A Muslim congregation of mostly Main Line converts has been dealt a major legal setback in its effort to build a retirement community for aging members in southern Chester County.

A Chester County Court judge has ruled against the Bawa Muhaiyaddeen Fellowship in a long-standing zoning dispute with the East Fallowfield Township Board of Supervisors.

The 350-member congregation wants to build 43 carriage-style houses clustered on a 108-acre parcel that it bought in the 1980s. The rural property is occupied only by a small shrine, or mazar, that holds the remains of the fellowship's late, enigmatic founder.

Originally from Sri Lanka, Bawa Muhaiyaddeen settled in West Philadelphia's University City neighborhood in 1971 and began preaching a mystical form of Islam known as Sufism. He gained hundreds of adherents, many of them white converts to Islam, before his death in 1986.

Over time, the congregation dispersed - mostly to the inner Main Line, but still close to its mosque in the city's Wynnefield section.

The retirement development had been in the works for years and was moving into the final planning stages in 2009 when the township supervisors filed suit to halt the project.

In just the last decade, East Fallowfield's population has mushroomed 44 percent, to 7,400. The addition of high-density housing on downsize lots would, the board has argued, be another assault on the area's treasured rural charm.

Though smart-growth advocates argue that dense development best preserves rural land by keeping as much open space undeveloped as possible, the supervisors don't see things that way.

Several recently built and similar dense-housing developments have "just ruined the footprint" of the township, which features expanses of rolling hills and farmland, recently elected Supervisors Chairman Chris Makely said.

"One of our jobs was . . . to slow down on cluster developments," he said.

The supervisors challenged a crucial variance the township Zoning Hearing Board granted that would have allowed the project to proceed.

The parcel sits in a special development district designed to accommodate construction of the retirement homes. But, according to John E. Good, the fellowship's attorney, a flaw in the ordinance meant the project couldn't meet existing zoning requirements.

The Board of Supervisors and the fellowship tried for two years to reach a compromise.

In his opinion, Judge Ronald C. Nagle said the zoning board had overreached in allowing the fellowship's development to proceed and had ignored important parts of the zoning code.

In the fall, the fellowship had asked the judge to dismiss the supervisors' suit, contending that the board had decided to file it in a closed meeting in violation of the state Sunshine Act.

Nagle ruled that, though the supervisors had violated state law by deciding to file suit in a private meeting, there "was no harm to the public or Bawa."

Describing the members as "obviously disappointed" by the rulings, Good said the fellowship would file an appeal.

Any final decision in the case is a long way off.

Commonwealth Court, which would hear the fellowship's appeal, could take up to a year to rule.