Kermit Voice Actor Says Jim Henson's Spirit Has 'Withered' Ahead of New Doc

The former Kermit the Frog actor says he's not hurt he's excluded from the upcoming Jim Henson documentary ... he's hurt 'cause he thinks Jim's spirit within The Muppets is dying.

Steve Whitmire -- who took up the role in 1990 after Henson's untimely death -- tells TMZ ... producers contacted him about the forthcoming documentary "Jim Henson Idea Man" all about the iconic puppeteer a few years ago for home movies he shot dating back to 1978.

Whitmire says he happily handed over the tapes and expected the team to come back around when they were ready to interview him -- after all, he voiced the franchise's most iconic character from '90 until his firing in 2017 -- but, he says no one followed up.

Steve says he's not upset about the studio leaving him out of the doc ... but, he says he is upset because Jim's influence is almost non-existent when it comes to his own creation.

Whitmire says, "It was my defense of the whole of Jim’s influence within The Muppets that ultimately got me kicked out. It doesn’t hurt to be excluded from a documentary, it hurts to see Jim’s spirit, the very spirit celebrated in a documentary such as this, wither unnecessarily."

Basically, SW's saying the life Henson breathed into his character is fading away ... and -- even though Whitmire says he's not bitter about the current state of "The Muppets" -- he does think the show lost something when the company tossed him to the curb.

ICYMI ... Whitmire voiced the character for almost 30 years, including in iconic films like "The Muppet Christmas Carol" and "Muppet Treasure Island," before Disney fired him in 2017.

The company claimed Whitmire exhibited "unacceptable business conduct." Steve maintains he argued over the creative direction of the characters he knew so well, but never disrespectfully.