WASHINGTON (Reuters) - The likelihood of a court fight over President Donald Trump's tax returns grew on Wednesday when the U.S. Treasury Department showed no sign of complying with a deadline set by Democratic legislators and Trump himself stuck to his refusal to publicly release them.

Republican Trump has consistently refused requests by politicians, journalists and others, stating his reason for not doing so is that the returns are under audit. Tax and legal experts have said, however, that an audit should not prevent their public release, a practice presidents have followed for decades.

With only hours left before a midnight deadline set for the Treasury Department by the Democratic-controlled U.S. House of Representatives tax committee, the panel said it had not received the returns.

The department, which has consulted with the White House on the panel's demand, did not respond to requests for comment.

Democrats want to review Trump's returns chiefly as part of their investigations into possible conflicts of interest posed by his continued ownership of extensive business interests even as he serves the public as president.

Republicans oppose release of the returns, arguing that it would politicize tax data. The returns of U.S. taxpayers are generally held as confidential by the Internal Revenue Service (IRS), which is part of the Treasury Department.

"There is a high likelihood this ends up in the courts, which is, in a way, unusual because typically when there’s a request like this by Congress, the matter is settled more politically with a compromise," said Jessica Levinson, a professor at Loyola Law School in Los Angeles who specializes in political process law. "But in this case both sides have really dug in."

Legal experts have said that little case law would be available to guide judges if Congress were to take the administration to court over the issue.

Asked about the matter on Wednesday, Trump once again said his tax returns were being audited by the IRS. "I would love to give them, but I'm not going to do it while I'm under audit. It's very simple," Trump told reporters.

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House tax committee Chairman Richard Neal last week requested six years of Trump's personal and business returns from the IRS, invoking a seldom-used law entitling him to make such a request.

Treasury Secretary Steven Mnuchin said in an interview on CNBC television on Wednesday that it was appropriate for his agency to consult with the White House counsel on Neal's request. Mnuchin had said on Tuesday that Treasury Department lawyers had held "informational" discussions with the White House about an expected request for the returns, a step that Democrats criticized as uncalled for under the law.

Democrats say a 1924 statute requires the Treasury secretary to turn over tax returns to the chairmen of the congressional tax committees who ask for them for investigative purposes.

(Reporting by Steve Holland, Jason Lange, Tim Ahmann and Richard Cowan; additional reporting by Susan Heavey; writing by Meredith Mazzilli; editing by Bernadette Baum and Grant McCool)