Transportation Secretary Pete Buttigieg got a close-up look at the crumbling state of New York City’s most critical rail link on Monday and vowed that the Biden administration was committed to getting a new train tunnel built under the Hudson River.After touring the decaying 110-year-old Hudson tunnel in an Amtrak car crammed full of elected officials from New York and New Jersey, Mr. Buttigieg sounded convinced of the urgency of completing a second tunnel. The long-delayed project, with an estimated cost of $11.6 billion, is vitally important to the national economy, he said at a news conference in Pennsylvania Station in Manhattan.

If one of the two tubes of the 110-year-old tunnel had to be closed for repairs, “you would be feeling the economic impact all the way back in Indiana, where I come from,” Mr. Buttigieg said. “That’s how important this is.”

The Biden administration’s embrace of the project — known as Gateway — is a sharp reversal from the Trump administration’s obstructionist stance

Aboard the train, Mr. Buttigieg rode alongside Senator Chuck Schumer of New York, the Democratic majority leader, who said the infrastructure package that President Biden negotiated with Republicans last week included enough money to cover the federal share of the tunnel’s cost.

“Now we can announce that the hostage that was the Gateway tunnel under the previous administration has been freed,” Mr. Schumer said. “We are full speed ahead to get Gateway done.”

Still, the region’s tormented commuters may skeptically state that they have heard this all before. They have.

A new tunnel has been planned, in one form or another, for more than a quarter-century. In all of those years, promises have been made and broken, federal funding has been lined up and then surrendered.

In 2015, the Obama administration deemed Gateway one of the most important public works projects in the country. On Monday, Mr. Schumer said it still was.The project was aimed at relieving overcrowding on trains going to and from Penn Station, the nation’s busiest transit hub. The station and the tunnel, both of which are owned by Amtrak, had been pushed far beyond their intended capacities more than a decade ago. Then Hurricane Sandy blew through the region in 2012 and pushed millions of gallons of salty water into the tunnel.

The insides of the tubes have been deteriorating faster since then, causing Amtrak officials to fear that the tubes would have to be taken out of service one at a time for an overhaul.

The loss of one of the tubes, even temporarily, would reduce the number of trains that could reach Penn Station during the morning rush by 75 percent, crippling the daily commute for the 150,000 passengers who rode every weekday between New Jersey and New York before the pandemic.

Even after the coronavirus pandemic kept most commuters home for more than a year, the number of trains that Amtrak and New Jersey Transit, a commuter railroad, run through the tunnel each day is not much lower, said Brian Fritsch, manager of the Build Gateway Now Campaign at the Regional Plan Association, a research and policy group.

Mr. Fritsch said train ridership in the region is rising and approaching 50 percent of prepandemic levels. “It’s returning a little bit faster than they had anticipated,” he said, adding that he was pleased to see “a renewed sense of urgency that this should be a top priority of the Biden administration.”

Still, in the last several years, only modest progress has been made toward the completion of Gateway. The construction of one of its components, the replacement of a 110-year-old swing bridge that carries trains to and from the Hudson tunnel, is expected to begin within a year.