WASHINGTON — In an extraordinary public break with the White House, the FBI warned Wednesday that it has “grave concerns” about a disputed Republican memo on secret surveillance during the 2016 campaign that President Donald Trump has promised to release and that Democrats say is filled with distortions.

The FBI said it only had a “limited opportunity” to review the classified four-page memo prepared by aides to Rep. Devin Nunes, R-Calif., a Trump ally who chairs the House intelligence committee. “As expressed during our initial review, we have grave concerns about material omissions of fact that fundamentally impact the memo’s accuracy,” the nation’s premier law enforcement agency said in a two-paragraph statement.

The intelligence committee’s top Democrat accused the panel’s chairman of making “material changes” to the memo before sending it to the White House to approve its public release, a move he charges should prevent Trump from releasing it.

Ranking Democratic member Adam Schiff, D-Calif., sent a letter late Wednesday to Nunes, accusing him of “deliberately misleading” the committee, demanding he withdraw the version he sent to the White House because “there is no longer a valid basis for the White House to review the altered documents” and approve their public release.

Schiff and Nunes have been bitterly divided over the memo, which the House Intelligence Committee voted along party lines Monday to release to the public, provided Trump does not block their efforts. Schiff charged that the memo was “secretly altered” after that, and that Democrats were only “belatedly” given a chance Wednesday night to see the version sent to the White House, complete with changes that he said members “were never apprised of, never had the opportunity to review, and never approved.”

“It’s clear that Chairman Nunes will seemingly stop at nothing to undermine the rule of law and interfere with the Russia probe,” Senate Minority Leader Charles Schumer, D-N.Y., said in a statement. He accused Nunes of being “willing to carry the White House’s water . . . and now to mislead his House colleagues.”

The public pushback escalates a bitter conflict between the White House and senior officials at the Justice Department, who approved the FBI statement, as well as senior figures in the intelligence community, who have previously warned that release of the classified GOP memo could endanger national security.

The FBI warning, which Nunes dismissed as “spurious objections,” raises the stakes in the Republican effort to discredit the criminal investigation led by special counsel Robert Mueller into whether Trump or his aides collaborated with Russian meddling in the election or obstructed justice.

FBI leaders have clashed with presidents in the past, but usually behind closed doors. Historians struggled Wednesday to find a precedent for the bureau’s public challenge to the White House. “It’s like a neon billboard blinking, ‘Danger, don’t you dare do this,’?” said Douglas Brinkley, a Rice University professor who studies the presidency. “This is a sign of war.”

The FBI decided to go public after FBI Director Christopher Wray and Deputy Attorney General Rod Rosenstein, who is supervising Mueller’s probe, failed to convince the White House or House Republicans that the GOP memo is misleading and its underlying classified material should remain secret.

Wray was allowed to read the classified memo at the House on Sunday, but was not given an opportunity to suggest changes, according to two officials familiar with the process. He asked to make his case in a private briefing with House committee members, but that offer was declined.

The FBI statement was not issued in Wray’s name, but from the bureau itself, an effort to defend an institution that Trump and his allies have said is part of a “deep-state” conspiracy of national security officials to take down the president.

The latest clash is likely to erode Trump’s relationship with Wray. Trump appointed Wray as FBI director after he fired James Comey last May for what the president later said was “this Russia thing.” Comey’s dismissal sparked a national uproar and led to Mueller’s appointment as special counsel.

Despite Wray’s concerns about the memo, the GOP-led House committee voted on a party line on Monday to release it. The committee voted against simultaneously releasing a written rebuttal from Democrats, who claim the GOP memo deliberately misstates facts for partisan purposes.

The decision then moved to the White House, and Trump told a lawmaker after his State of the Union address Tuesday night that he was “100 percent” planning to release the memo. On Wednesday morning, John Kelly, the White House chief of staff, said on Fox News Radio that the memo “will be released here pretty quick, I think, and the whole world can see it.”

The Republican memo reportedly claims that the Justice Department misinformed the Foreign Intelligence Surveillance Court to obtain a secret warrant to conduct surveillance on Carter Page, an adviser in Trump’s campaign who had business ties to Russia, and that it shows the FBI has an anti-Trump bias.

Democrats and law enforcement officials say the four-page GOP memo “cherry-picks” information from a much longer application to the FISA court. Those documents typically run 50 to 60 pages, officials said.

Nunes said Wednesday that he wasn’t surprised that the FBI wants to keep the memo secret. “Having stonewalled Congress’ demands for information for nearly a year, it’s no surprise to see the FBI and [Justice Department] issue spurious objections to allowing the American people to see information related to surveillance abuses at these agencies,” he said in a statement.

joseph.tanfani@latimes.com