* Tradition is to name running-mate right before convention
* Some see advantage in going early
* Potential vice president list closely guarded secret
By Steve Holland
WASHINGTON, June 1 (Reuters) - Senator John McCain waited until just before the 2008 Republican convention to name his vice presidential pick, sticking to a timing tradition thought to pump up party activists before the big push to Election Day.
This year, there is at least a small chance that Republican Mitt Romney might break with tradition and name his vice presidential choice earlier in the summer, according to people advising the campaign.
Romney and a small circle of confidants are working quietly on a list of high-profile Republicans being considered for the No. 2 position. The confidants include his wife, Ann, long-time adviser Beth Myers and campaign manager Matt Rhoades.
Outside advisers to the Romney campaign, who spoke on condition of anonymity, say he has the option of announcing his choice well before the Republican convention where Romney will be nominated, in Tampa in late August.
The tradition is to announce the No. 2 around the time of the convention to inspire grassroots activists and seek maximum publicity for the final two-month push to the Nov. 6 election.
But in this case, the Romney team has discussed whether to announce the pick a few weeks earlier to generate buzz for his campaign during August and help raise campaign funds.
It is far from clear, according to the outside advisers, on whether this route will be taken. But many Republicans see an advantage in going early.
"You double your ability to campaign, you double your ability to raise money," said one Republican official. "You get a longer media halo," said another.
Romney's list is a closely guarded secret, but speculation has centered on a host of Republican leaders including Ohio Senator Rob Portman, Florida Senator Marco Rubio and New Jersey Governor Chris Christie.
Over the coming weeks, those on the list will undergo a background investigation, turning over financial records and any other documents to lawyers hired by the campaign to provide as full a picture as possible of their lives.
THE VETTING WINDOW
Chris Lehane, a Democratic strategist who was a senior adviser to Al Gore's 2000 presidential campaign, said the probing is extensive because the vice presidential choice is the first high-profile decision the candidate makes and it must be done correctly to show Americans the candidate can be trusted.
"It was everything you could imagine, making available your tax returns over X number of years, documents on everything you owned, anything that could prove embarrassing," said Lehane.
Gore started out with about 20 names. Then the list was cut to 10 and then down to five and the rigor of the vetting became more serious. He eventually chose Senator Joe Lieberman, a moderate Democrat who later became an independent and was a top choice for McCain in 2008.
"A lot of these folks didn't get through the initial vet - not necessarily because of anything scandalous. You start to look at votes, at positions. At the end of the day you end up with a limited number of folks," said Lehane.
Once the vetting is complete, only a handful of names are usually left, leaving the candidate with a choice of which direction to go in.
"At that point it's a decision for the candidate for his comfort level, confidence in the person and maybe political considerations," said a Republican official involved in past vetting procedures.
Romney could try to appeal to Hispanics, for example, by picking the Cuban-American Rubio, or he could try to improve his chances in the swing state of Ohio by choosing Portman. Many other names offer similar scenarios.
Romney's campaign says his main qualifications are for someone who could take over as president should anything happen to him, and someone with whom he has a high level of comfort.
Most Republican analysts expect him to pick a relatively safe choice to avoid a repeat of McCain's 2008 pick of former Alaska Governor Sarah Palin, who enlivened the Republican conservative base but was seen as not up to the job of vice president.
(For complete coverage of the U.S. presidential campaign please click on ) (Editing by Mary Milliken and Vicki Allen)