorist attacks. He is now mulling an offer from NBC's "Saturday Night Live" to be a guest host in the coming season, according to anonymous sources quoted by TV Guide Online. A decision is expected this week.