By Steve Holland

WASHINGTON (Reuters) - Republican Donald Trump conducted last-minute talks with his top potential picks for his vice presidential running mate on Wednesday, trying to choose among three experienced politicians, each with unique strengths and weaknesses.

In Indianapolis, Trump had a breakfast meeting with Indiana Governor Mike Pence, and later sat down for talks with former U.S. House of Representatives Speaker Newt Gingrich. His family met on Tuesday with New Jersey Governor Chris Christie, who speaks to Trump on a near-daily basis.

In addition, U.S. Senator Jeff Sessions, 69, of Alabama, a fourth potential candidate for the No. 2 spot who has been a close adviser to Trump, was seen going into the Conrad Hotel in Indianapolis, where Trump was.

A source close to the campaign said Trump appeared to be leaning toward Pence but that he could always change his mind. "It's not done until it's done," the source said.

Trump seemed to be trying to decide between Pence and Gingrich, the source added.

Trump will make the announcement on Friday in New York, CNN reported, citing campaign chairman Paul Manafort.

The New York businessman is to be formally nominated at the Republican National Convention next week in Cleveland. Traditionally, the vice presidential choice is used to build enthusiasm among party loyalists.

Pence, who faces a Friday deadline on whether to have his name on the ballot to seek another term as governor, said he was humbled to be considered for Trump's running mate.

"I think he's giving it very careful consideration, and we’re humbled to be a part of that," Pence told reporters later. "There are a number of other noteworthy Americans that they are considering, and I'm just honored to be on that list."

Republicans close to the campaign said they believed Trump had narrowed his short list to Pence, Gingrich and Christie.

He has campaigned with all three in recent days as he girds for perhaps the most consequential decision of his campaign ahead of the Nov. 8 election.

In a sign of how seriously the campaign is considering Pence, Trump was joined at the governor's residence for breakfast by his daughter Ivanka, son-in-law Jared Kushner and sons Donald Trump Jr. and Eric Trump. Kushner and Trump's children have played important roles in the campaign.

Trump's children met with Christie on Tuesday, a source close to the governor confirmed, describing the meeting as good and saying both parties had an existing relationship and were already friendly.

Trump, who wants an experienced politician to join him on the ticket, campaigned with Pence at a rally on Tuesday night in Westfield, Indiana.

'MORE ATTENTION THAN USUAL'

The presumptive Republican nominee has a tough choice to make.

Pence, a 57-year-old former congressman who has flirted in the past with a presidential run of his own, would be perhaps the safest choice for Trump given the governor's popularity among conservatives and his experience in government. He would also bring Midwestern appeal.

But Pence has had a couple of missteps as Indiana's chief executive. A religious freedom law he signed had to be revised because it was seen as discriminating against gays and lesbians, and he had to abandon plans to create a state-run news agency.

"Throughout history vice presidential selections seldom make much difference in the election. Because Trump has never held office and people are anxious to see how he would assemble a government, this pick might get more attention than usual," said Republican strategist Charlie Black.

"Pence would be a very good pick from the standpoint of having federal and state government experience, and also he has been a card-carrying member of the conservative movement his whole life," Black said.

Trump is clearly comfortable with both Gingrich and Christie, a factor that Trump advisers say is important to him. Both Gingrich and Christie have been supportive of Trump throughout much of his bitter feud with establishment Republicans.

Gingrich is popular among many Trump advisers because of his grasp of policy and his counsel. He was House speaker when Democrat Bill Clinton was president in the 1990s, and they achieved welfare reform, among other legislative achievements.

"Trump has staked his candidacy on revolutionary change in Washington and there is no one being considered who has actually achieved revolutionary change like Newt Gingrich," said Rick Tyler, a former spokesman for Gingrich. "If Trump picks him, I’ll know that Trump is serious about reforming Washington."

But at age 73, Gingrich could have trouble appealing to younger voters. Trump is 70.

Christie, 53, a one-time rival to Trump in the presidential race, is seen as a kindred spirit of Trump who would be a strong counterpuncher to Democrat Hillary Clinton, 68. But many conservatives doubt he really is one of them.

(Additional reporting by Mohammad Zargham, Ginger Gibson and Eric Beech in Washington; Editing by Jonathan Oatis and Peter Cooney)