By Dustin Volz and Patricia Zengerle

WASHINGTON (Reuters) - Top U.S. intelligence officials will testify in Congress on Thursday on Russia’s alleged cyber attacks during the 2016 election, as President-elect Donald Trump described himself as a “big fan” of intelligence agencies despite casting doubt on their findings that Moscow orchestrated the hacks.

The dishonest media likes saying that I am in Agreement with Julian Assange - wrong. I simply state what he states, it is for the people.... — Donald J. Trump (@realDonaldTrump) January 5, 2017

to make up their own minds as to the truth. The media lies to make it look like I am against "Intelligence" when in fact I am a big fan! — Donald J. Trump (@realDonaldTrump) January 5, 2017

Trump is due to be briefed by intelligence agency chiefs on Friday on hacks that targeted the Democratic Party. President Barack Obama will be briefed on Thursday.

Trump is heading for a conflict over the issue with Democrats and some fellow Republicans in Congress, many of whom are wary of Moscow and distrust the New York businessman’s praise of Russian President Vladimir Putin and efforts to heal the rift between the United States and Russia.

Director of National Intelligence James Clapper, National Security Agency Director Mike Rogers and Undersecretary of Defense for Intelligence Marcel Lettre are due to appear before the Senate Armed Services Committee, which is chaired by Republican John McCain, a vocal critic of Putin.

In the afternoon, State Department and Department of Homeland Security officials will brief the Senate Foreign Relations Committee behind closed doors on the Obama administration’s response to the hacking and harassment of U.S. diplomats.

Their testimony came a week after Obama ordered the expulsion of 35 Russian suspected spies and imposed sanctions on two Russian intelligence agencies over their alleged involvement in hacking U.S. political groups in the 2016 election.

U.S. intelligence agencies say Russia was behind hacks into Democratic Party organizations and operatives before the presidential election, a conclusion supported by several private cybersecurity firms. Moscow denies the hacking allegations.

U.S. intelligence officials have said the Russian cyber attacks were aimed at helping Trump defeat Democrat Hillary Clinton in the Nov. 8 election.

Several Republicans have acknowledged Russian hacking during the election but have not linked it to an effort to help Trump win.

STOLEN DOCUMENTS

Documents stolen from the Democratic National Committee and Clinton campaign manager John Podesta were leaked to the media in advance of the election, embarrassing the Clinton campaign.

In a tweet on Wednesday, Trump said: “(WikiLeaks founder) Julian Assange said ‘a 14 year old could have hacked Podesta’ - why was DNC so careless? Also said the Russians did not give him the info!”

However, on Thursday, Trump said in a post on Twitter that he was not against intelligence or in agreement with Assange.

“The media lies to make it look like I am against ‘Intelligence’ when in fact I am a big fan!” Trump tweeted.

Trump and top advisers believe Democrats are trying to delegitimize his election victory by accusing Russia of helping him.

Some lawmakers, including McCain, said a firmer response was needed to check Russian aggression in cyberspace and elsewhere, and to discourage other countries from trying to influence more U.S. elections.

McCain is among a handful of Republicans to join Democrats in pushing for a special committee to investigate Russia’s political hacking, although that effort faces opposition from Republican leaders in Congress.

Trump has nominated people seen as friendly toward Moscow to senior administration posts, including secretary of state nominee Rex Tillerson, who was awarded Russia’s “Order of Friendship” in 2013 while Tillerson was Exxon Mobil chief executive.

Rogers, the NSA chief, visited Trump in New York in November and is among a handful of people being considered by Trump to succeed the retiring Clapper as U.S. spy chief, in addition to former Republican Senator Dan Coats, according to sources familiar with the matter.

(Additional reporting by Patricia Zengerle and Mark Hosenball in Washington; Editing by Peter Cooney and Bernadette Baum)