A COMBINATION GYM AND BATH, THE LATEST IN HOME AMENITIES - FOR SMALL BATHROOMS

A BATHROOM need not be large to accommodate such bathroom amenities as the whirlpool bath, spa bath, sauna or steam shower. Many models come in standard sizes. The city athlete with limited apartment space does not have to envy the suburban one.

Perhaps the easiest way to transform a standard-size bath or shower in a small bathroom is to install a small steam generator, which simply sends steam into the bath or shower enclosure. Thermasol, in Leonia, N.J., sells a generator for a 3-by-3-foot shower stall for $595. The company also prefabricates a 36-by-60-inch acrylic steam shower bath with sliding glass doors for around $800.

Many companies, such as Jacuzzi, Kohler and American Standard, make whirlpool baths in standard bathtub dimensions, around 32 by 60 inches. Kohler's smallest acrylic whirlpool bath, with four jets, is 32 by 48 inches and costs from $1,475 to $1,650. The company also produces enameled cast-iron whirlpool bathtubs 36 by 60 inches, from $2,900 to $3,500. Kohler even makes relatively compact spas; one is 5 feet square ($1,870 to $2,030). Unlike a whirlpool bath, the water in a spa is treated, kept and recirculated.

One of the more versatile and reasonably priced bath fixtures is Thermasol's Ultima Spa, which combines steam and whirlpool in a single compact acrylic unit. The smallest is 31 by 60 inches and ranges from $3,100 to $6,000. Standard whirlpool baths, when enclosed, can also be equipped with steam generators.

Although most saunas are 5 by 7 feet, they can be custom-made in any size; a sauna for one or two can be worked into a space as small as a closet. The smallest prefabricated units at Baths International in Manhattan are 3 by 4 feet and have a list price of $1,625. Emitting dry rather than wet heat, saunas operate on standard voltage and need independent wiring.

A variety of shower fittings and body spray attachments are available for showers. Baths International sells an apparatus that mixes separate hot and cold water sprays and carries attachments that can create needling and pounding effects; the fittings, however, use up to 15 gallons of water a minute. Complicated shower fittings are best installed when a new shower is being planned. Simple massage fittings cost from $50 to $160; the more complex can cost several thousand dollars installed.

The most elaborate, but still relatively compact, prefabricated bathroom unit is Kohler's Environment Masterbath, which requires an installation space 94 by 106 inches. The digitally controlled acrylic bath includes sun lamps, a misting rain, steam, the capacity to generate warm breezes, whirlpool jets and a regular shower. Its suggested cost is $18,430.

Photo of $1,300 jacuzzi