If confirmed, Mr. Pompeo would be the Trump administration’s second secretary of state in 14 months. In his opening statement, Mr. Pompeo signaled that he planned to harvest a forceful diplomacy.
He said he would take a tough line against Russia and push to improve the Iran nuclear deal through negotiations with European allies so that Mr. Trump could be persuaded to preserve it.
And as planning was underway at the White House and Pentagon for a potential missile strike on Syria for a suspected chemical weapons attack against civilians, Mr. Pompeo, a former Army captain, stressed that “war is always the last resort.”
“I would prefer achieving the president’s foreign policy goals with unrelenting diplomacy rather than by sending young men and women to war,” he said.
Code Pink protesters interrupted the hearing, denouncing what they said was Mr. Pompeo’s support for war.
Two sitting senators and former Senator Bob Dole, the longtime Republican leader from Kansas, introduced Mr. Pompeo to the committee and spoke highly of his credentials to be America’s top diplomat and his commitment to the rule of law.
Mr. Dole, who also introduced Mr. Pompeo during his confirmation hearing last year to be the director of the C.I.A., warmed up the panel, which is far from unanimous in its support to confirm him.
“I can see all you people up there. I can’t see very well, so you look good,” said Mr. Dole, 94.
Senator Richard M. Burr, the chairman of the Senate Intelligence Committee, assured his peers that Mr. Pompeo is transparent and a “natural fit” for the job.
“I asked Mike to lead the C.I.A. in an ethical, moral and legal manner,” Mr. Burr said. “And I’m here to tell you that he did exactly that.”
He asked those on the committee to examine Mr. Pompeo’s nomination on the merits alone.
“If there’s ever one where you put politics aside, this is it,” Mr. Burr said.
Mr. Pompeo caught Mr. Trump’s attention with his broadsides on Hillary Clinton during 2015 congressional hearings about the attacks on a diplomatic compound in Benghazi, Libya, that left four people, including Ambassador J. Christopher Stevens, dead. At the time, Mr. Pompeo was a Republican congressman from Wichita, Kansas.
Mr. Pompeo has been the director of the C.I.A. over the past year, and at least one officer died on his watch.
Mr. Pompeo kicked off his remarks to the panel with a reminder to lawmakers that, as a former congressman, he understands the important oversight role of Congress. He pledged to be in regular contact and work well with the committee — something former secretary of State, Rex W. Tillerson, was not known for during his brief term.
The senators’ insistence that the State Department be on the same foreign policy page as the president referred back to the relationship between Mr. Trump and Mr. Tillerson, who often contradicted each other.
On Wednesday, Mr. Trump said in a tweet that “much of the bad blood” between the United States and Russia “is caused by the Fake & Corrupt Russia investigation.” He was referring to the special counsel inquiry into Russia’s 2016 election meddling and possible coordination with some of Mr. Trump’s associates.
During Thursday’s hearing, Senator Jeanne Sheehan, Democrat of New Hampshire, asked Mr. Pompeo if he agreed with that description of the root of tensions between Moscow and Washington.
He did not. “The historic conflict between the United States and the Soviet Union and now Russia is caused by Russian bad behavior,” Mr. Pompeo said.