YOU'RE ALL wet if you think the current preoccupation with supersized bathtubs has anything to do with cleanliness being next to godliness. The pleasures of today's bathroom are sensual - which, you understand, doesn't necessarily mean a Roman orgy everytime you take a bath.

Soaking in a hot bath is one of life's two or three greatest pleasures. The dream-like state it induces helps you float away to other places, other times: to ancient Rome, where the citizen was plied with pleasure in the city baths; to Turkey, and a houri pouring rare prefumes upon the fortunate recipient; to Japan, where the family enjoys its ritual ablutions. The water buoys up the body and the psyche. It stimulates the nerve ends, and relaxation is not only possible but inevitable.

Washington has yet to succumb to the California preoccupation with bathing that has spawned - Wet - The Magazine of Gourmet Bathing. But Washington does have Superman-and Wonder Woman-sized bathtubs. Some come big enough (though again, not necessarily) for parties, some with elaborate water massage jets, most with gold-or silver-plated and sometimes jeweled hardware and all with acres of mirrors.

All the big local plumbing supply companies are plugging the spa bathtub, especially Thomas Somerville Co. (Jacuzzi and Kohler) and the Atlantic Plumbing Supply Co. (Kohler). Other wholesalers can supply other makes, some quite exotic.

The ultimate is most likely the Environment by Kohler - a sit-in saunalike cabinet that in a 29-minute cycle can bring you Baja Sun for a tan, following by Tropic Rain, Jungle Steam, Spring Showets and, to dry off, Chinook Winds. It costs about $12,000, but only a plumber looking at your house pipes could tell you what the installation price would be.

Among its luxuries, the Environment includes four heat lamps, four sun lamps, six 24-carat gold electroplated sprayheads, steam generator, two warm air circulating systems, a hand-held shower, stereo speaker, porthole cabinet and a potthole window (install your own aquarium to view). Options include a stereo radio with eight-track player, a painting silk-screened on the translucent back panel and a comfort pad with pillow. Kohler, somewhat defensively, asserts that a 50-minute cycle would cost less than 20 cents in water and electricity. A cheaper version, called the Habitat, has just been introduced at $6,000, not counting installation.

Jacuzzi makes a number of whirlpool baths for both swimming pool and bathroom installation. Largest bathroom tubs are the 5-and 6-foot Roman Baths, including three whirlpool inlets - basic prices are $1,100 and $1,250. In color, you have to add about $200, but then you can choose from 12 colors with names like Valentine Red and Sunburst Yellow. Gold-plated fixtures cost from $110 to $405 more.

Architecturally, the most beautiful of tubs is the round red (black, beige, green, blue, yellow or white) one designed by Fabio Lenci and manufactured in Italy by Teuco for the Hastings il bagmo collection (carried locally by Somerville). The tub alone is $2,000. For $4,400 you can have a cylindrical see-through shower cabin atop the circular tub. In the backwall of the shower are accessory compartments, a full-length mirror, hand spray, thermostatic mixer controls and coiled chrome tower holders and warmer that are really the hot water pipes in disguise. A see-through sliding panel keeps the towels dry. On yes, there's also a contoured seat.

Probably the funniest is the Baja Luv Tub, a heart-shaped whirlpool bath available for $800 (not counting the cost of the plumber) from Somerville.

Two versions of the wine vat tub, practically a standard fixture on California decks, are now being made by Jacuzzi. The Sequoia Whirlpool Spa (6 feet wide, 4 feet deep) is a redwood tank with an electric heater that costs $2,260. The Paragon (8 feet square, 3 feet deep) fiberglass tank version with an electric heater is $3,890. California Cooperage produces just one of the many versions that can be ordered in kit form from California.

A lot cheaper is the remodeled scalding tub, originally used to skin pigs, installed in a deck of a house built by architect Fred Andreae and his wife, Christine, in Overall, Va.

"The gutter from the roof feeds the tub with rain water," Christine Andreae says. "The tub is sunken into the side of the deck. We have a hot water line outside that can warm it up. A plug at the bottom of the tub can be pulled to drain it. The redwood lid lies flush with the decking. The tub is 3 feet deep and 4 1/2 feet in diameter. It fits assorted numbers of children or two friendly adults."

Andreae prefers the outside shower, a small balcony hanging on the outside of the house. "The delight is in the experience of a hot shower in the tree tops with flowers blooming on the ledges and nice smelly soap."

Janice and Ted Sherman, who have a new house in Virginia, built in a tub (about 6-by-6) of an exotic brown manmade marble. The tub was ordered from a company in California by their builder, Steven Zimpel, who put extra reinforcing in the floor to keep it from crashing through. "It took an extra hot water heater," said Janice Sherman, "so I could fill it up."

Ted Sherman, according to his wife, "is a shower man. His shower has all those special shower heads built in. He tried out my tub twice - when he had a bad back. He had it put in for me. When the world is too bad, I escape to the bath with a book. I recently read a good bit of 'Coma' in the tub."

The three Sherman boys have suggested that the tub is a good place to wash the two golden retriever dogs. But so far, their mother has been vigilant. The workmen who installed the tub thought Mrs. Sherman could use a buoy or a life-preserver.

The bathroom is very fancily done with a lattice wallpaper on the wall, a lavatory/dressing table of matching faux marble and brown wall-to-wall carpeting, which also covers a step. Penne Poole, the decorator who did the interior of the house, likes to fill the platform above the tub with green plants.

Just before the house was finished, the Shermans realized that they would have to go out into the hall, past an open staircase, to get to the bath from their luxurous bedroom (with fireplace, deck, dressing room, study and laundry room adjacent). But Zimpel saved the day by adding a linen closet/passageway and a sort of landing above the tub. It works almost like a secret passage.

One of the older bathrooms in town - so old no one quite remembers who put in the wall-to-wall mirrors - is the one in the Georgetown house still called after Ulysses Grant and now owned by real estate investor Connie Russell. The blue mirrors cover almost everthing, including the mirrored dressing table and a mirrored fireplace surround. During Russell's current redecoration by Sarah Jenkins of W&J Sloane, an art deco wallpaper appropriate to the room has been installed.

Architect Elliott Gitlin has designed several fanciful bathrooms. In one he did for Dr. and Mrs. Alfred Kapin the tub was placed for a view of the garden. The house has since been sold to the Iranian embassy.

One of the great bathtubs of the area is in McLean in the home of Virginia and John Forstmann. The house was designed by Tom Wright of Brown and Wright Architects some four owners ago, and recently added to and remodeled by the Forstmanns, who have lived there seven years.

The tub is sunk into the floor, adjacent to a sliding glass wall leading to an enclosed garden. Steps lead down to the tub. Originally there was a glass enclosure to protect the room from the shower, but the Forstmanns removed the showerwalls and covered the whole room with a blue and white octagonal Italian tile.

"I love it," says Virginia Forstmann. "And my friends when they see it say, 'Why, Virginia, that's a whole side of you we didn't know.'"

She says that sometimes her husband has joined her in the tub. But most of the time he has his own shower in his own bath around the corner. The children, Kurt, 10, and Marina, 9, love the tub, especially when it is filled up with liquid soap to make bubbles.

Suzanne Shaw, a decorator who has done a number of opulent houses, has just finished a bathroom with rosewood (in some places formica) paneling and black granite counters and ledges. The tub is half sunk in the center of the room. The faucets are tigers' eyes, semi-precious stone. The washbasin is gold-colored. The toilet and bidet are black. The ceiling is black mirror set with down lights.

Two of the biggest local bathtubs are in the VIP suite and the ambassador's private quarters of the new Japanese embassy residence. The Japanese, as everybody knows, enjoy communal bathing, wooden hot tubs and looftah washers. The tubs the embassy residence, like the building itself, are immense - about 6 feet square in white porcelain with fancy golden fixtures. The tubs required two faucets to get enough water to fill them.

In Jack Seward's book "The Japanese," published by William Murrow, he writes:

"The Japanese custom of the bath has deservedly been called the Grand Passion of the people who embrace it because they are addicted to cleanliness and because it is as relaxing as two or three martinis at the end of the day. If you are invited to dinner in a Japanese home, and your host urges you to bathe shortly after arrival, you need not take umbrage at what you might construe as a totally unnecessary comment on the state of your hygiene. He will be only following the dictates of his code and suggesting that you indulge in what to him is a most pleasant and relaxing pre-dinner custom.

"In the winter a long, hot bath keeps the Japanese warm in their chilly house long after the event, and in the summer, the air of the evening feels somehow less hot and oppressive after a long soak in 105-110-degree water . . .

"The tubs in private Japanese homes are usually made of cypress. They have covers to keep in the heat. It takes about 30 minutes to heat the water. Perhaps the widest area of disagreement about Japanese and American bathing practices is, indeed whether or not men and women, otherwise stranger to each other, should bathe together. Given their naturalistic acceptance of nudity (again in its proper place), the Japanese custom of konyoku or mixed bathing should not be at all surprising . . ."

Stewart also writes about the Japanese inns with their natural hot spring baths, and the Apollo Bath in the town of Arita where 10 tubs are in "a glassed-in cable car which moves horizontally along the coastline some 50 yards up in the air. Passenger-bathers undress outside the cable car, then get aboard and ensconce themselves in cozy tubs in preparation for a leisurely round trip above breath-halting scenery." CAPTION: Picture 1, Getting clean is only half the fun. Marina and Kurt Forstmann, enjoy their family's sunken tub surrounded by blue and white tile.; Picture 2, The Environment is the ultimate in body care and costs a cool $12,000; Picture 3, Harvey Baskin's black bath. Photos by Harry Naltchayan and Charles Del Vecchio - The Washington Post; Picture 4, When the Shermans built their house Janice Sherman chose a 6-by-6 foot brown man-made marble tub for the master bath and surrounded it with lattice wallpaper., Photo by Charles Del Vecchio - The Washington Post