On a Friday afternoon at the Monocle on Capitol Hill, Martin Greenfield, a gray-haired gentleman, digs into his crab cake secure in the knowledge that he is the best-dressed fella in the place.

He is not cocky. This is simply a matter of fact, perhaps even a matter of obligation, because Greenfield is a tailor.

He is not merely an alterations man, a designer, manufacturer or garmento. He is a true tailor, a problem-solver. A diplomat. Confident, forceful, paternal.

"I always suggest the right thing. Sometimes {people} don't listen," Greenfield says. What can he do?

"I can't make you drink the water."

As a young man learning his craft, he'd slip notes into the pockets of suits heading to President Eisenhower. Greenfield's self-named company, a Brooklyn-based concern, produces hand-tailored suits for Brooks Brothers, Donna Karan and others. Presidents Johnson and Ford have worn his handiwork. Today, he is the tailor who knows that retired Gen. Colin Powell prefers to wear a single-breasted suit when giving a speech. It means he doesn't have to deal with complicated buttoning and unbuttoning or fuss with extra fabric. Greenfield knows that President Clinton has a particularly slim neck -- so his jacket collars require special attention -- and that rumors of his chubbiness are greatly exaggerated.

"A lot of people accuse him of being fat," Greenfield says. "He's in very good shape."

The tailor understands that a truly splendid suit begins with fine dry goods, the handiwork of skilled fingers -- not an unsympathetic machine -- and an impeccable fit. By the time it is completed, though, it has become much more than a mere garment.

"A suit is a triumph of civilization," says art historian Anne Hollander, author of "Sex and Suits."

A suit transforms a man into a figure of authority, cloaks him in power and imbues him with an aura of seriousness and respectability. But this only happens when the suit is well-tailored, made of elegant fabric in a somber color.

Men of stature -- or those with lofty aspirations -- do not announce their presence with red jackets, leather pants, sarongs, asymmetrical silhouettes and other foppish ostentation. The man in the gray flannel suit wants to be called "Sir." Not "Stud" -- at least not to his face.

Consider the tailor's attire.

Greenfield's ensemble has a certain amount of dash. It is not your run-of-the-mill navy or glen plaid number, but a midnight blue double-breasted suit with a sky blue windowpane plaid. His shirt is a crisp shade of periwinkle, and heaven forbid that it should have a button-down collar. The tie is a geometric print four-in-hand in which navy dominates. In his breast pocket is a square of navy silk with sky blue polka dots. But the real treasure isn't revealed until long after he has noted the recent revival of flat-front trousers, the draping subtleties between three-on-two and two-on-one button stances, and that ventless jackets are an American invention -- designed to save fabric during World War I -- not a European one.

When he slips off his jacket to settle into the car that will take him to the airport for his flight home to New York, one catches a glimpse of Greenfield's suspenders. The braces, with their glistening gold threads and rose flourishes, are based on a pattern worn by the Duke of Windsor, a sartorial titan. They're a little flashy. But according to the unwritten rules of serious menswear, that's allowed. Suspenders are a man's secret delight. First Client

Greenfield was called to the White House shortly after Clinton arrived in Washington from Arkansas.

"They knew who was who and asked me to come to D.C. so that he could buy some clothes," Greenfield says. He was led up the steps into the president's private quarters. "It's so exciting, to shake the president's hand and to be in his apartment."

No matter that he takes measuring tape, and maybe a straight pin or two, to the inseam of the commander in chief. Greenfield does not flinch. "If it's wrong, I say it. If I need him to dress or undress, I do it. It's my job. Otherwise, why am I there?" He is a straight-shooting adviser.

"I said to him after a while, This is the way you have to dress. If you don't dress the right way, you could ruin my reputation. You're going to be on TV; you see how the shirt is, how the tie is,' " Greenfield says. "Whenever I see him in my suit, it better be right because if it's not right, I get calls."

The tailor launches into a mock telephone exchange with a colleague: "Did {I} make that shoulder? Yes, I put the bumps in it so you could call me.

"{Clinton} is not a clothes horse. These studious people would rather be in jogging clothes," Greenfield continues. "When he first came to Washington, I said, This wardrobe is not going to work.' There were too many leather jackets and not enough suits.

"I try to have everything in dark colors," Greenfield says. "He likes comfort. He prefers single-breasted."

At the first White House state dinner of his administration, Clinton wore white tie by Martin Greenfield for Donna Karan. The Making of a Tailor

It can take up to 100 hours to make a single Greenfield suit. The Golden Fleece label he manufacturers for Brooks Brothers is priced at $900 and up, particularly if the suit is made-to-measure. The top-of-the-line Donna Karan Couture suits, the ones the president wears, start at $1,395. Her made-to-order models, which Greenfield also handles, begin at $1,400.

The tailor has been in business for 50 years. Before Greenfield owned the factory, he worked there. He was still a teenager, a recent immigrant from Czechoslovakia and a Holocaust survivor. Just starting off, he couldn't speak English and he didn't know how to cut a suit. He was a "floor boy," carrying bundles of unfinished garments from one tailor to another. He learned his craft there, eventually bought the factory and works it with his two sons, Jay and Tod. His wife, Arlene, is an artist.

"Everything is made there," Greenfield says, "by United States hands." He's got six "girls," that's what he calls them, who do nothing but make buttonholes. The inner workings of the garments, including the interfacing and the lining, are stitched by hand. "You go buy a $195 piece of garbage," Greenfield begins, and he can't even go on. He sighs. "The cheapest way to get anyplace is through quality. It's true of anything in life."

Don't get Greenfield started on the shame of fused interfacing -- internal support fabric beneath the lining of a jacket that is commonly glued, rather than sewn, in place. Might as well not even call the result a suit. A disgrace, that's what it is. The jacket won't hang right.

"Fused garments only cover the body," Greenfield begins, and one can almost see his facial muscles twitch in disgust. "They can't drape. And to me, that's what gets you to a great suit."

Notice the jacket collar of one of Powell's suits. When he sits down, the blazer doesn't pull away from his neck as if it wanted to stand at attention of its own accord.

Powell's cousin Bruce Llewellyn, noted businessman and owner of the Philadelphia Coca-Cola Bottling Co., introduced Greenfield to the general. Llewellyn arranged the meeting at the Waldorf-Astoria in New York. The Persian Gulf War had just ended, and Powell told Greenfield that when he retired, he'd need "a new uniform."

When Powell finally did shed his Army green regimentals, he turned to Greenfield.

"He looks so good because he loves to dress," his tailor says.

"A general has to dress every day. He's the role model for every soldier. He has to be perfect," Greenfield says.

It would be easy, he says, to start the rumor that Powell is his most discerning customer. But that would not be true. Powell defers to Greenfield's taste. "We've become friends," Greenfield says. "He relies on me."

Powell said through a spokesman, "Martin's an artist, the best in the business."

The major aficionados of bespoke suits in Washington are the lawyers, lobbyists and bankers. They come in and "spend as much on clothes as others spend on a car. They're very finicky."

Washington's political establishment, the folks who haunt Brooks Brothers, for instance, believe in the navy or gray, three-button, single vent, soft-roll suit. (In a soft-roll suit the lapel rolls over the top button.) "It has a small shoulder and is full in the girth area," says a diplomatic Bill Johnson, Brooks Brothers sales representative. In layman's terms, it's a suit that will accommodate a paunch. Johnson pulls out a made-to-measure suit designated for Bob Dole -- a Martin Greenfield Golden Fleece. It's a three-button soft-roll sack suit. "I give him pleated pants; they make him look more stylish," Johnson says.

The color is a risk, though. It's a chocolate brown with flecks of black. Not since Ronald Reagan has brown been a power color.

Today, Clinton does not set the fashion tone for most of Washington's male power brokers. More often, these men are following the precedents set by their fathers and grandfathers. Clinton, explains Johnson, is a bit too edgy for reserved Washington tastes. "He looks good," Johnson says, "but Donna Karan is a little much for them." Her suits typically are made of soft wool crepe with fluid trousers, low gorge (lapel position) and low button stance.

"I get more compliments {on Clinton's attire} from the foreign press because they like the modern look," Greenfield says.

The tailor can't resist a smile. He has been known to wear a $4,000 suit. It was made of a luxurious cashmere fabric and it fit like a dream. Of course Greenfield knows that a man who someday hopes to lead -- a country, not a corporation -- would never spend so much on a suit. Or if he did, he wouldn't admit it. But enough with the jackets that don't button properly, the shabby ties with button-down shirts (those are for sport, understand) the trousers that don't break, the black sneakers being passed off as proper shoes.

"If you're going to represent us," the tailor says, "you should look the part." CAPTION: The impeccably turned out Martin Greenfield on Capitol Hill. A top client is President Clinton (at right in a Greenfield creation at his first state dinner in 1994), to whom the tailor once said, "If you don't dress the right way, you could ruin my reputation." CAPTION: Tailor to the powerful Martin Greenfield has a simple philosophy: "The cheapest way to get anyplace is through quality. It's true of anything in life." CAPTION: Colin Powell was all smiles in a Greenfield creation at President Clinton's summit on volunteering in Philadelphia last month.