Historic preservation, once limited to declining but still distinctive inner-city residential neighborhoods, has moved downtown where old office buildings are being renovated.

"There's an appealing ambiance to these buildings," comments Howard Ecker, president of a Chicago-based national office-leasing firm that recently moved to an older building it completely renovated. "It's an alternative to the starkness of the new."

Older office buildings with their smaller floors and elegant details, such as wrought iron railings, marble floors and bay windows, can offer as much warmth and attraction to businessmen as Victorian homes offer to families.

"Oldser buildings have many unique features," says Sam Zell, board chairman of Equity Financial Management Co. which is spending $5 million to restore the 90-year-old Unity Building in Chicago's Loop. "I don't want to be in sealed glass box. Any way, we'd be lost in a big new tower. We can control our environment here. There are smaller floors and more window space. The scale of this building matches our interest."

Equity will occupy 40 percent of the building's 140,000 square feet.

Space in renovated older buildings can even profitably be rented at less cost than space in new buildings, developers have found. Even when a large investment is made, there's a saving in time, as much as 50 percent, which is especially important with today's high money costs.And there can be some occupancy, and thus income, while work is going on.

In San Bernardino, Calif., $1.5 millio;n is being spent to restore the 53-year-old, long-vacant Andreson Building to its former glory as one of that city's important office complexes.

In Denver, the 90-year-old Kittredge Building, with its two-story arched windown, is being restored to its original appearance.

In St. Louis, architect Louis Sullivan's 1981 Wainwright Building, once scheduled to be torn down for a parking lot, has been cleaned and renovated and now houses state offices and courtrooms.

And in Boston, $8 million is being invested in rehabilitating the 55-year-old, flat-iron shaped, Classical Revival-style Appleton Building, including salvaging the bronze door panels, bronze chandeliers, marble walls and sculptured plaster ceiling in the tow-story oval lobby.

"The trend began in the mid-1970s," said Miguel Gomez-Ibanez, vice president of Endevor Inc., a Boston-based architectural and development firm that has been involved in renovating older buildings in New England. "More and more renovation for commercial use has been going on. Previously, most were renovated for residential use.

"All of the buildings we've been involved in were under-used or abandoned, but they all had some degree of historic or architectural interest. We wouldn't do a building if it did not have special architectural character or distinctive styles and workmanship that can't be duplicated," said Gomez-Ibanez.

"Rents in central business districts across the country are so high," points out Ronald m. Puntil, president of Oliver Realty in Pittsburgh, "its's now economically feasible to renovate those old buildings."

Puntil's firm has renovated two vacent commercial buildings in Pittsburgh."Now we're looking for buildings to renovate in other cities, including Philadelphia, where we also have an office," he said.

In Chicago, where the office occupancy rate is nearly 100 percent, a recycling boom has been going on in the Loop, which is the home of a dozen buldings on the National Register of Historic Places. Previously, such buildings were regularly torn down. The early 1970s had even seen the destruction of Louis Sullivan's glamorous Stock Exchange Building, which was replaced by a non-descript tower that promptly went bankrupt.

"If the Stock Exchange Building still existed, it would be a prestige location, commanding top rents, because what you're selling today with a landmark building is status, instant status," maintains Wilbert Hasbrouck, an architect who specializes in renovatoins. Eight of those his firm, Historic Resources Inc., has done are on the National Register.

"People get things in these buildings they would never get in new buildings -- terra cotta ornaments, mahogany trim, brass fixtures, marble entrances," he said.

"yfew relativelly small prestige suites are available in new buildings today, and none with the mystique landmark buildings have. You can get a club room atmosphere that certain professions want. Professional people, such as lawyers, are the primary tenants in these buildings."

Hasbrouck points out that sometimes work begins as simple remodeling, than turns to recycling because of the soundness of the building, and finally ends up as full restoration.

"It's happening all over the country," he points out.

Such buildings are the very same type that owners and developers once fought to tear down. In Chicago, a major battle was waged over the Stock Exchange Buildings. Only the trading room was finally preserved and installed in the city's Art Institute. Today in Chicago a struggle is going on to preserve seven historic hildings, including Zell's Unty Building, in the city's North Loop redevelopment area.

"The city must save the Unity," Zell, appearing before the Chicago Plan Commission, said of the building that once housed the offices of Clarence Darrow and is now on the National Register. "There's a need to save more of these small buildings in the Loop."

Other developers urged the preservtion of additional older buildings, including some the city planning commissioner, Martin R. Murphy Jr., said should be torn down because they are "just in unfortunate locations."

Murphy, a symbol of the barriers to presevation that still exist in Chicago, has repeatedly stalled preservation attempts by the Commission on Chicago Historical and Architectural Landmarks, a municipal agency that has never fought his stonewalling. In the past, developers who wanted to tear down a buildings so they could costruct a new one, or simply put up a parking lot -- Sullivan's Garrick Theatre was torn down for a parking lot -- have gotten the go-ahead from city politicians, no matter what the landmark commission thought.

In this City of the Big Bulldozer, politicians and those with political clout have contrelled what is, or isn't to be preserved. Even today, Hilton Hotels Corp., in addition to tax breaks, has been given a voice in determining which buildings will be preserved or demolished in the seven-block North Loop redevelopment area where it intends to build.

But the economics for leveling and rebuilding is no longer as great, and the growing number of preservation groups -- there are now four local municipal and private preservation groups in Chicago -- are being joined by many developers.