By Steve Holland

WASHINGTON (Reuters) - Republican Donald Trump neared the end of his vice presidential search on Thursday and appeared to be leaning toward Indiana Governor Mike Pence, a conservative with the potential to unify divided Republicans.

The presumptive Republican presidential nominee tweeted on Wednesday night that he would announce his choice on Friday at 11 a.m. (1500 GMT) in Manhattan.

The New York businessman is to be formally nominated as the party's candidate for the Nov. 8 election at the Republican National Convention next week in Cleveland. Traditionally, the vice presidential choice is used to build enthusiasm among party loyalists.

Trump's choice of running mate is seen as critical because his defeat of 16 rivals in the Republican primary race left the party divided and some party leaders are still uneasy about some of his campaign positions, and his style.

Sources familiar with campaign operations cautioned that while Pence and former House of Representatives Speaker Newt Gingrich were finalists, Trump could always have a last-minute change of heart and choose someone else from his short list.

A source close to the campaign said Trump appeared to be leaning toward Pence but could easily change his mind.

Gingrich told an ABC News correspondent he expected to hear Trump's decision after 1 p.m. EDT and would not be surprised if Trump chooses Pence.

New Jersey Governor Chris Christie, 53, a former rival to Trump in the presidential race, is also high on the list of potential running mates and provides the kind of counterpunch to Democratic rival Hillary Clinton that Republicans like.

Pence, 57, a former congressman, is seen as a safe choice, not too flashy but popular among conservatives, with Midwestern appeal and the ability to rally more party faithful behind Trump.

Gingrich, 73, is a close adviser to Trump with a wealth of ideas and deep experience in the legislative process from his time as speaker of the House of Representatives in the 1990s.

In what has been an unusually public process, Trump, 70, sat down with both Pence and Gingrich separately in Indianapolis on Wednesday.

He also met with a fourth potential No. 2, U.S. Senator Jeff Sessions, 69, of Alabama, who has been one of Trump's closest advisers.

The New York businessman had dinner with Pence on Tuesday night after they appeared together at a rally. Trump, joined by daughter Ivanka and sons Donald Jr. and Eric Trump, had breakfast with Pence and his wife, Karen, on Wednesday at the governor's residence in Indianapolis.

Trump adviser Ed Brookover told CNN that Trump "first and foremost" wants a running mate who he has good chemistry with and someone who can help him govern best.

(Reporting By Steve Holland; Editing by Peter Cooney and Frances Kerry)