By Phil Stewart and Idrees Ali
WASHINGTON (Reuters) - President-elect Donald Trump's pick to lead the Pentagon told Congress on Thursday the United States must be ready to confront Russian behavior in areas where the two countries cannot cooperate, even as he backed Trump's bid to engage with Moscow.
The remarks by retired Marine General James Mattis in written responses to questions from Congress appeared set to endear him to Russia-wary Republicans and Democrats on the Senate Armed Services Committee, which is expected to back his nomination.
"We engaged with Russia even during the darkest days of the Cold War, and I support the President-elect’s desire to engage with Russia now," Mattis wrote.
"At the same time, when we identify other areas where we cannot cooperate, we must confront Russia’s behavior, and defend ourselves if Russia chooses to act contrary to our interests."
Due to enter the White House in eight days, Trump on Wednesday acknowledged that Russia likely hacked the Democratic National Committee and emails of top Democrats during the 2016 presidential election campaign, a conclusion reached by U.S. spy agencies.
Mattis cited Russian involvement in hacking and information warfare among the challenges posed by Moscow. Others include treaty violations, using tactics short of open war to destabilize other countries and "alarming messages from Moscow regarding the use of nuclear weapons," he wrote.
Senator John McCain, the Republican chairman of the committee, said he "could not be happier" about Mattis' nomination. He warned sternly against optimism about engaging with Russian President Vladimir Putin.
"Putin wants to be our enemy. He needs us as his enemy. He will never be our partner," McCain exclaimed in his opening remarks.
"He believes that strengthening Russia means weakening America. We must proceed realistically on this basis."
Mattis, who retired from the military in 2013, is technically ineligible for the job since he has not been a civilian for at least seven years. That means Congress would need to grant him a waiver, something it has not done since 1950, but appears inclined to do now.
In his opening statement, Mattis said he can lead the military as a civilian, even after a 44-year military career.
"I recognize my potential civilian role differs in essence and in substance from my former role in uniform," Mattis said..
Mark Cancian, a senior adviser at the Center for Strategic and International Studies, said he expected bipartisan support for Mattis would help him overcome that hurdle.
"The other thing he has going for him is that he may be a restraint on some of Trump's more extreme impulses," Cancian said. "The concern that people would have is OK, you vote down Mattis, who do you get?"
Senators are expected to ask Mattis how he would grapple with Iran's influence in Iraq, Syria, Yemen and beyond.
Officials who knew him before he retired in 2013 said Mattis clashed with top Obama administration officials when he headed the military's Central Command over his desire to better prepare for potential threats from Tehran.
"Iranian malign influence in the region is growing. Iran is the biggest destabilizing force in the Middle East and its policies are contrary to our interests," Mattis said in his written responses.
On Iraq, Mattis said the main goal should be to ensure "that it does not become a rump state of the regime in Tehran."
Mattis, 66, has tried to persuade Trump privately against the use of waterboarding, which simulates drowning, as an interrogation tactic. Top U.S. officials, many lawmakers and human rights groups have denounced waterboarding as torture.
Mattis also voiced support for strong international alliances in his remarks and said the NATO alliance was central to America's defense.
"History is clear: nations with strong allies thrive and those without them wither," he said.
(Additional reporting by Steve Holland, Jonathan Landay and Patricia Zengerle; Editing by Howard Goller and Alistair Bell)