WASHINGTON (Reuters) - The U.S. Supreme Court on Friday denied a request by Steve Bannon, an influential ally of former President Donald Trump, to keep him out of prison while he appeals his conviction for contempt of Congress for defying a congressional committee that investigated the Jan. 6, 2021, Capitol attack.

Bannon made the request to the justices on June 21 after a Washington-based federal appeals court rejected his bid to delay him from reporting to prison on July 1 - this coming Monday - as scheduled. Trump is the Republican candidate challenging Democratic President Joe Biden in the Nov. 5 U.S. election. Bannon's sentence could keep him imprisoned for much of the rest of the presidential race.

No justice publicly dissented from Friday's decision.

Bannon was sentenced to four months in prison after being convicted in 2022 of two misdemeanor counts of contempt of Congress. He was charged after he refused to turn over documents or testify to a Democratic-led House of Representatives committee investigating the Capitol riot by Trump supporters who had sought to prevent congressional certification of Biden's 2020 election win.

Bannon was a key adviser to Trump's 2016 presidential campaign, then served as his chief White House strategist during 2017 before a falling out between them that was later patched up. He also has played an instrumental role in right-wing media.

He initially was allowed to delay starting his prison term while he appealed his conviction to the U.S. Court of Appeals for the District of Columbia Circuit. The D.C. Circuit ultimately upheld Bannon's conviction, prompting U.S. District Court Judge Carl Nichols on June 6 to order Bannon to report to prison on July 1.

Bannon would not be the first former top official from Trump's White House to go to prison for refusing to cooperate with the committee. Peter Navarro, a former Trump trade adviser, reported to prison in March after being given a four-month sentence. The Supreme Court declined Navarro's request to remain free during his appeal.

In their filing to the Supreme Court, Bannon's attorneys argued that he should remain free until the justices are able to make a decision on important legal questions in the case. They said that Bannon's conviction should be overturned because he was wrongfully prevented at trial from presenting evidence that he relied upon the advice of his attorney before refusing to provide documents or testify before Congress.

The prosecution during the trial said Bannon showed disdain for the authority of Congress and needed to be held accountable for unlawful defiance. The defense lawyers sought to portray the case as politically motivated.

Trump in 2021 pardoned Bannon on federal criminal charges accusing him of swindling Trump supporters involving an effort to raise private funds to build a wall on the U.S.-Mexico border. Bannon pleaded not guilty to state charges regarding the border wall fundraising and is awaiting trial.

(Reporting by Sarah N. Lynch and Andrew Chung in Washington; Editing by Will Dunham)