If you want to decorate with a very unusual object these days, you head straight to the site of a fine old building that is being knocked down, or to a wrecking yard or store that deals in architectural elements from such demolished structures.

You spy out the salvaged treasures that are dear to your hearts, then bargain to buy such artifacts of past craftsmanship as carved doors, newel posts, brass door fixtures, chandeliers, classical columns, stained glass windows, gargoyles, ornamental ironwork and Victorian fireplaces.

These and any number of other rescued building components and fanciful fragments of interior and exterior architecture are what Apartment Life magazine describes as "urban archaeology" -- a new art form that has become a fast-developing decorative trend and national collecting movement.

One dealer in New York, Leonard Schechter, even has taken the name Urban Archaeology Limited as the title of his SoHo gallery at 137 Spring Street, where he sells everything from pot-bellied stoves to Corinthian capitals, church altar rails, cast-iron balusters, and other nostalgic pieces of ornament once connected to great buildings of the past. His odd assortment of city relics also has been known to include a single barber's chair, post office boxes and an old-fashioned soda fountain with its original fixtures.

The bits and pieces of cityscapes are hung on walls as art, used as wall brackets to display other objects, and converted into table bases, plant holders, pedestals, bedposts and seating elements. However they are used they add a touch of class and character to modern boxlike rooms that too often are bereft of ornamental or distinction.

One of the older outlets, the United House Wrecking Co. of Stamford, Conn., has been sprawling over six acres and overflowing five buildings for more than a quarter of a century. Ray Bowling, one of the four owners, says the company ceased wrecking buildings about 12 years ago and now deals entirely in what other wreckers wreck.

It is considered the largest such operation in New England, and its gorgeous clutter has been described as "a junk store with both class and personality." Its bargains, sought by children and adults alike, run from 25 cents to $5,000.