By Andrew Goudsward

WASHINGTON (Reuters) -Steve Bannon, who was a senior adviser to former President Donald Trump, faced a skeptical federal appeals court on Thursday as he sought to reverse his criminal conviction for defying a subpoena from a congressional panel that investigated the Jan. 6, 2021, attack on the U.S. Capitol.

Bannon, convicted last year of two misdemeanor counts of contempt of Congress, sought to make the case that he did not receive a fair trial because the judge barred him from making arguments central to his defense, including that his lawyer advised him he did not have to comply with the subpoena.

Bannon "acted in the only way the law permitted him to behave," his attorney David Schoen told a three-judge panel of the U.S. Court of Appeals for the District of Columbia Circuit.

Bannon claimed that he did not have to turn over documents or testify before the Democratic-led House of Representatives special committee because Trump had invoked executive privilege, a legal doctrine that keeps some White House communications confidential.

The court did not appear to be persuaded by Schoen's argument.

Judge Cornelia Pillard noted that Bannon was not working in the White House at the time of the riot and that much of the information the committee sought was unrelated to his interactions with Trump.

"I don't see in the record that there was a response other than 'no,'" Pillard said of Bannon's handling of the subpoena.

Prosecutors at the trial convinced U.S. District Judge Carl Nichols to prohibit that executive privilege defense, arguing that, legally, it did not matter why Bannon refused to cooperate, only that he made a deliberate decision not to comply with the subpoena.

Bannon was sentenced by Nichols in October 2022 to four months in prison and a $6,500 fine. Nichols allowed him to remain free while he appeals.

Outside of the courthouse, Schoen told reporters that if the three-judge panel rejects Bannon's appeal, he would ask the full D.C. Circuit court to review the decision and eventually appeal to the U.S. Supreme Court if necessary.

Bannon, an influential right-wing media provocateur, served as Trump's chief White House strategist during 2017 before a falling out between them that was later patched up. He remains popular on the American right.

The committee sought information from Bannon, citing reports that he had held discussions with members of Congress about blocking the certification of the 2020 presidential election results - Democrat Joe Biden defeated the Republican Trump - and predicted that "all hell is going to break loose" on the day of the Capitol riot.

Trump supporters assaulted police, stormed barricades and swarmed the Capitol in a failed bid to prevent congressional certification of Biden's victory.

Prosecutors said that Trump did not fully invoke executive privilege over Bannon's testimony and that much of the information lawmakers sought from Bannon, who was no longer in the administration at the time of the attack, was not protected.

"Steven Bannon deliberately chose not to comply with a lawful congressional subpoena," Justice Department lawyer Elizabeth Danello said at the hearing.

The House committee disbanded at the end of 2022 without getting information from Bannon.

(Reporting by Andrew Goudsward; Editing by Will Dunham and Scott Malone)