A narrow, wooded ribbon of land stretches between the Bethesda and Silver Spring areas, a portion of a rail spur that once was used to haul coal to Georgetown. Trains stopped running there more than a year ago, homeowners now walk their dogs along the deserted tracks, and gardens are planted nearby.

"Remember the jungle scenes in 'The Bridge on the River Kwai'? It looks just like that. It's idyllic," said James F. Chatfield, a Chevy Chase homeowner whose yard abuts the railroad line. "We walk these tracks and we get a great deal of peace out of that."

Today, the unused rail branch, owned by CSX Corp., has become a battleground between county officials and neighborhood activists.

Montgomery officials have proposed taking over a section of the old railroad line between Bethesda and Silver Spring to build a mass transit route for buses, trolleys or rail cars. The plan has set off protests from homeowners, such as Chatfield.

The widening controversy is viewed by federal and local officials as a classic test of competing demands for transportation and tranquility in a thickly populated area.

The tangled issues have led to multimillion-dollar negotiations, environmental studies, engineering calculations, public hearings and political debates involving federal, Montgomery County and District of Columbia officials. The dispute eventually may result in a court contest, officials say.

From the county's vantage point, the proposed transit route would provide sorely needed public transportation to connect two booming business districts, Bethesda and Silver Spring. It would link the Metro subway system's Bethesda and Silver Spring stations, which are on separate branches of the Red Line, and would help relieve mounting traffic congestion on key roads such as East-West Highway.

A county study has concluded that it "is both desirable and feasible" to build an East-West Transitway, as the proposed mass transit route has been labeled. "This critical resource must be pursued now, not later," according to the study. The plan has won allies among Bethesda and Silver Spring chambers of commerce and some commuters.

But homeowners, including prominent residents such as former senator and secretary of state Edmund S. Muskie, have denounced the proposal. Many residents have contended that a transit route overlooking their back yards would constitute an invasion of privacy. It would result in noise, pollution, safety problems, losses of trees, reduced property values, faster development and more traffic, they argue.

"It would be rapid transit running within 40 or 50 feet of our home," said Anthony F. Czajkowski, a retired Central Intelligence Agency official and history professor whose East Bethesda yard adjoins the tracks. "We'd be in economic limbo. The whole area would deteriorate and depreciate."

The rail spur once was used mainly to transport coal to a General Services Administration heating plant in Georgetown. With coal increasingly delivered by truck, the company halted rail service on the line in March 1985 and later sought federal approval to sell the route.

Even when the rail spur was in use, it caused little complaint among residents because trains made only about six or eight trips a week.

"It was looked on sort of fondly. It ran, at most, twice a day," said Reeve Vanneman, a leader of the Greater Bethesda-Chevy Chase Coalition, a group formed to fight the transitway proposal. "Whatever you run up and down there every three minutes is going to be a nuisance."

A controversy initially arose last year over a section of the rail branch along the C&O Canal in the District. Historic preservation organizations and neighborhood groups in the Palisades area objected to proposed development of the land, which overlooks the historic canal and the Potomac River.

In an attempt to preserve the scenic city area for hiking, bicycling and recreation, the National Park Service began negotiations with CSX Corp. to acquire the rail tract in the District. Park Service and CSX officials say they expect a deal eventually to be struck. The land's value is now being appraised.

Amid the debate, the Interstate Commerce Commission, a federal agency that must weigh the CSX proposal to abandon the rail branch, announced plans for a far-reaching environmental study of the issue. The agency's move to draw up an environmental impact statement is expected to delay any action in the District or Montgomery until next year.

In April, the Montgomery County government opened its campaign for a mass transit route. Officials said the proposed transitway could be completed as early as 1990, attract up to 11,700 riders a day and save commuters nine to 15 minutes each way between Silver Spring and Bethesda.

The transit route was described as a way to bridge one of the most severe gaps in the Washington area's transportation network -- a shortage of cross-county routes connecting suburban centers. In the past, most major highways and mass transit lines were designed to link the suburbs with the downtown area.

The proposed transit route would be used not only by Montgomery residents. According to the county's preliminary study, nearly 40 percent of the riders would be Prince George's County and District commuters, many working in the Bethesda and Silver Spring areas.

That study, drawn up partly by the Metropolitan Washington Council of Governments and the Richard H. Pratt consulting firm, recommended up to eight express and local stops along the 4.4-mile transitway, including Connecticut Avenue and East-West Highway.

Under the preliminary proposals, rush-hour service would be provided at least every six minutes and possibly as often as every two or three minutes. The project would cost from $22 million to $43 million, the study said. In addition, CSX Corp. has estimated the value of its county land at $6.9 million.

A key issue is whether to operate buses, trolleys or some other form of mass transit vehicles. Proposals for diesel-fueled buses have caused concern because of prospects of noise and fumes. County officials are weighing other options, such as electric-powered buses or light rail, a modern trolley system.

The proposed transitway -- the latest of several plans devised for revamping the old railroad spur since the late 1960s -- has drawn at least tentative support from county and regional agencies, including the Tranportation Planning Board, a coordinating panel affiliated with the Council of Governments.

Montgomery County Council President William E. Hanna Jr. termed the transitway a "real possibility," arguing that improved cross-county transportation is needed. "Nobody is going to go for putting diesel buses in there," he said, but he added, "there is interest in the possibility of a trolley line."

The county Planning Board has adopted a proposal to clear the way for the transit route, but the panel also called for measures to protect adjoining communities from noise, pollution and excessive development. The board's plan would rule out diesel buses unless special devices are installed to curb noise.

Some residents favor the plan. Fred Fravel, a transportation consultant who lives near Silver Spring, said he will stop driving to his Bethesda office and use the transitway if it is built. Today, bus service is too slow, he said, and East-West Highway has become "a continuous parking lot."

But many homeowners whose yards overlook the old railroad branch say that the route should be preserved as a park or hiking trail.

"We'd lose trees. We'd gain a lot of noise and pollution. We don't want it," said David W. Stewart, a transitway opponent who lives in a Chevy Chase town house near the route.

Hiking, bicycling, railroading and other groups have pressed for preservation measures. One coalition proposed establishing a "capital crescent" hiking trail, stretching from Georgetown to Silver Spring. Other groups urged that old-fashioned trains be operated on the spur as a "rolling museum."

Some Montgomery County residents who live along sections of the rail branch between Bethesda and the District also have expressed alarm. Although county officials have suggested using this stretch temporarily as a park trail, they have raised the prospect that the mass transit route might someday be extended to the District.

"What they really want is to grab all of it and decide later what to do with it," said former senator Muskie, who has a town house overlooking the tracks. "It's the uncertainties that surround their options that have got us all aroused."