He blamed Democrats for news reports on the intelligence findings and said he did not believe they came from the Central Intelligence Agency.
"I think it's ridiculous. I think it's just another excuse. I don't believe it," Trump said in an interview on "Fox News Sunday."
Trump's reluctance to blame Russia for interfering in the U.S. election has raised concerns among U.S. officials who fear he will go soft on Moscow at a time when they are worried about its increasingly aggressive behavior on cyber attacks and in Crimea, Ukraine and Syria.
A U.S. intelligence official, speaking on condition of anonymity, harshly criticized Trump's rejection of the assessment that Russian hacking was intended to boost the president-elect's prospects in the Nov. 8 election.
"It's concerning that intelligence on Russian actions related to the U.S. election is being dismissed out of hand as false or politically partisan," said the U.S. intelligence official.
"The inclination to ignore such intelligence and impugn the integrity of U.S. intelligence officials is contrary to all that is sacred to national security professionals who work day and night to protect this country."
The unusually harsh comment underscored the unprecedented tensions that Trump has created with the intelligence community he will command even before he's been sworn into office.
Two leading U.S. Senate foreign policy voices from Trump's own party expressed alarm on Sunday about the possibility of Moscow tipping the scales in favor of an American presidential candidate and promised to begin investigating immediately.
The Obama White House, which has ordered intelligence agencies to review cyber attacks and foreign intervention in the 2016 election, has formally accused Russia of a campaign of cyber attacks against Democratic Party organizations ahead of the presidential election.
Russian officials, who have previously vehemently denied accusations of interference in the U.S. election, were quiet.
In his search for a secretary of state, Trump, a New York real estate magnate, is strongly considering Exxon Mobil Corp Chief Executive Rex Tillerson, who has close ties with Moscow and has spoken out against U.S. sanctions on Russia.
Republican Senator John McCain expressed concern about Tillerson's close relationship with Russian leader Vladimir Putin. "That would color his approach to Vladimir Putin and the Russian threat," he said on Sunday on CBS' "Face the Nation."
A number of U.S. senators have expressed concerns about Tillerson, suggesting his nomination could run into trouble in the Senate.
Trump's pick as national security adviser, retired Army Lieutenant General Michael Flynn, has also raised eyebrows in military circles through appearances on Russia's government-run broadcaster RT, particularly at a gala last year attended by Putin.
But Trump's choices to lead the CIA and the Pentagon, U.S. Representative Mike Pompeo and retired Marine General James Mattis, are more likely to take a harsher stance on Russia.
U.S. intelligence agencies have told Congress and President Barack Obama's administration that Russia has grown increasingly aggressive in Syria and Ukraine and has stepped up activities in cyberspace, including meddling, sometimes covertly, in European and U.S. elections.
A senior U.S. intelligence official told Reuters that intelligence agencies had concluded with "high confidence" that not only did their Russian counterparts direct the hacking of Democratic Party organizations and leaders, but did so to undermine Democratic candidate Hillary Clinton.
CONGRESS TO INVESTIGATE
Trump questioned whether the CIA was behind the reports that indicated Moscow wanted him in the White House. "I think the Democrats are putting it out," he said in the Fox News interview.
He said the intelligence community did not agree on Russian intervention. "They're fighting among themselves. They're not sure," he said.
McCain was at a loss on Sunday to explain Trump's repudiation of the Russian meddling.
"I don't know what to make of it because it's clear the Russians interfered," McCain said on CBS.
"Whether they intended to interfere to the degree that they were trying to elect a certain candidate, I think that’s a subject of investigation, but the facts are stubborn things."
McCain and fellow Republican Senator Lindsey Graham joined Democratic Senators Chuck Schumer and Jack Reed on Sunday in expressing concern over possible Russian interference and said they would work together to investigate such cyber attacks.
"Recent reports of Russian interference in our election should alarm every American," they said in a statement. "This cannot become a partisan issue. The stakes are too high for our country."
McCain, chairman of the Armed Services Committee, said he would have a subcommittee led by Graham begin investigating the Russian hacking immediately.
Republican House of Representatives Speaker Paul Ryan cannot comment on classified briefings, "but he rejects any politicization of intelligence matters," spokeswoman AshLee Strong said in an email.
Trump advisers disputed elements of the news reports, focusing particularly on a New York Times story saying that intelligence officials concluded the computer systems of the Republican National Committee also had been hacked. The fact that material from that intrusion had not been released, the Times reported, supported the conclusion that Russia was trying to help Trump.
"The RNC was absolutely not hacked,” the RNC chairman and incoming White House chief of staff, Reince Priebus, said on NBC's "Meet the Press."
Trump adviser Kellyanne Conway said Trump would not interfere with any congressional inquiry but that the president-elect regarded the spate of hacking reports as part of an effort to relitigate the election.
"He absolutely respects the intelligence community," Conway said on CBS. "What he has said is laughable or ridiculous is that this was meant to elevate him to the presidency."
In the "Fox News Sunday" interview, Trump also discussed his decision to receive the President's Daily Brief, or PDB, a highly classified document that can include details of U.S. and allied covert operations, once a week, far less often than most of his predecessors.
Trump said a number of his top advisers received the briefing and he did not need to get the report more frequently under routine circumstances. "I don't need to be told the same thing every day, every morning - same words. 'Sir, nothing has changed. Let's go over it again.' I don't need that," he said.