The National Trust for Historic Preservation, the country's largest private preservation group, is turning its attention to real estate development under the direction of its new president, Michael Ainslie.

Because preservationists now realize that "the way to fuel the engine of preservation is to get into the business," he said, the trust has begun investing in real estate and managing it, as well as working with community groups that do the same thing.

The trust's new National Main Street Center, for instance, is providing technical assistance for downtown economic development in cities with populations of 50,000 and under -- "within the context of historic preservation."

Ainslie, who took over the 150,000-member organization in July is no stranger to such work. A graduate of the Harvard Business School, he was president of Palmas del Mar, a subsidiary of Sea Pines, Inc., and developed a 2,700-acre residential and resort community in Puerto Rico. He also served as a deputy director of New York's Model Cities programs in the late 1960s.

Before joining the trust, Ainslie was chief operating officer for a nitrogen products manufacturer in Cincinnati. He restored his own 1880s' Queen Anne home in Cincinnati, along with a number of other properties. He also organized a neighborhood business corporation to revitalize the East End of that city.

He believes that the trust and the historic preservation movement have become much more than ad hoc groups working to save old buildings for the purpose of turning them into museums. He predicts that a range of preservation and cultural organizations will become full-fledged developers.

One example, he said, is Station Square in Pittsburgh, an abandoned railroad station that the Pittsburgh History and Landmarks Foundation is turning into a major commercial-retail complex. Private funds and Urban Development Action Grant money from the Department of Housing and Urban Development are being used.

An advisory committee of developers, lenders, architects, builders and insurance executives interested in the reuse of historic properties is also being planned by the trust. The group will look into the problems of financing redevelopment projects, deal with local opposition and propose alternatives to local zoning and building code requirements.

With help from the committee, Ainslie believes the trust can find ways to effect change in cities across the country.

"The toughest problem conservation has to face is the future of downtown commercial structures," he said.

That issue is one he is facing as chairman of a new urban task force made up of representatives from HUD, the National Conference of State Historic Preservation Officers, the Interior Department, the National League of Cities and the U.S. Conference of Mayors. It was recently organized by the Advisory Council on Historic Preservation, a federal agency that oversees federal involvement in protection of historic properties.

In some cities, such as Charleston, S.C.; Pittsfield, Mass., and Louisville, preservationists, mayors and developers have been at odds over the use of action grants, which are often used to create downtown malls at the expense of historic properties. Some action grants are being used specifically for historic preservation, however.

"Preservation is not against new construction," Ainslie said. "It is for compatible new development that respects economically viable older buildings."

Ainslie sees the need for new zoning ordinances that allow for the transfer of development rights from historic properties to other building parcels. This would help eliminate the economic deficit that current zoning ordinances create, he maintains.

The second major issue facing preservation as a movement is neighborhood conservation, Ainslie believes. Preservationists in several cities are working to insure that housing restoration does not mean the displacement of low-income residents.

Ainslie wants to develop a model program of neighborhood conservation that will help those families hold onto their homes, and contends that a totally free market will not work. It has to be structured to provide other alternatives, he contends.

He is an advocate of do-it-yourself development and believes that renters should buy their buildings before prices get out of control. One new trust program, the first in a series, will train neighborhood leaders in this area. It is funded by HUD's Office of Neighborhoods, Voluntary Action and Consumer Programs.

Citizen control and involvement in real estate development is a central issue for Ainslie.

Asked how he would like to be remembered as president of the trust, he said: "As having made preservation a term that is synonymous with the citizens of America regaining and reasserting their right to control the design and shape of their cities. . . ."