Her announcement came hours ahead of Obama's rally in El Dorado, the hometown of his grandfather on his mother's side, and one week before the Kansas caucuses, which are part of the multistate contests Feb. 5. Sebelius said she would attend the event to "welcome him back to Kansas and join the campaign."

Democratic presidential candidates long had sought Sebelius' backing in a state that George W. Bush carried by large margins in the 2000 and 2004 elections. No Democratic nominee for the White House has won Kansas' electoral votes since 1964.

But Sebelius, now in her second term, has shown an ability to triumph in GOP territory. She won re-election in 2006 with nearly 58 percent of the vote. In Kansas, less than 27 percent of the voters are registered Democrats.

For Obama, it was another in a string of high-profile endorsements in the past two days, following on those from Sen. Edward Kennedy, D-Mass.; his son, Rep. Patrick Kennedy, D-R.I.; and Caroline Kennedy, daughter of President Kennedy.

Sebelius has impressed Democrats nationally by election success, and party leaders let her give the Democratic response Monday night to Bush's State of the Union address.