By Julia Harte and Mark Hosenball

WASHINGTON (Reuters) - U.S. Attorney General Loretta Lynch did not order FBI Director James Comey to withhold from Congress the discovery of emails potentially related to the investigation into Hillary Clinton's email server, but she made it known that she thought his decision violated department policy, a source familiar with the matter told Reuters on Monday.

As Comey and Lynch aides debated last Thursday whether alerting Congress about the emails would comply with longstanding Justice Department policy against announcing overt investigative steps that would influence an upcoming election, Comey asked whether he was being explicitly directed not to do so.

Lynch never gave Comey the order not to send the emails, a senior government official said.

Comey's letter on Friday notifying members of Congress that the Federal Bureau of Investigation had discovered new emails apparently pertinent to the Clinton server probe has upended the presidential race and given new hope to Republican candidate Donald Trump that he can make a comeback and win on Nov. 8.

Lynch's office informed the FBI on Thursday that sending the letter conflicted with a memo containing official guidance that is sent to all Justice Department employees during presidential election years, according to the official.

The memo instructs employees to "never select the timing of investigative steps... for the purpose of affecting any election."

But the Justice Department made no effort to block the FBI from obtaining a search warrant to review the emails, which the agency received on Sunday. The department is working closely with the FBI on the case.

Assistant Attorney General Peter Kadzik told several members of Congress in letters on Monday that the Justice Department was dedicating "all necessary resources" to work with the FBI on its examination of the newly discovered emails "as expeditiously as possible."

However, an official familiar with the FBI review said investigators could not predict how long the examination would take.

Senator Harry Reid, the Democratic leader in the Senate, sent Comey a letter on Monday accusing the FBI of keeping “explosive information” under wraps about ties between the Trump campaign and Russian officials.

Reid wrote to the FBI in August, requesting information about those ties, including alleged meetings between a Trump adviser and several high-ranking sanctioned individuals in Russia in July, according to a copy of the letter seen by Reuters.

The FBI acknowledged that it received the letter and said it had replied to Reid's office. An aide to Reid said he was not aware of any response from Comey to the letter.

(Reporting by Julia Harte and Mark Hosenball; Additional reporting by Richard Cowan; Editing by Leslie Adler)