WASHINGTON (Reuters) - The U.S sees it as a "very open question" whether Venezuelan President Nicolas Maduro can win re-election if he holds a free vote in July, and Washington is trying to ensure the ballot is credible in the face of significant obstacles, a senior U.S. official said on Friday.

The Biden administration is engaging with Venezuelan "stakeholders" as well regional and European partners in a bid to keep the electoral process on track but expects additional difficulties as the July 28 vote approaches, the official said on conditional of anonymity.

Maduro is vying against Edmundo Gonzalez, veteran ex-diplomat who was named main opposition candidate after primary winner Maria Corina Machado had a ban on holding office upheld by the Supreme Court, a move condemned by the U.S. at the time. Machado has since given Gonzalez her backing.

The U.S reimposed oil sanctions on OPEC-member Venezuela last month, accusing Maduro of not fully complying with deals reached with the opposition to ensure free and fair elections.

Still, Washington says Maduro has met some of his commitments, including setting an election date and allowing an opposition candidate to run. "We are closely monitoring whether there is any backtracking," the senior administration official told reporters.

With a recent poll showing any candidate backed by Machado having more than double Maduro's support, opposition members have warned the ruling Socialist party could take action to bar Gonzalez from appearing on the ballot.

Maduro, whose 2018 re-election was rejected by Western governments as a sham, has presided over a sharp economic decline.

"The prospect for a free and fair election or even a minimally credible election remains one that we are very interested in seeking to advance, but we recognize also there are significant obstacles," the official said.

"Whether or not Maduro could win an election in Venezuela is at best a very open question. Certainly there is a significant amount of polling that that is not the case."

The Venezuelan government did not immediately respond to a request for comment.

Asked whether there could be a change in U.S. policy toward Venezuela after July 28, the official said the response would depend heavily on how the election is conducted.

The U.S. Treasury Department said it would consider specific licenses on a case-by-case basis for companies to operate in Venezuela after it withdrew a broad license last month that had eased sanctions.

The prospects for individual licenses is seen by experts as a way for the U.S. to temper any impact on global oil supplies, and the official said it also may have a "moderating impact" on how Maduro's government acts ahead of the election.

The official also reiterated the U.S. call for Venezuela to grant safe passage out of the country for a group of opposition activists sheltering at the Argentine embassy in Caracas.

(Reporting By Matt Spetalnick and Steve Holland; writing by Matt Spetalnick; Editing by Cynthia Osterman)

By Matt Spetalnick and Steve Holland