President Bush had a surprise for the waiting journalists when he stepped off his chopper at Andrews Air Force Base on Friday morning: It was take-your-daughter-to-work day.

Jenna Bush and her twin, Barbara, started work this week at Bush-Cheney campaign headquarters in Arlington, six weeks after the 22-year-olds celebrated their college graduations. Jenna Bush made her campaign debut by coming along for a day of bus riding across the Philadelphia exurbs and into Amish country.

The day marked a transition for Jenna Bush, a political coming-out for a free spirit who has mostly shunned official publicity. She walked with her father across the tarmac at Andrews after Marine One set down, and they climbed the stairs of Air Force One together. He paused at the top for the customary barrage of waves. She modestly kept walking inside.

Jenna and her sister share an office in Arlington and this week met all the division heads so they would know what everyone does for their dad's campaign. Officials say their duties are undetermined, but both are likely to make occasional public appearances, perhaps emphasizing youth audiences.

Officials said their presence was both a curiosity and a morale boost. One of Vice President Cheney's daughters, Mary Cheney, also works at headquarters as director of vice presidential operations.

Bush's daughters have shown little proclivity for campaigning in the past and have indicated they were not wild about one term, let alone two. But Jenna Bush seemed to enjoy herself Friday. When the bus motorcade stopped briefly in Pottstown, she greeted the emergency medical technicians while her father made quick remarks.

Speaking in the steamy Lapp Electrical Service headquarters in Lancaster, Pa., Bush made eye contact with her as she sat in the front row, and she seemed to signal that he should feel free to wrap it up.

Jenna's dress was chicly casual: shiny brown flared pants ("boot-cut," in Texan); a pink, scoop-neck, wrap-around sweater over a shell that gave the appearance of a bare midriff; heels; and dangling earrings.

At Bush's first event, an "Ask President Bush" rally at a broiling-hot gym in Kutztown, Pa., he began by saying it was a special day for him because of Jenna's company.

"She's already given me good advice," the perspiring president said. "She said, 'Dad, change your shirt.' "

At Bush's final event of the day, in York, Pa., he noted that first lady Laura Bush ("a fantastic, fantastic woman -- I love her dearly") could not be there but had called him on the bus.

"In her stead, traveling with me today is a new graduate from the University of Texas, one of my great daughters, Jenna Bush," he said, to applause. "Made it through in four years, I want you to know."

Jenna Bush accompanied the president for a day of bus rides in Pennsylvania.