LONDON — The Guardian, the British newspaper that won a Pulitzer Prize for its coverage of national security leaks in the United States but whose aggressive international expansion has brought heavy losses, switched to a tabloid print format on Monday as part of efforts to cut costs.

The newspaper’s shift comes with the British journalism industry in a state of flux, as declining advertising revenues have forced various storied publications to make major changes, from firing hundreds of journalists to shutting down print operations entirely. The challenges mirror many of the difficulties faced by legacy publications the world over as they attempt to transition to more digitally savvy operations.

The Guardian had long been a standard-bearer in Britain for that shift. The left-wing publication focused on courting vast numbers of readers around the world, and it hired dozens of reporters in the United States and Australia in particular. It has ardently refused to set up a paywall — the preferred strategy of many of its rivals, from The Times of London to The Wall Street Journal and The New York Times — opting instead to ask its readers for donations, even setting up a nonprofit arm to help fund its journalism.

For a while, that strategy appeared to bear fruit. The Guardian shared a Pulitzer Prize with The Washington Post in 2014 for coverage of documents leaked by Edward J. Snowden, the former National Security Agency contractor. That a British newspaper won a prestigious award that had largely been the domain of American publications illustrated the scale of its ambition.