He knows, but he’s not saying

One mystery solved: Barack Obama said Thursday that he has decided on his running mate.

And that’s all you’re going to get.

Intent on extending the drama as long as possible, the unofficial Democratic presidential nominee would go no further. Nothing on whether his intended has been notified or the also-rans let down easy. Nothing about when the union might be made official -- although the plan was still that the news would be texted to Obama supporters soon and perhaps unveiled in the flesh at a Saturday extravaganza in Springfield, Ill., where Obama’s campaign began.

Obama and his chief aides have kept a tight lid on the vice presidential selection process, declining to comment even as rumors boomeranged from one potential candidate to another: Would it be Delaware Sen. Joseph R. Biden Jr., Virginia Gov. Tim Kaine, Indiana Sen. Evan Bayh or someone else entirely?

The lid lifted slightly Thursday when Obama confirmed in a USA Today interview that he had come to a decision.

“I won’t comment on anything else until I introduce our running mate to the world,” he told the newspaper. “That’s all you’re going to get out of me.”

Of his options, the Illinois senator said, “We had some great choices.”

He indicated that he was not picking someone who would march in lock step with him: “I want somebody who’s independent, somebody who can push against my preconceived notions and challenge me so we have got a robust debate in the White House.”

Later, asked about the USA Today comments, Obama refused to bite. “I’ve made the selection, and that’s all you’re going to get,” he told reporters at a peanut and gift shop in Emporia, Va.

Presumed Republican nominee John McCain has also been coy about releasing information on his vice presidential selection process, although word surfaced in recent days that he was considering a candidate who favors abortion rights or even a former member of a Democratic ticket -- Connecticut Sen. Joe Lieberman, Al Gore’s vice presidential nominee in 2000, who has since been reelected to the Senate as an independent.

The Arizona senator, who recently has been at his ranch in Sedona, Ariz., made no comment Thursday about his selection process. The announcement is widely expected to be made Aug. 29, after the Democratic convention, which is also McCain’s 72nd birthday.

That timing could serve to lessen Obama’s momentum while escalating GOP enthusiasm leading up to the Republican convention, which begins three days later.

McCain’s campaign has begun encouraging supporters to reserve tickets to an early-morning rally next Friday in Dayton, Ohio.

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stuart.silverstein @latimes.com

maeve.reston@latimes.com

Silverstein reported from Virginia and Reston from Arizona.