WASHINGTON — Rex W. Tillerson on Wednesday told a Senate committee weighing his nomination as secretary of state that he would push back hard against President Vladimir V. Putin’s effort to expand Russian influence from Ukraine to Syria to cyberspace. But in a rocky all-day hearing, Mr. Tillerson also found himself on the defensive when it came to Exxon Mobil’s lobbying activities and his reluctance to declare that some dictators were violators of human rights.
One especially skeptical Republican was Senator Marco Rubio of Florida, whose vote on the Foreign Relations Committee might well decide the fate of Mr. Tillerson, the former chief executive of Exxon.
In one contentious exchange with Mr. Rubio, who ran against President-elect Donald J. Trump last year for the Republican nomination, Mr. Tillerson rebuffed an effort to get him to describe Mr. Putin as a war criminal for ordering the bombing of civilians in Chechnya. “I would not use that term,” he said.
By the end of the day, Mr. Rubio would not commit to supporting Mr. Tillerson, saying he was “prepared to do what’s right,” even if it meant siding with Democrats, which would most likely result in a 11-to-10 committee vote against the nomination. Even so, the committee could still send it to the full Senate, where Mr. Tillerson’s chances would be tenuous.
On issue after issue — the dangers of letting Japan and South Korea obtain nuclear weapons, his opposition to a ban on Muslim immigration, the need to push back hard against Mr. Putin’s efforts to expand Russian influence — Mr. Tillerson showed considerable independence from Mr. Trump, separating himself from many of the president-elect’s campaign pronouncements. While Mr. Trump described an America that would defend allies only if they paid their fair share, Mr. Tillerson repeatedly emphasized fulfilling alliance commitments.
Mr. Tillerson came to the hearing acutely aware that his first task was to allay concerns that his four decades at Exxon had left him too close to Mr. Putin and dictators around the world. So he staked out his turf early in the hearing, arguing that if he had been in office when Russia annexed Crimea in 2014, he would have recommended that the United States provide arms and intelligence support to the government of Ukraine, even though it is not a member of NATO.
“What the Russian leadership would have understood is a powerful response,” he said, casting the Obama administration’s reaction as too weak. His message to the Russian leadership, he said, would be, “Yes, you took Crimea, but this stops right here.”
But Mr. Tillerson dodged a series of questions about whether Exxon Mobil, under his leadership, had lobbied against the sanctions imposed on Russia, which prevented the company from fulfilling huge contracts for oil exploration on Russian territory.
On climate change, Mr. Tillerson said he did not view it as the imminent national security threat that some others did. Although he surprised many in the oil business by acknowledging the dangers of global warming and even embracing carbon taxes, as he did again on Wednesday, he said that much of the literature on the issue remained “inconclusive,” despite the overwhelming consensus of the scientific community about the role of humans.
Mr. Tillerson showed a deep familiarity with many of the most contentious issues in American foreign policy, including the rules governing transactions with the Cuban government and the outlines of the Iran nuclear deal. It was on Iran that he tried to strike a middle ground between Republicans who said the deal should be scrapped — including Vice President-elect Mike Pence — and those who simply call for tougher enforcement of its provisions.
He promised a “comprehensive review” that would include confidential side agreements, largely between Iran and international nuclear inspectors, that have long been a subject of Republican suspicions. But his real complaint about the 2015 accord is that its key restrictions on Iran expire in 2030, and he said he feared Iran would “go back to where they were,” trying to build a nuclear weapon.
At one point Mr. Tillerson complained that there was no provision to keep Iran from buying a nuclear weapon, though later, after a break, he corrected himself to acknowledge that both the Nuclear Nonproliferation Treaty and the Iran agreement itself contain prohibitions on any acquisition of a nuclear device.
Protesters shouted out regularly, interrupting Mr. Tillerson, and he did not look at them, pausing expressionless as they were removed. He told the committee repeatedly that he would not act on human rights abuses, such as the summary executions underway in the Philippines, until he received corroboration, presumably from American intelligence agencies. That inflamed Mr. Rubio, who charged that Mr. Tillerson was ignoring easily verifiable news reports. It also angered Human Rights Watch, the nongovernmental organization that monitors such violations.
“Rex Tillerson’s reluctance to acknowledge human rights abuses by Russia, Saudi Arabia and the Philippines raises serious questions about whether he can effectively serve as secretary of state,” the group said in a statement. “Numerous independent observers, U.N. investigators, media, and humanitarian and human rights groups have published extensive and detailed reporting about the Russian government’s highly problematic domestic human rights record and war crimes in Syria,” and the killing in the Philippines of “6,200 suspected drug users in the last six months.”
Mr. Tillerson said he simply had an engineer’s view of the need for evidence.
Some of the day’s most fascinating moments came as Mr. Tillerson tried to weave a fairly conventional, hard-power view of American influence into a tapestry that clearly rejected some of Mr. Trump’s views. Although the president-elect has said that he doubted the usefulness of the United States-led sanctions against Russia for its incursion into Ukraine, Mr. Tillerson took the opposite view. He said he looked forward to working with the Senate “particularly on the construct of new sanctions” against Moscow in an effort “to cause modifications in Russia’s positions.”
At the same time, in a tense series of exchanges, Mr. Tillerson said he could not say whether Exxon had lobbied against Russia sanctions after the annexation of Crimea, even though the company had submitted filings saying that it was lobbying on the topic. “Let’s be clear,” the company said on Twitter on Wednesday afternoon. “We engage with lawmakers to discuss sanction impacts, not whether or not sanctions should be imposed.”
There were other attempts to separate from positions Mr. Trump took last year. Mr. Tillerson indicated that President Bashar al-Assad of Syria would ultimately have to leave power — the Obama administration’s position — and assailed Mr. Assad’s bombing of civilians. Mr. Trump had talked about allying with Mr. Assad and Russia to fight the Islamic State, even while acknowledging the Syrian leader is “a bad guy.”
Pressed on Mr. Trump’s calls for a national registry of Muslims, Mr. Tillerson said he “would need to have a lot more information around how such an approach would even be constructed.”
Democrats questioned Mr. Tillerson on whether his 41 years at the world’s largest oil company would affect his view of American national interests. Senator Benjamin L. Cardin of Maryland, the ranking Democrat on the Foreign Relations Committee, got to the Democrats’ key critique of Mr. Tillerson, arguing that “having a view from the C-suite at Exxon is not at all the same as the view from the seventh floor of the Department of State,” Mr. Cardin said, referring to where the secretary’s office is.
“And those who suggest that anyone who can run a successful business can, of course, run a government agency do a profound disservice to both,” he said.