A debate that began in the Prince George's County Council as an obscure discussion about a proposed planning change has escalated in recent weeks, reviving old arguments about development and Metro rapid rail line construction in southern Prince George's County.

At the heart of the matter is the disposition of two dozen acres owned by Willard and Idamae Harris near Southern Avenue and Wheeler Hill Road, north of Forest Heights.

The property, described by council member Sue V. Mills as long-fallow farmland, would have been the site of a Southern Avenue station if a Metro line that continued to Rosecroft Raceway had been built there.

The Rosecroft line is still part of county planning documents -- even though the council and the Metro board opted last year to support a route terminating at Branch Avenue -- because it was incorporated into earlier long-range use plans.

Some council members said the Rosecroft line's presence in the plans ensures that it will be built at some point in the future. The Metro board has never ruled out the possibility of another line serving that part of Prince George's.

Once transportation alignments have been included in such plans, they can be removed only if specific action is taken by the county planning board.

Mills, on behalf of the Harrises, said it is difficult for landowners to find buyers for property that technically is still reserved for a Metro right of way.

"It's prime property," she told her council colleagues last week. "If it weren't for this albatross, they would sell it immediately at a very huge profit."

County planners said this week that the Harrises and others like them are, in theory, able to sell their property but have trouble when potential buyers discover that the county could seize the land in the future if a Rosecroft line is ever built.

Mills' position has been stirring up old conflicts on the council. In the fall of 1983, proponents of the Branch Avenue route won a 5-to-4 victory in the council, but only after years of acrimony.

The debate contributed to the delay on that portion of the Green Line, which will extend from the Anacostia station now under construction in Southeast Washington. Construction is expected to be completed on the Branch Avenue terminus by 1993.

Mills, a supporter of the Branch Avenue route, said there is precedent for removing the phantom of Rosecroft from the county's transit plans.

Metro spokeswoman Beverly Silverberg said this week that the decision on what to do with the Rosecroft plans is "strictly in the hands of the county."

In a preliminary vote on the matter taken last week, council members voted 5 to 4 to ask the county planning board to investigate the possibility of removing the Rosecroft line from the plans, saying that "the economic and political feasibility of constructing the Rosecroft line is certainly questionable."

But the council members who voted against sending the letter described their opposition in larger terms.

"It's very shortsighted for us to take something off that plan when indeed we want to say to the public that this is what we are looking at in the future," said Council Chairman William B. Amonett.

Council member Richard J. Castaldi, who was a Rosecroft supporter and is now a member of the Washington Metropolitan Area Transit Authority board, said that the concern about the future of the Harris farm is a smokescreen.

"I've seen a number of issues like this with people in southern Prince George's County with respect to development and roads," Castaldi said. "All these people don't want traffic congestion, but they want high-quality development."

Council member Floyd Wilson spoke in harsher terms about the motivations of Mills and other south county residents, charging that racism is the real motive.

"Most of these white folks think people coming in here on the subway are going to be black.," he said. "It's a cute little method, a ploy to say that this man's property is at stake." Those who favor the Branch Avenue route "insist that's going to be the only line down there," he said.

"Property owners along the still-proposed Rosecroft line are "not legally burdened but economically burdened" from selling their land, said County Council attorney Robert Payne.

James W. Collins, chief of the county planning division, said that if the council attempted to change the complicated series of plans that govern county land use and policy, they could find themselves "bound and gagged with their own red tape" for up to a year and a half in public hearings and other procedures.