"I don't think many people appreciate how sweet and witty he is," says Joyce Williams, speaking of her brother-in-law Tennessee.

"I'm not sweet!" Williams shouts.

"He's a prince and a gentleman," says Edmund J. Perrett II, a young friend who was the first -- and apparently last -- person to abbreviate Williams' name to the final "essee" (pronounced E.C.). "I don't know why Essee gets such a bad press," he says.

"I'm an irascible, bad-tempered old man." Williams explains.

Bearded and rather dignified-looking at 68, Tennessee Williams, Pulitzer-prize-winning author of such plays as "A Streetcar Named Desire," "Cat on a Hot Tin Root" and "The Night of the Iguana," is a having lunch at the Watergate before heading to a White House reception for the five recipients of this year's Kennedy Center Honors.

When he heard he had been selected, "I couldn't believe it," he says. "I thought I was too controversial."

With him, besides his sister-in-law and Perrett, are his younger brother Dakin, an Illinois lawyer who is running in the Democratic primary for the seat being vacated by Adlai Stevenson III, and Lady Maria St. Just, an old friend who is his escort for this festive day.

The brothers Williams are flip sides of 20th-century American man: the Bohemian scamp who declared his homosexuality on nationwide TV by telling David Frost, "I cover the waterfront," and the clean-cut, back-slapping regular Joe who is putting himself before the voters.

Dakin Williams suggests a question for Tennessee: "Who's your favorite brother?"

"I've only got one," says the playwright, and a wave of raucous laughter engulfs the party.

"Tell him about the Shakespeare connection in the family," says Dakin.

"Oh, stop that!" Williams complains. "There's no such thing, and they've never heard of Shakespeare in Washington."

Unperturbed, Dakin explains that the family is "descended from the dark lady of the sonnets. A. L. Rouse has verified it."

"That's absolute bull---!" says Williams.

In both brothers' calendars, March 1980 has special importance. Tennessee's new play, "Clothes for a Summer Hotel" (about Zelda and Scott Fitzgerald), will open in New York (it opens here in January), and Illinois Democrats will nominate a Senate candidate.

Dakin Williams has endorsed President Carter for reelection. His brother has done the same -- just now, in between bites of trout. "I'm supporting Carter," he says, "although I love Mrs. Kennedy -- Rose -- and Pat Lawford. I wish she were running. It's time we had a woman president."

The president may be disheartened to learn, however that Tennessee Williams' political activities have been rather limited through the years. "I've only voted once in my life," he says. "That was when I came of age."

Williams looks well, but he is having no compliments today -- about his health or anything else. "Who's well at 68 and a half?" he asks rhetorically. hThen he grins, tugs at his beard and takes darting looks into the distance, as if trying to summon a nonexistent waiter, while spitting out misanthropic observations on whatever subject is brought up.

Artists: "Most artists are terribly selfish." He recalls William Faulkner's utter refusal to join him in conversation when the two men met, first in Hollywood, later in Paris. And Edna Ferber's remark, when Williams was introduced: "The best I can manage is a mild 'Yippee.'" Some artists are "bitches," he says, "You know, like so many homosexuals are bitches."

The 1970s: "I don't understand the '70s. Everything is so dead now. The young people don't seem to care about anything. We used to care deeply about things. Now they just want to go to discos."

His most acclaimed plays: "People loved 'The Glass Menagerie. It still makes more money than any other play of mine. I don't know why. I get so tired of seeing it."

Even yesterday's honor: "The only real award a writer can have is a good morning's work. And usually he can tell if it's a good morning's work. I can't fool myself anymore."

His life, as he has recorded it in his autobiography, "Memoirs," and in assorted interviews and essays, has been crammed full of bad fortune, from an ugly family situation that led to his sister's receiving one of the first lobotomies, to last year, the murder of his gardener.

On Key West, where Williams has been assaulted, burglarized and taunted by hooligans, things are quieter now. "All's quiet on the southernmost front," he says, adding that his friend Dotson Rader exaggerated a lot of the trouble anyway.

But Tennessee Williams puts up little resistance when asked whether all the adversities and unpleasantnesses have hopelessly soured his outlook. Is "muddling through" the highest achievement of the characters in his plays? "I'm trying to think of anybody I've encountered in my long life who's done anything more than muddle through," he says. "I can't think of anybody."

"I can't think of anybody either," says his sister-in-law.

For all Williams' disclosures about his sex life, he says it was "very uninteresting except for the 14 years I lived with one person [artist Frank Merlo]."

"I gave up sex six months ago," he adds, "and it was no good even then."

But no amount of despair will keep him from writing plays, or from rising as early as he can get some sustenance -- 5 a.m. at home, about 7:30 in hotels -- and sitting down at his typewriter.

His interest in Scott Fitzgerald dates way back, he says. "I always sensed what he was like . . . He was a man who didn't spare himself at all." And he describes Zelda, who will be played by Geraldine Page, as "a lovely figure."

Williams was up late Saturday night, but up early yesterday morning to get in a few hours of writing. To his consternation, his manager had failed to provided him with a typewriter, and the hotel had failed to provide his room with stationery. There wasn't even a Gideon Bible in the room.

On the other hand, Williams was stunned to find the phone number for Walter Reed Army Medical Center on his desk, which he took -- unkindly -- to have been a special precaution on his behalf.The hotel insisted it was in all the rooms, "but I was here last year and they didn't have it," said Williams skeptically.