Many of those stations are in rural and underserved areas, she said, with residents who either don't have access to cable or satellite or can't afford it and who rely on over-the-air broadcasting.
Kerger, who addressed the issue at a TV critics' meeting, said observers have speculated, hopefully, that because PBS has survived previous funding threats, "'You'll be okay, right?'"
But she's forced to assume that anything can happen in what has been "an extraordinary year on so many levels," Kerger said. "We need to be quite vigilant as Congress debates our funding that we don't assume people remember the impacts we have on communities."
There's an irony that this potential existential crisis for some public TV stations comes as the 50th anniversary of the Public Broadcasting Act approaches in November, Kerger said. The 1967 act created the Corporation for Public Broadcasting, which provides grants to about 1,500 locally owned-and-operated public TV and radio stations nationwide.
She's taking the threat seriously and said that others in public media, which includes National Public Radio, are linking arms "to try to make an effective case" for federal funding, Kerger said. But more voices need to be heard as Congress weighs Trump's proposed spending plan that would trigger a move toward elimination of all federal support, she said.
At the end of the day, "What legislators most care about is impact on their own communities," Kerger said, encouraging people nationwide who care about public broadcasting to let their representatives know.
Trump's 2018 budget proposal isn't the first to try to cut funding for the Corporation for Public Broadcasting. But it is the first to also propose gutting money for the National Endowment for the Arts and the National Endowment for the Humanities.
The three agencies combined receive about $740 million annually in tax dollars. That's a sliver of the current $4 trillion federal budget. But the federal funding for the agencies carries outsized importance in political symbolism and, both supporters and detractors say, economic impact because of the private dollars it attracts.
Asked about critics who consider PBS a fount of liberalism that doesn't warrant public funds, Kerger replied that surveys conducted by Democratic and Republican pollsters for PBS found an overwhelming level of support among people of all political stripes for its continued federal funding.
The cost works out to about $1.35 per citizen per year for programming that can't be found elsewhere on TV, Kerger said, including educational shows for children and documentaries such as Ken Burns' upcoming documentary series on the Vietnam War. Other support is provided by private and corporate donors.
Burns, speaking to critics Sunday about The Vietnam War, debuting Sept. 17, also addressed the funding issue. Given the "miniscule" amount of the federal budget that goes to public broadcasting, he said, arguments against it represent "ideological footballs" and misunderstandings.
"People assume that we're there for Nob Hill and Beacon Hill, when, in fact, some of our best ratings are in Alaska and the Arkansas... or West Virginia or Oklahoma. This is really who we're talking to," Burns said. "And we're trying so hard as a network to reach out to all Americans with a brand that they can feel comfortable with."
The White House budget plan, which emphasizes military and other security-related spending and slashes many domestic programs, is the first step in a lengthy budget process that ultimately requires Congressional approval.
Given that the House is in recess and the Senate will be, PBS said the next likely window for action will be September.