IT'S HARD to think of a screenwriter richer than Sterling Silliphant. Even he has trouble. And yet here comes Silliphant - who wrote the screenplays for "The Poseidon Adventure," "The Towering Inferno," "The Enforcer" and many other gargantuan grossers - crawling back to television. Well . . . not exactly crawling. Strutting, parading and crusading.

"To be extremely blunt and to sound totally immodest," says Silliphant in his three-piece suit, "I am probably, in the entire world, among the top five screenwriters in terms of credits, earnings, reputation and inability-to-hire because of constantly being booked. Now that sounds like a terribly immodest thing to say, but I'll just flat out say it, because it's provable."

And yet this rich-rich-rich man who can name his price in price-conscious Moneywood, says he hasn't been all that nourished by the scripts he's written in the past decade and that to find fulfillment he has turned to, of all things, TV. He wrote the 360-page script for, and is coproducing, a 6-hour, $5-million mini-series called "Pearl," to be seen on ABC Nov. 16, 17 and 19. It is the story of everyday lives in Hawaii just before and after the attack on Pearl Harbor by the Japanese in 1941.

Silliphant didn't do this one, he says, for the money. "The amount of money I was paid to write and co-produce 'Pearl' is exactly one-third what I would have been paid to write a feature." He was paid "double" what he got for the screenplay just as an advance on the paperback novelization of it published by Dell.

"It was worth it to me," Silliphant says, "and I made a very considered decision that 1978 would be an income year of less than I'm used to, in order to give me the feeling of writing again. And I will tell you that not only do I not regret the decision, but I feel as though I've just started writing all over again. As if my career is just beginning.

"The films I have been addressing myself to the last four or five years have been so-called event films - all-star casts, disaster-survival, one damn thing after another. It's very difficult in a film like 'Inferno' to do in-depth writing when you've got to have someone say, 'All right now, let's hank that hose up to the 51st floor.' You know, that's what I call 'Let's-go' dialogue, 'Let's-cut-'em-off-at-the-pass' dialogue.

"Well, I find that in television I have been allowed finally with 'Pearl' really to do a piece of character relationship and a development of character, and I'm very happy about it. When you write an 'Event,' it is very difficult to be introspective, to take time. The kinds of things we used to do in the so-called golden age of television when literally three people sat around a table and opened their souls up - you just can't do that in the movies today because unless you're Woody Allen, no one will come to see it.

"For the rest of us, we have to play the game and for that we are highly compensated, and I think fairly well respected in our community. But we're not necessarily gratified as authors. It sounds like a dull, dumb stupid complaint because it's certainly not new. It goes all the way back to the Dashiell Hammetts and the William Faulkners and F. Scott Fitzgerald. Everybody came out there and said, 'Christ! I couldn't write!' But I'm not saying that. You can write. But I don't think you can write for films today the way you can write for television."

Silliphant is not talking about writing for series television but instead "the most exciting new development for a writer that I have experienced in the past decade" the vaunted mini-series - "a noble piece of nomenclature I detest" - that makes more than one night to unravel. Silliphant, however, has had plenty of experience with series television. He created and wrote 70 scripts for "Route 68," a cult item on CBS from 1960 to '64, and also wrote most of the superior ABC cop show "Naked City," which, like "66," was ambitiously shot on location in real places. After that, Silliphant just did "isolated things" for TV and it was natural to assume he'd gotten fed up and decided to go for the big money of big movies.

"I didn't leave television in anger," he says. "I didn't leave in frustration. Actually I left because I kind of wasn't wanted; I wasn't 'not wanted,' but I wasn't wanted enough that anything I ever wanted to do got made."

Now, however, his enthusiasm over "Pearl" has "kicked me into a whole television thing." He is busy converting Ayn Rand's 1,280-page whale "Atlas Shrugged" into eight hours of television for NBC. Then he enters a "three-year exclusive deal with ABC" which may include a series based on "Pearl" if it clicks on the air. It is unlikely, incidentally, that it will bomb.

Silliphant certainly radiates success. He does not seem beset with self-doubt. "I'm a very professional, disciplined writer. I go to the typewriter. I don't have a block. If I don't write well, I just keep hacking away and maybe a line or something finally comes out and at least the eight hours will have been well-spent. Or it may not have been. But I never say, 'I can't write today so I'll go out and goof off.'"

He is at the top of his craft in good, solid commercial screenwriting. Though he insists on writing novels, the most literary thing about him is perhaps the way he peppers his clippity-clip, Tom Snyderesque monologues with the word "literally." Thus: "I have friends who are top screenwriters who literally have not been able to get a film made in three or four years." Or: "More and more I find our society homogenized in the sense that the same attitudes, literally, prevail much more than they used to."

Silliphant has lived for literally 2 1/2 years in chic and preposterously prosperous Mill Valley, near San Francisco - "It's so good that we moved out of L.A." - with his part-Vietnamese wife, Tiana. The fact that she is part-Asian was one of the things that made Silliphant interested in the Pearl Harbor story.

"I was very concerned with what it was like to be a first-generation Japanese in Pearl on Dec. 7, 1941. Your parents were born in Japan, yet you were as American in your concepts as any Caucasian. And now your homeland bombs your new homeland, so what sort of dilemma does that pose for you? Well, the Japanese in fact overreacted against their Japaneseness. Committees were formed; the use of chopsticks was banned, which shows you the extent of ridiculousness and war reaction. You can't believe what went on."

Silliphant himself was "19 going on 20" when the bombs fell, and the next year was in the Navy. When he wrote "Pearl" he had to return to the Navy, and go to Army authorities as well, for military cooperation in the production of the film. This also meant getting military approval of the script, but only a few items became matters of debate.

For instance, the Navy didn't like the fact that an officer's wife went into a bar and ordered a double Scotch, so Silliphant obligingly changed it to a Scotch and soda. "You understand the subtlety of the difference, right?" Then there was the fact that "almost all the civilian casualties in Honolulu that day were caused by our own anti-aircraft shells falling to the ground. The Navy didn't really like that. They said there was no point to bringing that up again. So I omitted the word 'naval,' and we just say, 'anti-aircraft fire.' That took care of the Navy."

The Army had one complaint, a scene in which Angie Dickinson, as a colonel's wife, "does one of those 'Tea and Sympathy' numbers" with her husband's young jeep driver in the back room of a brothel, something Silliphant acknowledges would have been "immensely immoral in 1941 - strictly 'Scarlet Letter' time" even if it had not taken place in a brothel. That particular location, however, was what irked the Army, so the affair was transplanted to the sugar cane fields.

Of the finished "Pearl," Silliphant says without a hesitation," I'm really pleased. I hate to say that, but I have been so displeased with my own work for the last 10 years that to see something that you really like is refreshing." He considers his script; "It's not bad. It really isn't." He considers the show; "It's big and lush, very entertaining, suspenseful, character-development, prime-time, high-class soap opera.And on its deeper level, I think it says a lot more."

Such hyperbolic self-appraisals might be suspect if Silliphant weren't also tough on his real or imagined flops. "I saw 'The Swarm' in a theater and I almost died," he says, though that buzz-bomb's major failing, he acknowledges, was probably not his screenplay but the simple fact that "a bee is not that frightening. Anything you can just . . ." Wham! He slaps the desk ". . . and say, 'Goddamn it, get outta here,' is not going to terrify people. When I have to sum up the trouble with that film, I just say, 'A bee ain't a shark.'"

And though "Route 66" was surely one of the best-written television shows of its day, maybe any day, Silliphant can recall sa bummer of two. "One of the worst ones was with Joan Crawford. She was very nice, she admired the show and so she called us, but when you put one of those old Hollywood stars against what we were trying to do, it just doesn't work. It was called 'Same Picture, Different Frame,' and it was just awful. I am so ashamed of it!"

He half sighs. "In the normal course of keeping up an inventory, you're going to do some awful work."

"Pearl," however, finds him back in fighting form, and he would be the last to apologize for his own table-thumping bravado. "It's important that a writer have this ego. If you don't, you're in trouble as a writer. I've got my teeth sharpened," he says, sounding like he means it. "I feel like a killer now."

And a shark ain't a bee.