NPR Music also will produce two-hour radio specials at the two festivals for member stations.
The venerable folk festival - best know as the place where Bob Dylan went electric in 1965 - runs Friday through Sunday. The jazz festival, headlined by Aretha Franklin, Herbie Hancock and Sonny Rollins, is set for the following weekend.
Bob Boilen, host of the NPR Music program "All Songs Considered," said the initiative was a way to reach far more fans than can attend the concerts.
He also said it was a reflection of the excitement surrounding this year's folk festival, which boasts an eclectic lineup of artists that transcend the confines of traditional folk, such as Brian Wilson of the Beach Boys, Trey Anastasio, the Black Crowes, Jimmy Buffett and reggae performers Stephen and Damian Marley.
"Newport's trying something different this year," Boilen said. "It's a good start, and I think it's a good idea for us to be on the ground floor."
On Saturday and Sunday, NPR plans to webcast performances by Jim James of My Morning Jacket, Jakob Dylan, Richie Havens, the Cowboy Junkies, Steve Earle, Brandi Carlile and others. The concerts also will be broadcast live on member station WFUV-FM in New York City.
NPR and festival organizers said Wednesday they were still working on enlisting the festival's biggest stars, such as Anastasio and the Marleys.
Anya Grundmann, executive producer for NPR Music, said Buffett and indie singer-songwriter Cat Power were the only performers so far that were not planning to participate in the webcasts. But she said NPR had also not set out to get each and every artist involved.
Select acts from the jazz festival also will be webcast, as well as be broadcast live on WBGO-FM in Newark, N.J.
Ian Zaider, an executive vice president at The Festival Network, the production company newly in charge of the festivals, said he considered the relationship with NPR a good fit because of the overlap in audiences for public radio and the jazz and folk concerts.
"It really enables us to extend this experience globally, which bodes well for our attempts to brand the festival and really share these extraordinary performances on a worldwide basis," he said.
