When he was 12 years old, Ron Fields almost cracked up watching "It's a Gift" on TV. He was laughing so hard he had to leave the room.

"Wow," he said when he had recovered. "W.C. Fields has to be the funniest guy in the world."ir,10p

His older sister turned to him casually.

"He's your grandfather, you know."

Well no, he didn't know. His five older brothers and sisters had forgotten to tell him. Everyone assumed he already knew.

It turned into a career.

Tonight at 10 Channel 26 will air "W.C. Fields Straight Up," a two-hour review of the great comedian's life and work, rich with clips from his films, even some of the old silent ones, and you don't have to be family to crack up. Ronald Fields, who collected the clips and helped write the xr script, will appear on the program. (Preview on Page B6.)

He had just got out of Loyola University in his native Los Angeles and was scraping up a living by writing short stories -- "$250 for six weeks' work" -- when his agent learned who Fields' grandfather was.

"The agent told me if I didn't write the book someone else would," he said on a visit here this week. "So I did. It was a best seller."

That was in 1973. "W.C. Fields by Himself" consisted mainly of W.C.'s own lines edited by his grandson.

"I went back to writing stories. Then I met somebody at a party and he said, 'Why not do a play on W.C.,' so I did that in '76, and that was a success. Then I got sick and was in the hospital without insurance, so my agent said, 'How about another book?' He had the check right there."

This one was a real biography. It took five years and came out as "A Life in Film." The title, says the author, was literally true, because Fields used his own life story for comic situations. It was not a happy life.

"I was in love with a beautiful blond once," W.C. used to say. "She drove me to drink. It's the one thing I'm indebted to her for."

The blond was his wife Hattie, a chorus girl he married in 1900 and made a part of his vaudeville act. When they had a son four years later, Hattie wanted to settle down and live a normal family life. Fields refused, so they split up. She never spoke of him, threw his memorabilia in a closet and raised their son, Ron's father, to reject him.

Fields' comedies, from "The Bank Dick" to "So's Your Old Man," are full of henpecked husbands and outrageously disagreeable wives. The mumbled asides are a legacy from his own mother. Children always side with their mother and usually end up throwing things at their father. There are a lot of sissy sons.

Generally, Ron Fields said, women don't like the Fields comedies. It's understandable. Small children don't usually see much in them either, just as they tend to prefer Harpo Marx before they see the charm of Groucho, another unlovable character.

"W.C. also pokes fun at movie studios," said Ron Fields, "which reflected his own experiences. And he didn't think much of the church: Hattie had become a Catholic somewhere along the line. And there was the boozing. There are a lot of drunks in his movies. My grandfather put away a quart of gin a day, sipping all day long but never seeming drunk. He hated messy drunks."

About 1935 the son, W.C. Jr., who went by the name of Claude, started writing to his father, reaching out. W.C. liked his daughter-in-law and gradually saw more of his family. But Hattie never relented.

"One time she met W.C. by accident -- they lived in Los Angeles, not 10 miles from each other -- when she came to visit my mother, and he stood up and looked at her and said, 'Your skin is still so beautiful.' My mother said it was such a sad moment."

One surprise is the early photos of the comic when he was "the world's greatest juggler" and never said a word in his act. He was handsome and lean. He weighed 135 pounds right up to 1915, when he dropped the juggling and started with the one-liners. He also started drinking.

"He did his first talking film at age 50, which means that most people only saw him as an older man. But he must have been something in the old days. Some of those tricks, like the one with the cigar boxes, jugglers can't figure out to this day."

The cigar box routine is part of tonight's film, along with many classic scenes, including his famous pool cue business.

In that one, Fields is telling a story while he endlessly lines up a pool shot. He talks and fusses and rearranges and aims and talks some more, until the viewer goes bonkers with the suspense. There is something excruciating about it. In another scene, where burglars are singing in the basement (don't expect me to explain) and Fields' wife is demanding that he go investigate, he putters with his socks until you almost can't watch anymore. It is actually painful.

In fact, much of Fields' humor throbs with pain. He regularly is insulted, is knocked about and has things thrown at him. He responds with sullen asides and pompous flummery. Impossible to explain why it is funny, because it really isn't when you think about it.

He buys a hot dog and announces, "I'll pay you at the end of my engagement." The hot dog man says, "Pay me now, you tramp," whereupon Fields puts back the half-eaten hot dog.

"Now, how'm I gonna sell that again?" whines the hot dog man.

Fields draws himself up. "Sir, first you insult me and then you ask my advice on salesmanship. You, sir, are a dunce. D-U-N-C-E," and trails off muttering in that much-imitated nasal sneer, "How do you spell that?"

Why is this hilarious?

Ron Fields is writing a second play about his grandfather, who died in 1946 at 67, and there is a novel in the works and a TV sitcom with characters based vaguely on W.C., his sissified foil Franklin Pangborn and the redoubtable Margaret Dumont of Marx Brothers fame (who also appeared in "Never Give a Sucker an Even Break"). There is also a Fields comic strip, for which the grandson has to dream up six jokes a day.

Fields, 36, has had to cut away the thickets of myth that have grown up around his grandfather. Alva Johnston's biography, for instance, is full of W.C.'s own flamboyant lies, like his running away from home at 9, and the widely read Robert Lewis Taylor version perpetuates the story that he opened dozens of bank accounts around the country under names like Cuthbert J. Twilley and Larson E. Whipsnade.

"He loved funny names. He collected them. But he kept perfectly good records, and his bank accounts are all in his own name. He didn't hate children, either. That thing about kicking Baby Leroy was strictly an act."

Luckily, the facts don't get in the way when you see the man himself, scowling and squinting his tiny eyes when a woman asks him if he likes kids.

"I do if they're properly cooked," he snarls.

Not every subversive carries a gun.