LOS ANGELES — The federal act that created public broadcasting is marking its 50th year, but if President Donald Trump has his way it could be a hollow celebration.Trump's 2018 budget proposal makes him the second president to try to kill funding for the Corporation for Public Broadcasting (CPB) and the first to target the National Endowment for the Arts and the National Endowment for the Humanities as well.The White House plan released Thursday, 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.The three agencies combined receive about $740 million annually in tax dollars. It's a sliver of the current $4 trillion federal budget, but it carries outsized importance in political symbolism and, both supporters and detractors say, economic impact.Reaction was swift from the agencies and the art and entertainment world. Alarm was the common thread."We're celebrating the 50th anniversary of the Public Broadcasting Act, what I think has been the most successful public-private partnership — how ironic it would be if we were defunded this year," said Paula Kerger, chief executive for PBS. The nonprofit group's yearly CPB grant pays for programs that are distributed to member stations.The proposal is "counter to the message that American art can reflect society, it can advance society, it can inspire society," said Gina Prince-Bythewood, director of movies including "Beyond the Lights" and co-creator of Fox TV's new drama, "Shots Fired.""It's horrifying to think that can go away, and I have to stay optimistic and believe that (the cuts) won't go through," she said.Kate Shindle, president of the 51,000-strong Actors' Equity Association that represents stage actors and stage managers, said the NEA's $148 million reaps a "return on investment" for both the culture and the economy."The arts are not a frill, a luxury, or some kind of extended vanity project," she said.