IN NEW LONDON, Conn., battle lines are being drawn to preserve our roots. The New England Landmarks Trust is going to war against the bulldozers to save a reminder of a happier day.

"We're cautiously optimistic," says Dale Plumner, president of the trust. "Our society is changing so fast that this building is a relic of a different era."

The Building that is rousing emotion is an example of fewer than 50 of its genre left in the United States. Its arches of yellow plastic burst into the suburban sky, its plate glass windows at a rakish angle. The red and white horizontal-striped walls on which the historic brass plaque would be fastened hug the parking lot.

It is one of the original McDonald's stands.

And it is a reminder of a younger and simpler century, when hamburgers cost 15 cents, gas cost 27 cents, presidents held office for two full terms, the number of franchised hamburgers then sold were counted in the millions, not billions, and a '57 Chevy was the ultimate statement of a confident nation. In America, that passes for history, dimly recalled, worth saving.

"It's good to remind ourselves of what we were like 20 years ago," says Plummer.

"As we go into the new decade of less mobility, things that represent a mobile America will become the great old objects," says University of Vermont historian Charles H. Liebs.

"A lot of old architecture of the roadside will be looked at with interest. Not only will it remind people of the golden age of American mobility, but they'll try to harness this image for the future."

Yet the spirit of the '50s is dying. The incriminating evidence that there was once such a decade keeps fading away, erased from the national roadscape like an embarrasing episode banished by amnesia.

Eventually all of the McDonald's "red-and-white," as they're known in the trade, will be replaced, says Stephanie Skurdy, in the Oaks Brook, Ill., headquarters of the McDonald's empire which now spans 27 nations and territories.

"Our operators are business people," says Skurdy. "And they recognize the advantages of remodeling."

This year marks the 25th anniversary of McDonald's. It appears that the corporation is conducting a silver celebration and a funeral at the same time. Maybe we should call it architectural euthenasia, this business of carrying out a mercy-killing on the buildings that gave birth to a national phenomenon.

Some would say they deserve to die. The latest McDonald's incarnation -- introduced in the mid-'60s, made standard system-wide in 1968 -- is easier on the eye.

The modified mansard version, its trademarked roof designed to hide the kitchen air-handling equipment up top, isn't even so "standard" as standard used to be. If the basic mansarded restaurant doesn't seem quite right, there are 12 other flavors available for the facade -- Alpine, Bavarian, Colonial, Country French, English Tudor, French Quarter, Gaslight, Mediterranean, Old English, Spanish, Village Depot and Western.

Beyond that, McDonald's is using old building here and there or employing themes that encourage distinctiveness (and greater sales) in newer ones.

In Lewiston, N.Y., not far from the Niagara River, McDonald's replaced the interior but preserved the exterior of the historic Frontier House.

In Ann Arbor, Mich., a restaurant is decorated with nearly 100 photographs from the city's past -- almost everything, the monthly Ann Arbor Observer noted, except a picture of the historic house that was demolished so that a McDonald's could be built there.

The record isn't perfect. But McDonald's is making attempts to accomodate itself to the character of whatever village, town, borough, city or megalopolis it's operating in.

Still, something eerily momentous is going on at McDonald's, something that looks like the ultimate solution to what the architectural critic Peter Blake once called the "planed deterioration of America's landscape."

In a nation that thrives on nostalgia and hungers for roots, even pop commercial roots, it is desirable to see the historic prime examples of fast-food franchising come tumbling down?

Perhaps we don't need 50 red-and-white and maybe we don't need even 10. Perhaps the McDonald's in New London proposed for the list of the national register of historic places is enough. But in a country that has 5,747 McDonald's restaurants and that gets 300 more each year, the eradication of all the chain's past is inappropriate.

After all, this is the same company whose annual report states proudly: "McDonald's is so much a part of Americana that it is included in a Smithsonian exhibit on 20th-century American life."

Some sort of preservation -- perhaps by adding new space harmoniously to the rear of an existing structure -- "would be the corporately mature thing to do," Prof. Liebs says, "and it could save them money."

At the moment, McDonald's demolition campaign reminds us less of the growth of an industry than of the fact that planned obsolescence has spread from refrigerators and rusty cars to the buildings where millions of mealtimes are passed.