A Montgomery County citizens' group this week condemned a county proposal for a light-rail system linking Bethesda and Silver Spring, saying the plans are based on "unrealistic" estimates of cost and revenue from riders.

The cross-county system would share a now-unused railroad right-of-way owned by CSX Corp. with recreational trails, according to county officials.

In the latest chapter of the two-year dispute over the 11-mile right-of-way between Georgetown and Silver Spring, the Greater Bethesda-Chevy Chase Coalition, a 500-member organization, said a study it commissioned showed that the rail system would cost more than $100 million, not $61 million as the county estimates.

The study, made by the management and technology consulting firm of Booz, Allen & Hamilton Inc., also said the county's estimate of the number of people who would use the rail system is 47 percent higher than the average ridership of similar rail systems in other areas.

County officials were surprised by the citizens' study, according to Glenn S. Orlin, chief of planning and programming in the county planning office. Orlin said he had not had a chance to examine the report and could not comment on it.

Another county official, George Mosburger, chief of property acquisition, said this week the county appears to be near an agreement to purchase the property from CSX.

Trains using the line, known as the Georgetown branch, carried coal to a General Services Administration heating plant in Georgetown until CSX halted operations two years ago. Coal is now delivered by truck to the plant, which heats 120 federal buildings. CSX has asked the Interstate Commerce Commission, which regulates railroads, for permission to abandon the right-of-way because it no longer makes money.

Staff work on CSX's abandonment petition has been completed and is being reviewed, according to an ICC spokesman. He said he could not predict when the commission would make a final decision.

Other sources said the decision had been expected before now, but has been delayed. One said ICC attorneys are taking extra time to study the record of the abandonment proceedings because they believe a D.C. citizens' group may file a lawsuit challenging the ICC's eventual decision. The president of the Palisades Citizens Association, George Pugh, said his group is "poised to go to court" if the ICC decision in any way "would encourage development" on the right-of-way land in the city.

Disputes among citizens' organizations, several federal agencies, the Montgomery County government and the railroad have marked the more than two years since CSX told the ICC it wanted to get rid of the right-of-way. Residents near the right-of-way and the National Park Service are concerned that CSX, which has said it expects to get a high price for the property, may sell it to developers who would build houses or commercial buildings on the land.

The park service and CSX are negotiating a proposed swap of the portion of the right-of-way that passes through the C&O Canal National Historic Park for land the park service owns elsewhere. The park service is working on appraisals of the right-of-way property and of the land that would be exchanged for it.

National Park Service Director William Penn Mott Jr. wants all of the property converted to public recreational use under the provisions of the National Trails Systems Act. Mott recently asked the ICC to "issue an order ... requiring the railroad to offer the right-of-way for sale for public use 'on reasonable terms,' " and said the commission should determine how "reasonable terms" are reached. If the right-of-way is turned into trails, it, along with the C&O Canal Towpath, would "create a 20-mile inside-the-Beltway loop" nearly free of vehicular traffic, Mott said. A portion of the railroad property in the District runs through the C&O Canal National Historic Park.

The National Trails Systems Act establishes procedures for converting unused railroad rights-of-way into recreational trails. The law provides that when an agency or trail-user group agrees to take financial, legal and managerial responsibility for the right-of-way, the ICC must not permit "abandonment or discontinuance inconsistent or disruptive of such use." A user group could operate the property for recreational purposes until the railroad company wants to resume train service on it. Thus far, no company has decided to resume rail operations as authorized by the act.

The Montgomery County government wants to purchase the county's portion of the right-of-way under terms of the trails act to assure that it gets all of the property, Mosburger said.

Although CSX owns most of the land, some portions belong to individual owners and would revert to those owners if the rail line is abandoned.

It is unclear whether Montgomery County, if it purchased the property from CSX, would still be bound by the trails act and required to turn it over to a user group that qualified under the provisions of the law, according to an attorney familiar with the law who requested anonymity.