This is no mere stove -- it's a handsome, high-priced `cooker'. At $5,000 and up, Britain's AGA is definitely for the serious chef

We're not sure how much time Princess Diana spends slaving over a hot stove. But if her Prince is terribly particular about his Bubble and Squeak, or wants his Toad in the Hole cooked ``just so,'' at least they have the ``proper'' cooker. It's called an AGA -- for Amalgamated Gas Accumulation. And other members of the rich-and-famous persuasion have warmed up to this British-made cooking unit.

Billy Joel heats up leftover Campbell's chicken noodle soup for his ``Uptown Girl'' on an AGA. One was installed in the Frank Lloyd Wright house Falling Water more than 40 years ago. Paul McCartney, John Updike, and Ben Kingsley also have them. Never to be one-upped, Martha Stewart, gourmet cook, stylist, and caterer, has two.

Something else the above-mentioned share. Money.

The AGA is priced in the United States from $5,000 for a two-oven model to $6,000 for the four-oven model, which has separate ovens for roasting, simmering, baking, and warming. Add about $500 for installation, plus any state and local taxes.

If you haven't seen an AGA, or even heard about one outside the leather bindings of a British novel, it's not surprising. Although they have been manufactured in the little town of Coalbrookdale in England for more than 60 years, they were commercially introduced to the US just last July. Since then, 25 to 30 have been sold in the US. Between 3,000 and 4,000 are sold in Britain each year. (A British cookbook on the AGA is the only one available now, but an American one is being worked on.)

The AGA was invented in 1922 by Dr. Gustaf Dalen, a Swedish physicist and Nobel laureate. Confined to his home after a laboratory explosion left him blind, Dr. Dalen became concerned about the time his wife spent in the kitchen preparing and monitoring everything she cooked. His solution: one cooker capable of every cooking technique. Hence the AGA.

So why would you trash your Amana electric range for a $6,000 AGA cooker? You probably shouldn't unless you are very serious about food and are willing to alter your style of cooking.

The most intimidating thing about this cooker -- notice we never refer to the AGA as a common ``stove'' -- is its simplicity. There is one control: an on/off switch. And it's always ``on.'' (You may want to turn it off if you vacation for a few weeks, but it takes 24 hours to get everything back to correct temperature.) There is nothing else. That means no temperature gauges, knobs, dials, or heat thermostats. You cook by ``mode'' rather than temperature.

There are two cooking surfaces on top -- one set for boiling, the other for simmering. When not in use, they are kept covered with heavy, chrome-topped insulating lids to help conserve fuel. Most cooking is done in an oven rather than on top -- again to conserve fuel.

A beef stock, for instance, is brought quickly to the boil on top of the cooker, then placed in an oven to simmer for hours. Bacon is ``fried'' in an oven. Items such as pancakes and toast are cooked directly on the surface plates.

Onions may be ``fried'' while brownies are baked at the same time in the same oven.There are no cooking odors or transfer of flavors because of constant ventilation through a central flue.

This can work adversely. If you can't smell what's cooking, you can easily forget it.

Judith Asphar, who performed with bravado at a recent AGA demonstration and has cooked for the Rockefellers and fed the Kissingers, made a confession between courses. She once prepared an elegant carbonnades de boeuf and put it in the oven to slow cook, then forgot it. Voila! Carbon de boeuf in just three days! Fortunately, the AGA is also self-cleaning.

The AGA is always ready. No preheating, and no ``cold'' or ``hot'' spots. No blasts of hot air.

This means even roasting and baking. The weighty ovens hold moisture as well, so no need to baste the turkey. And best of all, Ms. Asphar sniffed, ``your food is not nuked.''

The AGA is always very warm to the touch, and therefore may not be practical in warm climates without proper ventilation. According to distributors, it gives off heat comparable to 10 100-watt bulbs.

The cooking process is that of heat stored at a constantly ready-to-use temperature and held in a heavily insulated cast-iron unit. The AGA is a serious instrument and is not to be taken lightly in any respect. It tips the scales at about three-quarters of a ton, or roughly as much as 352 toaster ovens.

About the only thing it doesn't do is flash broil, as there is no exposed flame. For that you'll need a salamander. And if you're serious enough about cooking to get an AGA, you know when I say salamander, I'm not talking about a lizard.

Efficiency aside, from a purely aesthetic point of view, the AGA is stunning. The three coats of hand-applied enamel glow brilliantly in seven available colors, and the polished chrome lid-caps gleam like convex mirrors. There is nothing flimsy, shoddy, or mass produced about it.

If you order now, you will most likely be the first on your block to have one, unless you live just off Rodeo Drive.