PUBLIC LIBRARIES can be sanctuaries, gateways to discovery and temples of learning. They are vital institutions, promoting the health of democracy. To that end, among the more troubling trends in recent years has been the decreased funding for libraries across the country. Faced with budgets in perpetual decline, cities including Detroit and Denver have taken to shutting down branches and laying off library staff. Libraries in the Washington area, too, have had to cope with lean budgets.

To confront this bleak reality, the Fairfax County library system implemented a “strategic plan” last fall, a proposal that embraces a smaller budget by reducing staff, getting rid of master’s-degree requirements for branch managers and forcing children’s librarians to prioritize developing new reading programs over staffing branches. As The Post’s Tom Jackman reported, the Fairfax system also recently adopted a new “floating collection” system that, in theory, streamlines costs and promotes efficiency.

Under this policy, books and other library materials don’t have a permanent branch; they stay where they’re returned, which means the costs — not to mention the wear and tear — from shuttling them between library locations are significantly reduced.

While those are worthwhile objectives, the problem with the floating collection system is how it reviewed books for discard. Every public library system periodically discards damaged or out-of-date materials or to make room for new items — in Fairfax County’s case, about 20,000 items a month. But volunteer organizations typically sift through those piles to find books suitable for donation or sale to homeless shelters, prisons or hospitals.

In Fairfax, however, discarded books were sent directly to the library’s technical operations center in Chantilly, and volunteer groups had no influence over which were reused or thrown out. In the months since the program’s introduction, some 250,000 books — more than a few of them in decent condition — were destroyed. Only around 3,000 were sent back to the volunteer groups.

Those books belonged to the taxpayers who bought them. Library patrons and county officials were understandably outraged. Thankfully, the library’s Board of Trustees listened to the hundreds of protesters who gathered in Annandale on Wednesday night: It suspended the program until more community outreach could take place. As the digital age races on, libraries will inevitably have to change. But that doesn’t have to mean throwing out a quarter-million books just because they seem worn.