The biggest U.S. cable-TV channels are experiencing a troubling trend: Their reach into American households is shrinking.

Over the past four years, the top 40 most widely distributed channels in 2010—household names like CNN, ESPN and USA—have lost an average of 3.2 million subscribers, or more than 3% of their distribution, according to a Wall Street Journal analysis of data from measurement firm Nielsen.

Some in the industry point to consumers who are “cutting the cord,” ditching their cable and satellite-TV connections in favor of more affordable online video options like Netflix and Hulu. But the numbers don’t add up. Last year the pay-TV industry lost 166,000 subscribers, according to research firm MoffettNathanson LLC. While that was the first annual decline on record, it isn’t enough to account for the subscriber declines of the biggest cable channels.

Indeed, the data and interviews with a range of cable-TV industry executives suggest that something else is going on: Many consumers aren’t so much cutting the cord as shaving it.

A growing share of pay-TV customers are signing up for smaller, cheaper bundles of channels that cost anywhere from $10 to $50 a month and don’t include popular channels like TNT, USA, ESPN, CNN, Fox News, Disney Channel and Discovery Channel, the industry executives say.