WASHINGTON, January 12 (Reuters) - President-elect Donald Trump's pick to lead the Pentagon is expected to field tough questions about civilian control of the military as well as future U.S. policy toward Russia and Iran during his Senate confirmation hearing on Thursday. James Mattis, who retired as a four-star Marine general 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 will make the case that 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 will testify, according to prepared remarks. Mattis, 66, is believed to advocate a stronger line against Moscow than the one Trump outlined during his election campaign and has argued persuasively in private talks with Trump against the use of waterboarding, which simulates drowning, as an interrogation tactic. Those attributes, as well as his past remarks extolling the NATO alliance, which Trump also criticized in the campaign, are expected to help sway many Democrats and Republicans skeptical of some of Trump's campaign positions. Mattis made clear his support for strong international alliances in remarks to the Senate Armed Services Committee. "History is clear: nations with strong allies thrive and those without them wither," Mattis will testify at the hearing, due to begin at 9:30 a.m. (1430 GMT). Mark Cancian, a senior adviser at the Center for Strategic and International Studies, said he expected Mattis would not have a difficult time securing the nomination, partly because he enjoys bipartisan support. "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 Central Command over his desire to better prepare for potential threats from Tehran. His support for stiffer responses to Russia could endear him to Republicans. Senior Republicans on the committee are pushing for a harsher response to what U.S. spy agencies say was the Kremlin's meddling in the U.S. presidential election. [nL1N1EZ1LJ] Trump, who takes office on Jan. 20, has expressed a desire to improve ties with Moscow. WATERBOARDING, EAVESDROPPING Mattis' confirmation hearing comes the same day that U.S. Representative Mike Pompeo, Trump's choice to be the next CIA director, goes before the Senate Intelligence Committee. Lawmakers are expected to ask about his support for the U.S. government's now-defunct sweeping collection of Americans' communications data and for the CIA's use of harsh interrogation techniques on detainees in secret overseas prisons during the Bush administration. In a Wall Street Journal op-ed published in January 2016, the conservative lawmaker from Kansas called for a resumption by the National Security Agency of the bulk collection of domestic telephone metadata, which comprises numbers called, the times of calls and the locations from where and to where they are made, but not the actual conversations. Pompeo has argued that the CIA's program of so-called Enhanced Interrogation Techniques, which included waterboarding, produced useful intelligence. A 2014 Senate Intelligence Committee report concluded that the techniques, decried as torture by many lawmakers and human rights experts, produced no significant intelligence. In excerpts of his opening statement released in advance, Pompeo pledged to shed the political role he had played as a three-term member of the House of Representatives and "stay clearly on the side of collecting intelligence and providing objective analysis to policymakers." "This is the most complicated threat environment the United States has faced in recent history," said Pompeo, who served as an Army officer in Europe during the Cold War. He pledged that under his leadership, the CIA would "aggressively pursue collection operations and ensure analysts have the time, political space, and resources to make objective and sound judgments."