SHANKSVILLE, Pa. — The two presidential contenders put their acrimonious political sparring on hold on Friday to pay their respects to the Americans killed in the Sept. 11 terrorist attacks, a pause in an extraordinarily polarizing race in which the candidates have offered drastically different visions on virtually every issue, including what it means to comfort a grieving nation.

President Trump offered somber remarks in Shanksville, Pa., honoring those who died on Flight 93, the plane that was hijacked and headed for Washington but instead crashed into a field after passengers fought back. Joseph R. Biden Jr., the Democratic nominee, traveled to New York before visiting Shanksville to commemorate the 19th anniversary of the attacks, speaking with family members of the victims but not making a formal address.

“Our sacred task, our righteous duty and our solemn pledge is to carry forward the noble legacy of the brave souls who gave their lives for us 19 years ago,” Mr. Trump said. At another point, he added, “The only thing that stood between the enemy and a deadly strike at the heart of American democracy was the courage and resolve of 40 men and women — the amazing passengers and crew of Flight 93.”

Mr. Biden and his wife, Jill, attended the National September 11 Memorial & Museum’s commemoration ceremony in Lower Manhattan, standing with Gov. Andrew M. Cuomo of New York for much of the time. Then the Bidens traveled to Shanksville, where Mr. Biden laid a wreath of white flowers at the Flight 93 National Memorial and met family members of some of those who died. (Mr. Trump, during his morning visit there, also laid a wreath of white flowers in front of the wall of names, but he did not meet with any family members.)

“One of the marks of being an American is understanding there are some things that are bigger and more important than yourself,” Mr. Biden said in Pennsylvania. He marveled at those who “consciously know that what you’re about to do is likely to cost you your life.”

Earlier in the day, Mr. Biden, the former vice president, promised reporters that he would not “talk about anything other than 9/11.”

“We took all our advertising down,” Mr. Biden, clad in a black mask, said early Friday morning at the airport in Delaware. “It’s a solemn day. That’s how we’re going to keep it.”

ImagePresident Trump and his wife, Melania, observed a moment of silence on Air Force One as they traveled to Shanksville.
Credit…Erin Schaff/The New York Times

Mr. Trump avoided reporters shouting questions as he boarded Air Force One. On the plane, he followed directions when his chief of staff, Mark Meadows, told him that an announcement would play on the P.A. system when it was time to observe a moment of silence at 8:46 a.m., when the first plane struck the World Trade Center’s north tower. “God bless America,” Mr. Meadows said after the moment of silence had passed. “God bless America,” Mr. Trump echoed. He offered no further remarks.

The appearances marked a sharp departure in tone from a week of intensifying hostilities between Mr. Biden and Mr. Trump, with Election Day less than two months away. The Democrat said on Wednesday he held the president responsible for the scale of the coronavirus deaths, following new revelations from a forthcoming book by the journalist Bob Woodward that Mr. Trump knowingly minimized the risks of the virus. Mr. Biden has also blasted the president over reports that Mr. Trump disparaged American soldiers killed in combat and other veterans, which Mr. Trump denied.

The president, for his part, kept up an onslaught of scathing and sometimes false claims about Mr. Biden over issues from trade to his approach to America’s suburbs. In rallies, tweets and press briefings, he attacked the former vice president as a hostage of the Democratic left who would preside over a lawless nation. And by later on Friday afternoon, Mr. Trump was back to tweeting combatively at Democrats.

As the Bidens went to New York, Mr. Trump and his wife, Melania, traveled to the memorial service in Shanksville in the morning. There, he delivered remarks from a lectern set up in front of the wall of names commemorating the 40 passengers and crew who were killed on the flight.

“In their memory, we resolve to stand united as one American nation,” Mr. Trump, flanked by teleprompters, said in his speech. “To defend our freedoms, to uphold our values, to love our neighbors, to cherish our country, to care for our communities, to honor our heroes and to never, ever forget.”

He also made a point to reference his own record on confronting terrorism, and he made frequent nods to law enforcement.

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Credit…Amr Alfiky/The New York Times

Vice President Mike Pence and his wife, Karen, also attended the ceremony in New York, and he chatted with Mr. Biden, trading an elbow bump in lieu of a handshake, a nod to the pandemic. The Pences later attended another ceremony nearby, and they also stopped at a firehouse. The Bidens did the same in Pennsylvania, bringing cake and beer to a Shanksville fire station.

Mr. Biden’s running mate, Senator Kamala Harris, and her husband, Douglas Emhoff, attended a remembrance ceremony in Fairfax, Va.

Mr. Biden, who has suffered a series of family tragedies, is perhaps at his best when comforting others grappling with grief, whether in a one-on-one conversation or while giving a eulogy, and amid the coronavirus crisis has made a point to frequently recognize the staggering death toll. Mr. Trump, a lover of large campaign rallies, is not known for those skills and has often glossed over the devastation of the virus.

In New York, Mr. Biden gave flowers to a 90-year-old woman who said she had lost her son, as Mr. Biden sought to empathize about pain that, he suggested, “never goes away.” To her and in Pennsylvania on Friday, he mentioned his own son, Beau Biden, who died of brain cancer in 2015 and had previously deployed to Iraq with the Delaware Army National Guard.

“It takes a lot of courage for someone that lost someone to come back today,” Mr. Biden said at another point in New York. “It’s a wonderful memorial, but it’s hard. It just brings you back to the moment it happened, no matter how long, how much time passes. So I admire the families who come.”

In Pennsylvania, he again talked about the grieving process with the family members on hand and engaged in some lighthearted banter with younger attendees.

Mr. Trump’s condolences were more scripted.

“The first lady and I come to this hallowed ground deeply aware that we cannot fill the void in your heart or erase the terrible sorrow of this day,” he said. “The agony renewed, the nightmare relived, the wounds reopened, the last treasured words played over and over again in your minds. But while we cannot erase your pain, we can help to shoulder your burden.”

While Mr. Trump and Mr. Pence have engaged in campaign travel for months, Mr. Biden has only recently begun to travel more frequently, and Friday was another example of his stepped-up schedule of in-person appearances. He visited Pennsylvania and Michigan earlier in the week, and he is scheduled to travel to Florida, Pennsylvania and Minnesota next week.

The annual Sept. 11 ceremony at ground zero ended up being a heavily scrutinized moment in the last presidential race, as Hillary Clinton left abruptly and had to be helped into a van, a scene that was captured on video. Mrs. Clinton had received a diagnosis of pneumonia two days earlier, but her campaign did not disclose it until hours after she left the ceremony.

Annie Karni reported from Shanksville, Katie Glueck from New York and Thomas Kaplan from Connecticut. Maggie Haberman contributed reporting from New York.