Running as a Republican in a heavily Democratic district in Texas against a five-term incumbent, Ms. Klein, 39, has received more in donations and fund-raising help from the telecommunications and power industries than any other rookie candidate in the nation.

Because administration officials have said that in the event of a second Bush administration she would be considered by the president, whom she served as a senior policy adviser when he was governor of Texas, as a candidate to be the next head of the Federal Communications Commission.

"The reason they've told me that they support me is that they appreciated that I had integrity," Ms. Klein said. "Even though we disagreed, it was harmonious."