CONTEMPORARY bakery products have conquered the aging process. Their newly-acquired immortality reflects the substitution of carefully selected and tested oils, gums and stabilizers for old-fashioned milk, butter and eggs. In the past, bakers were obligated to baby their products, baking small quantities from fear that some might stale before purchase.The new substitutes eliminate such managerial headaches. More expensive bakeries may add butter, use superior toppings and glazes, but the same principles apply: underneath silky swiss chocolate glazes, often lie mix cakes, hydrogenated vegetable oil "buttercreams" and jams made of algal gums. Size, color and moistness are goals often more prominent than flavor.

Using good ingredients requires commitment to an ideal that is not necessarily important to the customer. It requires, besides expense and inconvenience, skill in the use of ingredients that require more care.

Take for example, butter. It is not easy to handle during the summer because it softens and melts. Croissant and danish doughs must be thoroughly refrigerated before rolling butter into them. All surfaces and utensils should be cool. Cookies made with butter turn rancid if stored more than a week at room temperature. Unlike shortenings, butter does not contain antioxidants (BHA and BHT) to slow down the onset of rancidity.

Shortenings, on the other hand, do not require so much care. Danish and croissant doughs made with them do not need refrigeration, and are insensitive to the vagaries of weather.Even on hot days, no special care need be taken to make good shortening doughs.

Jorn Nielson of the Danish Baker in Potomac, Md., says, "I don't use butter anymore. In the beginning, when I first arrived here, I used it. But it gets soft so fast, making it difficult to work with in a bakery. It has a low melting point and the danish dough doesn't flake well during baking. After baking, the pastries made with butter don't stay crisp.

"I only use butter in some cookies and special things for Christmas. In butter pastries, as soon as they cool, they lose their butter flavor and all you are left with is a higher price."

He said that very few of his customers have ever complained about the missing butter. According to him, they are more aware of the flakiness and moistness imparted by vegetable shortenings.

Not all bakeries have made a total transition to vegetable shortening. Many of the oldest and most reputable establishments retain some products made with butter; others use various proportions of butter and shortenings.

Watergate Pastry, for example, makes its pie dough (for its wholesale pie business) with 50 percent more butter. Any more and the dough would melt and stick to the pie press, a machine that stamps balls of pie dough into aluminum pie plates. The press saves a tremendous amount of labor for pies which, to be competitive, must remain cheap.

The second most important ingredient in pastries and cakes is pastry cream, also know as custard. No American bakery can live without it. It is found in eclairs, napoleons, Italian cakes and filled donuts. When made with milk, egg yolks, cornstarch, sugar and flavored with vanilla, it leaves an impression of coolness and digestibility.

But pastry cream, because of its richness, is also prone to spoilage. In summer months it spoils, even if refrigerated, within four days. Pastries and cakes filled with it should be sold on the same day.

"In the beginning, I made real custard," said Nielson. "But when summer arrived and, you know how summer is in America, it spoiled too fast. So, after a few months, I started using a mix, just like most bakers. It's not a bad product if you stir a little margarine into it for flavor. It never spoils. I can fill my danish with it and sell them at room temperature. You could never do that with real pastry cream; the health department would make you refrigerate the pastries. Who wants to buy an ice-cold danish?"

Artificial pastry cream keeps very well. It looks and feels like the real thing, but its taste leaves much to be desired. It is made of sugar and cornstarch, like real pastry cream, but has no eggs or milk. Instead, artificial pastry cream contains yellow food coloring to imitate the pigments of eggs, titanium dioxide to make the pastry cream opaque and vanillin to substitute for vanilla extract.

Because it is immune to spoilage, artificial pastry cream can be prepared days in advance and left at room temperature. The pastries and cakes filled with it can then be sold until they become too soggy to handle. Because it contains no eggs or milk, pastry cream can be frozen in large batches, thawed at will and used to fill pastries and cakes. They can then be refrozen, ready for sale. Under such treatment, real pastry cream would turn into scrambled eggs.

Before 1950, virtually all Washington area bakeries used whipped cream on their cakes and filled pastries, but it lasted at most three days before it either dried up, soured or turned rancid. It varied on color, as it still does, depending on the cow's diet. In the summer, it turned faintly yellow from the vitamin A absorbed from eating fresh hay.

When MOJ, one of the first artificial toppings, was introduced by wholesalers, few bakeries were interested. But those that did start using it found they could keep the topping indefinitely, even at room temperature. In addition, it was pure white. Customers were more attracted to the consistently white topping than to the seasonally yellow or ivory-colored whipped cream.

The "cream" of 95 percent of filled pastries and cakes today is whiter, firmer, more easily spread, less temperature-sensitive and 75 percent cheaper than its mentor, whipping cream. The component fats -- hydrogenated coconut, palm and soybean oils (oils do not melt at room temperature) -- and the resulting foam -- stabilized with vegetable gums -- melt neither in hand nor mouth.

The public seems to have tired of whipped toppings, though. Nelson sells many chocolate-dipped cream puff pretzels filled with raspberry and vanilla creams. He tried switching to topping, but his business fell off immediately. cSo, instead of continuing to use it, he bought a freezer to store real whipped cream pretzels without losing any to spoilage. "That freezer has paid for itself many times," he said.

Many years ago, before cornstarch became prevalent, bakery apple pies were made "homestyle". That is, they were made with freshly peeled apples, sugar, spices and a pinch of flour. Bakeries employed children, usually the offspring of the baker and his wife, to peel green apples. Unlike today's watery red delicious, winesaps or staymans, those apples exuded little juice and the pie filling lost little volume.

In the 1950s, Clear-Jel, a modified cornstarch which, on cooking, produced its namesake and stayed that way even after freezing, became part of bakers' repertoires. Now, thanks to its thickening powers, bakers can buy frozen or canned fruit, thicken the juice (which they usually dilute) and pack the pies with more cornstarch glue than fruit. Those pies that aren't baked off can be frozen and kept in reserve. Even they retain more original fruit flavor, though, than canned pie fillings, which are preserved with sodium benzoate, prepared months, even years in advance of use.

What is the future of bakeries? More and more, a dearth of skilled help steers contemporary bakeries toward the ultimate temptation -- bake-offs. No, they are not parties, nor are they regional baking contests. They are breads and pastries frozen and oven-ready. They take little skill to thaw, proof and bake.

There are countertrends, however, Maurice Bonte, of Bonte Patisserie at 1316 3rd ave., New York City, is one of the remaining bakers in the United States who uses only the best -- milk, butter and eggs."It's very possible to own and run a bakery which uses only good ingredients," he explains; "You just charge, accordingly." That, of course, is easier in a city the size of New York, and when the owner is the baker and therefore interested in more than enlarging the business. One of the country's most celebrated pastry chefs, Bonte is willing to make less money on each item he sells, to work harder to make the same amount of money that someone else would make, in his case 12 hours a day, six days a week.

"People come here from all over because they know they will get their money's worth," he said. "But I don't charge that much more, especially considering the cost of ingredients and labor. In fact, my customers know they are getting bargains considering the care, ingredients and appearance we put into our products."

Bonte charges $9 for a six-inch cake which would sell for $6 at a bakery using shortenings and cake mixes. He believes that, for a third more cost, the customer has a cake that is not only twice as good but truly something special.

Bonte has never seen any overwhelming advantages to using "shortcut ingredients." Because the richest of all pastries are never more than one-third fat, using shortening, to him, would be false economy. "Why should I go to the work of producing a beautiful pastry or cake which, when eaten, leaves a film in my mouth?" he said. He considers the raw ingredients available in America just as good as those in France, where he trained, but French laws help to maintain the quality level of bakeries there. Explained Bonte: "By law, bakeries that are marked tout au beurre (all butter) can't even grease their pans with shortening." Bonte has tried commercial glaze, one called apricoating, but thought it was like bubble gum. As for shortening versus butter, he considers it easily identifiable in bakery products. "When it starts to stick in your mouth, that's when you know it has shortening in it."

French bakers in America have been surprised to find that customers expect their pastries to be large, like the all-American prime rib.

Christian Domergue, owner of the Bread Oven at 1220 19th St. NW, doesn't understand why Americans want such large pastries. He feels that for America to have better pastries, people will have to start choosing quality over quantity.

"Compare our eclairs to those of Heidi's bakery. Ours are very small -- almost like fingers -- but they are made with good custard. They cost $1.35 each. Heidi's are three times as big but only cost 90 cents., They look and taste awful, but sell well. The customer thinks, 'Oh my goodness -- look what I can get for 90 cents!'" he said.

Giant Food's Heidi bakery is proud of its eclairs; in fact, Arthur Becker, the bakery's supervisor, says, "We base our reputation on our eclairs. We make the shells at the central bakery, and they are sent to the store bakeries, where they are filled." According to Giant Foods spokesman Barry Scher, Heidi's eclair shells are bake-offs, their custard a vanilla vegetable-base powder, which Scher describes as the same filling other bakeries use. As for Domergue's opinion of Heidi's eclairs, Becker added, "It's a matter of opinion whether he liked it or not; I happen to like them." "

In the meantime, America's bakeries continue to serve diverse tastes. Heidi bakery survives, and so does Bonte.