The emergence of Netflix and other streaming services that offer subscribers a commercial-free TV viewing experience means a generation could grow up without ever knowing the meaning of the phrase: “we’ll be right back after a word from our sponsor.”

The broadcast and cable networks that took in $19.7 billion for advanced sales of commercial time last year don’t want to see that happen. That’s why Fox and NBC plan to reduce the amount of commercial time in their shows starting next fall. Both are looking to offer advertisers the chance to run commercials in shorter breaks during which they might reach a more attentive audience. Other media companies have begun similar initiatives to reduce the number of commercials on their cable channels.

But doing so comes with a risk. Airing fewer commercials could mean less revenue for the networks, unless they can convince advertisers that it’s worth it to pay more to have their spots running in a less-cluttered program. The topic is being debated ahead of the upfront market, where most of the advance ad time for the 2018-19 TV season is sold.

The TV networks need a new selling strategy as their ratings continue to decline. The prime-time audience of the broadcast networks is off nearly 20 percent compared with the previous year and many of the major entertainment cable networks have experienced double-digit declines as video content is seen more on digital platforms.

Fewer commercials could help reverse that trend and advertisers would welcome a less crowded environment for their messages.

Broadcast networks’ hourlong prime-time shows carried an average of 11 minutes and 32 seconds of national ads in the fourth quarter of 2017, about the same as four years earlier, according to data from media strategy firm Magna Global. Clutter is seen as a larger problem on cable networks, some of which carry as much as 18 minutes of national advertising per hour. That has led Turner, Viacom and A&E to announce they are cutting the ad load on some channels by as much as 50 percent.