SPRINGFIELD, Ill. — Barack Obama's newly minted running mate will join the Democratic hopeful onstage Saturday at a rally in this capital city where Obama launched his White House bid, a campaign official said.

A senior Obama adviser told The Associated Press on condition of anonymity Tuesday that Obama and his vice-presidential choice will appear in front of the former state Capitol where Abraham Lincoln once served. The last time Obama appeared there, he announced he was running for president.

The disclosure narrowed the window Obama has to reveal his running mate. The list of possibilities is widely believed to be down to Delaware Sen. Joe Biden, Kansas Gov. Kathleen Sebelius, Indiana Sen. Evan Bayh and Virginia Gov. Tim Kaine, who planned to campaign with Obama Thursday in his home state.

Obama strategist Anita Dunn wouldn't respond directly when asked if the Springfield event would be Obama's first appearance with his choice, but she suggested the two wouldn't necessarily be related. The campaign has said it will announce the choice in a cell phone text message to supporters.

"We could pick up the v.p. any time," Dunn said in an interview.

The campaign's announcement said only that the Illinois senator would begin his trip to the party's national convention at Saturday's event. The Democratic National Convention begins Monday in Denver.

At a town-hall meeting in Raleigh, N.C., Obama repeatedly said "he" when discussing the qualities he sought in a potential running mate, even as campaign officials cautioned not to read much into his choice of pronouns.

"Let me tell you first what I won't do: I won't hand over my energy policy to my vice president and not know necessarily what he's doing," Obama told the audience. "My vice president ... will be a member of the executive branch. He won't be one of these fourth branches of government where he thinks he's above the law," an apparent reference to Vice President Dick Cheney's handling of his office.

Those believed to be on Obama's short list stayed mum.

Biden coyly told reporters staking out his home in Delaware, "I'm not the guy," as he drove by. Sebelius, in an interview with the AP before she stumped for Obama in Michigan, professed no inside knowledge of when word would come.

"A week from tomorrow we will all know," she said, referring to when the running mate is scheduled to accept the nomination at the convention.