Hardy Amies, dressmaker to the queen and a London menswear designer of taste and influence, was in Washington recently for dinner at the British Embassy. We caught up with him as he was setting off on a leisurely walk to inspect shop windows in Georgetown and on Connecticut Avenue. These are his observations on the state of menswear:

* "The suit has gone through many changes, attacked by all kinds of casual clothes. But the jacket, shirt and tie remain triumphant. They're practical. The jacket, with a minimum of four pockets, is a man's pocketbook. Nothing is more becoming to a man than a good collar and tie."

* "What looks awful is a jacket without a tie--worn with an open shirt. If it is so hot, then wear a shirt without a jacket."

* "Never [wear] short-sleeve shirts." It is not so bad if you have beautiful arms, but Amies says a man's elbow (or a woman's) is not an erogenous zone.

"The best jacket is the easy-fitting blazer, even as part of a suit. For a while the French got hold of it and made it too tight. It should have military brass buttons. The best cloth is still gray flannel."

* "The shape of jackets in the 1970s was tight and fitted at the waist. The 1980s shape is loose and casual."

* "Suits should not be in colors, but the new shirts in colors, particularly mauve, give a fresh interest to suits. Picture this: a gray banker's suit, mauve button-down shirt and mauve foulard tie. It is ideal for a gray-haired man who plays on his club's tennis team--or wants to look that way."

Amies barely pauses. "My hardest job is to show men how to dress well when casual," he continues. "American men competing for the Lily Pulitzer prize with all those terrible bright colors and things . . .

"My idea of summer casual wear is white flannels trousers and a white silk shirt, open at the neck, sleeves rolled up just below the elbow." Some of his other observations on casual wear:

* "No man ever owns too many sweaters. But never wear a sweater with a suit for business."

* "Sweaters look best with crew necks. There is nothing dowdier than a V-neck long-sleeve sweater. A sleeveless V-neck sweater can be good with a common tie and sport jacket."

* "The best blazers are double-breasted. If a double-breasted jacket is low slung with buttons placed low , every man can wear it. If he has a [large] stomach, it helps him disguise it."

"New double-breasted jackets can easily be worn open. No vents on the double-breasted blazers, please. Center vents are desirable on single-breasted jackets. You can't wear a single vent in a double breasted suit--it is ungrammatical."

Amies gives some ways of dressing up and dressing down:

* "The biggest favor a woman can do for a man is to burn his frilly tuxedo shirt."

"The best tuxedo today is a midnight-blue blazer suit without brass buttons, a pleated white voile shirt and narrow, but not too narrow, maybe inch-wide black satin tie with long ends. No cummerbund. Patent leather moccasins. No jewelry. No fancy cuff links. No studs. What is stunning [with a tuxedo] is a silk shirt, a plain silk shirt, slightly off white."

Amies concludes with some general principles:

* "Ties must be narrow enough to look modern, wide enough to honor the silk."

* "The shoe of the epoch is the moccasin with a sturdy sole. My tassel moccasins from Lobb the shoemaker to the queen , which cost $600, are 10 years old. They will go to the grave with me."

* "Shoes should be brown or black. With a gray suit, shoes can be brown if you want to dress [the suit] down, or black."

"Never white leather shoes. Never any time for anything. You can wear white canvas shoes. With a white suit, do not wear white shoes."

* "Co-respondents' shoes--the kind the guilty party wears in a divorce case, two-tone brogues with white filled in on top--are okay. Saddle shoes are not."

* "Khaki canvas shoes are great for summer with white suits."

* "Khaki cotton pants and a blazer are perfect for the office. The best thing [in summer] is a white voile shirt."

* "The button-down shirt is the phenomenon of the 1980s. In the era of long hair and waisted fitted suits, you had long, pointed shirt collars. When they decided to shorten the points on the shirt, they found they stuck out. That's when they decided to button them down. Button downs are now a hit with the Europeans who find the American sporting look very agreeable."

* "Jeans that are clean and well-pressed and worn with well-polished brown moccasins, a blue button down, club tie and a good blazer--you can go to Buckingham Palace and they would . . . think you looked quite nice and would let you in."

So what was Hardy Amies wearing as he toured Washington on an 85-degree day?

A single-breasted seersucker jacket ("It's as international as jeans"), khaki chinos, button-down blue voile shirt and a yellow foulard silk English tie.

As he would say, very acceptable.