CORRECTED: John McCain has big decision: Who to pick as VP

(Corrects Powell’s title in 12th paragraph to former Chairman of the Joint Chiefs of Staff from Secretary of Defense) By Steve Holland

WASHINGTON (Reuters) - Republican presidential candidate John McCain has a big decision ahead of him -- picking a vice presidential running mate whose presence on the ticket would reassure Americans concerned about McCain's age.

McCain is 71 years old and would be the oldest person ever elected to a first presidential term. He has survived a bout with melanoma that left a long scar on his face and suffered harsh treatment as a Vietnam prisoner of war.

Voters do not typically base their vote on the vice presidential choice but they do want to be assured that the running mate would be able to take over if the president were to die or become incapacitated.

When questions arose about Ronald Reagan's age (69) during the 1980 election, Reagan picked one of the men he had vanquished for the Republican presidential nomination, George H.W. Bush, and Bush's reassuring presence largely silenced questions about Reagan.

It is a scenario not lost on the McCain team, which is waiting to seal the Republican presidential nomination before launching a search for the No. 2.

"For Reagan in 1980, age was a big question, was a bigger issue than it is for McCain," said McCain adviser Charlie Black. "The day Reagan picked George Bush, it went away. People looked at it and said, 'Oh, we know this guy, we know he can handle it.'"

By contrast, Americans were so disenchanted with Bush's vice president, Dan Quayle, that the Bush team considered but decided against dumping Quayle from the ticket in the elder Bush's 1992 re-election bid, which he lost.

Douglas Brinkley, a presidential historian, said McCain has a compelling history as a former Navy fighter pilot and long-time Arizona senator.

"But at 71 years old and afflicted with cancer and a life that has brutalized his body in many ways, I think who he picks is going to be very, very important," Brinkley said. "You're really looking at somebody who over an eight-year period could be president."

NOT NECESSARILY A BALANCING ACT

It does not necessarily mean McCain must pick someone far younger.

"I don't think you're going to balance the ticket on age," said Republican strategist Scott Reed. "Pick someone who is going to help you win and who can step in and serve as president if there is a crisis."

Brinkley said the most reassuring person McCain could pick in the Republican Party would be retired Gen. Colin Powell, a former secretary of state and former Chairman of the Joint Chiefs of Staff.

Powell, 70, has said he does not want the job but Brinkley said Republican Party elders might be able to persuade him.

"Powell is someone everyone could imagine as president," Brinkley said.

Two possibilities include Florida Gov. Charlie Crist, 51, who could help McCain win the battleground state of Florida in the November election, and Minnesota Gov. Tim Pawlenty, 47, who could do the same in Minnesota.

There are plenty of other names: Texas Sen. Kay Bailey Hutchison, who says she does not want it; South Carolina Sen. Lindsey Graham; Mississippi Gov. Haley Barbour; Texas Gov. Rick Perry; and former White House budget director Rob Portman, a former member of the U.S. Congress from Ohio.

Republican pollster Whit Ayres said McCain's choice may well depend on whether Democrat Barack Obama or Hillary Clinton wins the nomination.

"A vice presidential nominee against one might not be the best choice if you're running against the other," Ayres said. "If it's Clinton, it might place a higher premium on a woman. If it's Obama, it might place a higher premium on an African-American."

(Editing by Doina Chiacu)

(To read more about the U.S. political campaign, visit Reuters "Tales from the Trail: 2008" online at blogs.reuters.com/trail08/)