An earlier version of this article incorrectly suggested that Dutch Harbor will rely on the Senate infrastructure package to get connected to fiber Internet. Alaskan telecom company GCI has already received federal funding to build a fiber link to the region and is carrying out initial work.

If the bipartisan infrastructure package that passed the Senate on Tuesday becomes law, many of the nation’s most remote communities might finally get connected to the Internet through fiber-optic cables, helping fix their spotty Web links.

But rural telecom companies say even fiber links won’t fix another big communications problem in their communities — a lack of cellphone towers that leaves many residents and first-responders with extremely poor mobile service.

The local cellular provider in one of Alaska’s busiest fishing ports, Dutch Harbor, has patched together 4G cellular service for the port itself, a settlement of 4,500 people in the Aleutian Islands. But many smaller communities in the region have no wireless coverage, or outdated 2G or 3G service, said Emmett Fitch, the company’s chief executive.

“Let’s totally build fiber to every single home. I’m totally 100 percent behind that. But at the same time, let’s not forget that we’re going to need the wireless infrastructure there, too,” Fitch said in a phone interview from Dutch Harbor, which lacks fiber Internet. Alaskan telecom company GCI has pledged to build a fiber link to the Aleutian Islands and is carrying out initial work on the project.

Fitch was speaking with a brief time delay over a satellite link that connects the town’s mobile network to the rest of the world.

Small telecom companies in rural Idaho and South Dakota share that view, as do first-responders in a remote corner of Washington state. Now that the Senate has passed the bill, cellular carriers plan to turn their advocacy efforts to the House, with the hope of gaining more funding for mobile connectivity, said Gwen Donaldson, a political consultant who is representing a coalition of cellular companies.

Their concerns underscore the complexity of modern communications networks, which require steep spending to dig the ditches, lay the cable and build the cellular towers to connect far-flung communities. In the most rural areas, it’s the sort of investment few companies are willing to make, because there are few potential customers to help recoup costs.

Proponents of the infrastructure bill say that the legislation cannot fund every need and that it still represents the largest federal investment in broadband Internet to date — $65 billion.

“This historic investment will extend the promise of high-speed broadband to students, workers, farmers, and small businesses across the country, driving opportunity, transforming communities, and allowing millions more people to fully participate in modern American life,” Sen. Michael F. Bennet (D-Colo.) said last week. He helped advocate for the provisions, along with Sens. Angus King (I-Maine) and Rob Portman (R-Ohio).

The centerpiece of the plan would provide $42.5 billion to states to award grants for the construction of broadband links to homes, schools and businesses in regions with poor service, including rural and urban areas. Grant recipients would need to build connections at speeds of at least 100 megabits per second for downloads and 20 megabits per second for uploads, rates that only fiber-optic connections can steadily supply, experts say.

Fiber cables buried underground are widely considered the gold-standard method of providing Internet connection. They offer the fastest, most reliable service, and aren’t disrupted by storms or hilly terrain, which can interfere with the cellular signals that transmit Internet links wirelessly in some rural areas without fixed-line connections.

And once the cables are in the ground, the capacity of the data they carry can be dramatically ramped up over time.

Advocates for fiber say it must be the focus of federal spending.

“Of 38 OECD countries, the U.S. ranks 30th in penetration of fiber,” said Susan Crawford, a Harvard Law School professor and expert on technology policy. “How much do we, as Americans, value having everyone on the same playing field with the rest of the world?”

She likened the need for federal fiber spending to the government push under President Franklin D. Roosevelt to connect rural U.S. homes to electricity.

“In the [1930s], the farmers did not have electricity because for the private providers it didn’t make sense to run wires to them,” she said. “We are in exactly the same story now when it comes to high-speed Internet access.”

Fred McLaughlin, chief executive of Standing Rock Telecom, a cellular service provider owned by the Standing Rock Sioux tribe, said that sort of fiber investment would greatly benefit his community, which stretches across a sparsely population strip of North and South Dakota.

But these days, many young people do most of their Web surfing and Internet connecting through mobile devices, not through a fixed-line connection, he said, and for that, stronger cellular infrastructure is needed. With more federal subsidy, Standing Rock, he said, could erect more towers to beam signals to more corners of the tribe’s territory, which roughly equals the size of Connecticut.

First-responders in his region also desperately need better mobile service. “If there’s a prairie fire, yes, their two-way radios will work, but to get location and pictures to be sent they will have to send [the data] later, which will cause a safety issue,” he said. “We want to ensure we can cover all roads on the reservation, even the dirt roads.”

Firefighters and emergency-medical services in rural Washington echoed that view. Jason Edwards, a volunteer first-responder in Stevens County in the northeastern corner of the state, said about two-thirds of his district has no stable cell coverage.

“On a day-to-day basis, the lack of cell services is one of the biggest things affecting us,” he said. People involved in car accidents can’t always reach an ambulance, he said. And EMTs who respond to medical emergencies sometimes can’t phone a hospital to seek advice.

“We might need to find a house with a landline or do what we can over the radio, but we can only talk to our dispatchers, and they’re not medical experts,” he said.

Mike Bucy, a fire chief based in Loon Lake, Wash., said the lack of cell service has been frustrating this summer as firefighters battle some of the worst blazes in years. They can’t always send the latest information to the public, call in extra resources, or exchange updates with neighboring firefighting forces, he said.

Better communications for first-responders is an issue in rural Idaho, too, says Chip D’Amato, executive vice president of Inland Cellular, a wireless telecom company in Lewiston, Idaho, about 140 miles south of Loon Lake. First-responders usually direct their pleas for better communications to his company “because it’s our community,” he said.

Angelina Panettieri, a technology and communications expert at the National League of Cities, a nonprofit organization representing the views of municipal governments, said at least part of the broadband funding will definitely help cellular providers.

Of the $65 billion, about $2 billion is set aside to finance construction of “middle mile” networks, which she said could be used to extend a fiber link from a highway out to a cellular tower.

“Something I know a lot of wireless carriers say is, if you want to build wireless, you need a lot of wires,” she said. “A robust fiber network will support … good mobile connectivity.”