Katherine Harris resigned Thursday as secretary of state, retroactive to July 15. Harris, the state's chief elections official, said she had misunderstood the rules about when she had to quit to run for Congress.

Harris, a Republican who was thrust into the international spotlight during the 2000 presidential election recount, said she intended to quit later this month to focus on the congressional race, saying she can't effectively do both.

But the state's resign-to-run law required her to file a letter stating her intent to resign the day she qualified to run for Congress. If candidates don't do so, state law says they must resign immediately.

"I made a mistake in not filing the letter," Harris said at a hastily called news conference after which she was whisked away by aides as reporters shouted questions.

Harris said it did not occur to her that she was covered by the law because she thought it only applied to offices for which a successor would be elected.

Gov. Jeb Bush will choose her successor. He would have named the next secretary of state anyway -- the position is being eliminated as an elected Cabinet post and turned into an appointed agency head.

Bush spokeswoman Katie Muniz said the governor had accepted the resignation and that Harris would continue in the job as acting secretary of state until he chooses her successor.