PENSACOLA, Fla. — Sen. John McCain disclosed Wednesday he is in the "embryonic stages" of selecting a vice presidential running mate and hopes to unveil his choice before the Republican National Convention to avoid the type of problems that plagued Dan Quayle's debut two decades ago.

"It's every name imaginable" he said of his list-in-the-making, about 20 in all.

He disclosed none of them and declined even to identify the individuals he has approached to supervise the vetting that will inevitably winnow the field.

In expressing his hope to announce his choice before the convention opens in September, McCain added, "I'm aware of enhanced importance of this issue because of my age." He is 71, and if he wins, would be the oldest president elected.

McCain's comments seemed to startle his top aides, who have scripted an elaborate weeklong series of events designed to introduce the Republican to a wider audience of voters and emphasize his military service.

The day's itinerary included stops at the Naval Academy in Annapolis, Md., where McCain graduated in 1958, and Pensacola, Fla., where he took his flight training.

There, he drew a loud ovation when he said, "We could and should call on universities to allow ROTC a presence on their campuses. That they are frequently denied that privilege is disgraceful."

The Arizona senator's remarks on a vice presidential search made clear his campaign has entered a new phase after a month spent asserting control over the party apparatus, emphasizing fundraising and trying to heal the wounds of a hard-fought struggle for the GOP nomination.

"We've done a pretty good job of unifying our party," he told reporters as his campaign bus pulled away from the football stadium at the Naval Academy, where he had issued a call for citizen involvement. "Now we've got to energize our party."

Aides interjected at one point that polling data shows McCain's level of support among Republicans is on par with the backing President Bush had at the same point in his winning campaigns in 2000 and 2004.

McCain indicated that little or no significant vetting of potential running mates has occurred. "I've just started this process of getting together a list of names and having them looked at," he said, adding it could take months to complete.

Early speculation on a running mate has focused on his former rivals for the nomination, particularly former Arkansas Gov. Mike Huckabee, as well as a handful of sitting Republican governors, Charlie Crist of Florida and Tim Pawlenty of Minnesota among them.