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ST. PAUL, Minn. -- The McCain campaign scrambled to take control of the public debate over vice-presidential pick Sarah Palin, canceling her public appearances and teaming her with high-powered Republican operatives as she prepared for a speech Wednesday night that will be her first, and perhaps most important, chance to define herself to the American public.

Campaign officials were heartened by the strong support the Alaska governor continued to receive in the halls of their nominating convention here, a day after the revelation that her 17-year-old unmarried daughter, Bristol, was pregnant.

Gov. Palin and her husband "have embraced the grandchild about to be born," Gary Bauer, a social conservative activist and onetime presidential candidate, told the Texas delegation. "They already are teaching America a lesson about the sanctity of life," he added, as the delegates jumped to their feet in applause.

But Republican officials remained nervous about how the choice was playing in the country as a whole. Some new polls showed Democratic nominee Sen. Barack Obama gaining a big lead in recent days following his party's convention last week.