Jim Henson slips his right hand into what could be mistaken for a big green sock and with that, Kermit the Frog is brought to life.

"Ta-dahhh!" says kermit.

He's an easygoing frog - one of the all-time great frogs, as a matter of fact - and the man behind him seems easygoing too. But together they have turned a Hyattsville high schooler's hobby into an enormous and lucrative enterprise: The Muppets, a master race of funny, fuzzy, furry creatures whose great fame came as the stars of public television's landmark "Sesame Street" series.

Now, Kermit has his own program - "The Muppet Show" - on 130 U.S. TV stations and sold for telecast in 36 other countries. In Washington, Channel 7 airs it at 7 p.m.

Kermit, whose sewn-on eyes cannot blink, is asked if fame has gone to his flannel head. The answer would seem to be yes. "I'm the star," he declares unblinkingly. "There's only one star frog." oh? And perhaps he'd like to do the whole show by himself. "I could, but the rest of the guys need work," he says.

The rest of the guys are doing fine, although at this particular moment, in Henson's upper East Side workship, they aren't quite themselves. The dismantled yellow torso of Big Bird is sitting in one culttered corner. Bert and Ernie are propped up on a table, speechless and lifeless. And a frog that looks suspiciously identical to Kermit sits on a stand with a large pin through its head.

"Actually, there are quite a few Kermits," Henson explains, casually slaughtering an illusion. "Well, then," he is asked, "which one is the real one?"

"They're all the real one," he says.

Kermit is host of "The Muppet Show," now completing its first year in syndication and already renewed for next year by the five CBS-owned stations. Henson tried for years to interest the network in a prime-time Muppet show, but they wouldn't buy it. So, in most markets, he's in what's called "prime access" time, 7:30 p.m. One ratings service recently named "Muppet" the No. 1 syndicated access show.

For "Sesame Street," Henson Associates Inc. (letterhead: "ha") is contracted by the Children's Television Workshop (CTW) to supply characters and to split profits from the licensing of "Sesame Street" merchandise, of which there is solenty. Neither party in this is wants to discuss the financial arrangements. A CTW spokesman declined to cite figures: so did a Henson executive. We're a success, but we never discuss figures at all," he said.

Henson is 6-feet-1, thin and bearded, and has a softspoken and calm sort of countenance that reportedly never cracks. "It's eerie," art director Michael Fritch says of him, jokingly. "In 10 years he'll probably turn out to be an ax murderer." Henson also has that preoccupied air one associates with scientists and cartoonists. Asked his age, he at first replies. "I'm 40," then stokes his beard and says, "or 41," looks into the air for a moment and after a pause decides, "uh, 40."

Kermit is 21 year. He was born two years after Henson created The Muppets while a high-school student in Hyattsville, Md. In 1955 he auditioned for a spot on a WTOP variety show, lost the job soon after he got it and went to WRC, where he and The Muppets appeared daily for eight years. Henson also did hundreds of local commercials during the '50s and early '60s, the best-remembered probably being for Wilkin Coffee. There were these two creatures, one of whom drank the coffee and one who did not. The one who did not always met terrible fates, only to return again.

Originally, "Muppet" meant a combination of marionette and hand puppet (one version of Kermit has moveable arms on sticks manipulated from beloe). The species has expanded though, to include the likes of Big Bird, who is a combination of a human being and a Big Bird costume. "The characters are never based on people we know," Henson says. "They're based on a personality type or an attitude more than anything else.

"Kermit is the closest one to me. He's easiest to talk with. He's the only one who can't be worked by anybody else, only by me. See, Kermit is just a piece of cloth with a mouth piece in it. The character is literally my hand." About two dozen puppeteers help Henson operate the other Muppets. On "The Muppet Show," tape editing and canned audience laughter and applause help heighten the illusion.

In other words, it's all a fake, but a pretty beguiling one most of the time.

The Henson workshop is not what would qualify as a jolly place - not, say, like Santa's - but also lots of bright colors on and a general aura of utter disarray make it obvious this isn't IBM , either. Henson enters the workshop, down the street from his cozy office, with a "Hi, guys," and strolls from table to table to see what's going on.

"Well, I've got this mouth here," says one young man, flapping a polyfoam mouth at Henson. A fox wearing glasses sits on another table, near the disembodied head of a mole. Many of these characters are being made for a network Muppet special to air next Christmas.

With another worker Henson discusses the construction of a prop apple pie that can be eaten by the Cookie Monster without getting gunk all over the puppet. Slices of foam rubber turn out to look just like apples - but only on television.

"Everything we build is built for television," Henson explains, "we always work to a television monitor. Television gives the characters life. That really don't work in person." That's part of the reason for Henson's success. The Muppets are more stylized and less detailed than traditional puppets, yet they have a freedom of movement that is definitely revolutionary.

Henson says he isn't bothered by imitations of The Muppets. He doesn't seem to be bothered by anything nor to be dazzled, either, by his growing success. Recently he accepted an award for The Muppets as "Special Attraction of the Year" on the CBS "Entertainer of the year" special. But not everything The Muppets have done was a hit. Their participant in "NBC's Saturday Night" last year was more of a drag; the bits were rarely very funny and they tended to fizzle. Henson doesn't know why.

"It's not an easy thing to analyze," he says. "I still like the show. But they'd write lovely, far-out things for themselves and square, dull nothingness for our characters." As on "Sesame Street," Henson was at the mercy of other writers. On "The Muppet Show" he is contributing writer as well as producer.

But it's never really been pets loveable anyway; many of the jokes on "The Muppet Show" are antique wheezes. What makes the Muppets work is their delivery, their appearance and the range of expressions the puppeteers get out of them.

Henson have five children of his own and they audition some of the Muppet routines, he says. He is married to Jane Nebel his fellow puppeteer in the early days in Washington when you could count the number of Muppet on one hand and work them all with four.

In one of the workshop rooms, ace techinician Faz Fazaki is about to put Emmett the Otter through his paces. Enmett is only a wooden skeleton with funny arms now, sitting in a model rowboat on top of a suitcase. But Fazaki begins to play with a remote control device and Emmett begins to seem to row the boat.

Henson's eyes light up. "Oh, I love this thing," he says, and you can tell from the look on his face that he is still, in part, the child who never had to give up toys.