Success has not spoiled Rodney Dangerfield, nor custom staled, nor age withered him. Well--two outta three ain't bad. Misery, of course, still loves his company. "I tellya, with me, nothing comes easy," says Dangerfield from Fort Lauderdale, where he is appearing on the stage and on the beach, and in a hotel room with his faithful traveling companion, a hot plate.

Laugh, and the world laughs with you. Cry, and--if you are Rodney Dangerfield--the world laughs at you.

With Dangerfield, it's always the "Why Me?" Decade. He is America's favorite mal vivant, the Mozart and Leonardo of self-depreciation. He is our foremost national joketeller.

The man who has built a career on getting no respect has to admit, when his back is to the grindstone, that things do seem to be going his way. There's even evidence he has become a cultural icon. The Smithsonian Institution, no less, recently acquired from Dangerfield one of his distinctively dull red ties and one of his definitively dull white shirts to be placed on display in one of its museums. "I still don't get no respect--they took the shirt off my back!" Dangerfield says.

And tonight on ABC, Dangerfield gets his first prime-time network special, "It's Not Easy Bein' Me," at 10 on Channel 7. Not even this came easy, though. The special was taped in August, scheduled for November, rescheduled for February, and is now finally being shown as part of ABC's May sweeps effort. Dangerfield says he doesn't understand how the minds of network executives work. If he ever does start understanding that, he will be in big trouble.

"I guess they have their own system," sighs Dangerfield with his usual devil-may-care desperation. It must be admitted that the show is not consistently funny. Sometimes, for instance, it's hilarious. And sometimes it is almost UNBEARABLY AMUSING.

On the show we first see Baby Rodney in his crib, where he's swaddled in togs that naturally include the inescapable red necktie, and hear more of his laments against a cruel and indifferent fate. Actually not so much indifferent as vicious. "One time I took out a belly dancer," Dangerfield says during his monologue. "She told me I turned her stomach."

This is a man who, he reports, doesn't just have ringing in his ears. He gets busy signals.

The special includes a spoof of "The Mikado" that Dangerfield wrote himself; a very funny superhero sketch with Bill Murray and Dangerfield bouncing off each other and flying around a room (Valerie Perrine is the heroine); a visit to Dominick's, "a tough joint" where they still play songs like "The Too Fat Polka" and where a young Dangerfield is given the professional advice, "You shouldn't sweat so much"; and a trip to Dangerfield's psychiatrist (Murray) who, when this patient shows up, buzzes his secretary to say, "I'll take all calls."

If there's a problem with the program, it's that it's too tight; too much was nervously crammed in, and so there's not much room to breathe. And it was probably not necessary to interpolate Dangerfield into every second of it, like Aretha Franklin's rendition of, logically enough, "Respect," wherein Dangerfield appears as a freakish backup singer. But these are minor quibbles about a program that is--well, let's come right out and say it without equivocation--quite good under the circumstances.

No, really, it's a masterpiece. As a great moment in the life of American television, it's right up there with the Camaro commercial, "The People's Court" and the Claus von Bu low trial. And funny. Whoa boy.

"Everyone seems to like it," Dangerfield mopes jauntily. "Yeah, I'm pleased with it. The network asked me to do a couple more, so, maybe it'll be okay, I don't know." For Dangerfield, this is about as close as you get to bravado.

Other things are bubbling for him. This summer, he'll spend eight weeks in Chicago making "Easy Money"--that is, a new film by that title. Then, in the fall, he'll go to Universal to play the W.C. Fields part in a remake of "My Little Chickadee," with the woman who takes the Mae West part still to be chosen.

"I don't know what more I can do. What more can I ask? I'm in show business, I guess," Dangerfield says. He is asked if all this success has changed him. "Are you kiddin'? You're the same guy no matter who you are. I spent three-quarters of my life worrying about money. You are what you are, you know? I'm supposed to change now--have four guys drive me around in Cadillacs? Forget it, willya? I'm still the same guy."

He doesn't even own a car. On his last birthday, Estelle Endler, his longtime publicist and executive producer of the special, said to him, "What can you give a man who has nothing and doesn't want anything?"

But he doesn't have the same schedule he used to have, and that means fewer appearances than before on the Carson show, a big disappointment for those of us who await those appearances as eagerly as we await a fresh shipment of Mallomars. But Dangerfield says each Carson gig requires him to come up with 35 to 40 new jokes, and that means trying out 2,000--to find the ones that are funny. It's not easy being him.

"No one knows what someone else goes through for what they do," says the philosophical Mr. Dangerfield.

The Smithsonian's request came as a pleasant surprise that has clearly not overwhelmed him. "It is very flattering, I guess. But I'm 60 years old, so I can't do cartwheels." He's not sure what the Smithsonian will be doing with the tie and shirt. "They'll put 'em in there somewhere, so when I'm dead, they'll remember, huh?"

Such a ray of refracted sunshine he is. Such a breath of polluted fresh air. Dangerfield, you are a genius, of sorts, and, no kidding, you contribute to the quality of life. Tell us a joke.

"A joke? Let's see. Well--I'm gettin' old, you know. Old. I'm at the age now, when I go to parties, I swap thoughts." He waits for something of a laugh. "Just wrote that one yesterday," he says. "So what can I tellya?"