faced with the possibility that Wheaton will be the last stop on the Metrorail Red Line -- wants to build a 900-car garage in the city, and already merchants and residents are settling into camps, preparing to do battle over the site.

"The original plan was to have a large parking facility in Glenmont where there is a lot of land available," said Bill Barron, planning coordinator for Montgomery County. "Now they've moved the end of the line back to Wheaton because of budget limitations, and it's going to be harder to find the room in Wheaton."

The Wheaton Metrorail station, currently under construction, is expected to open in 1989, said a spokesman from Metro. The Glenmont station, the last station on the original plans for the Red Line, is outside of the 81.2-mile limit of rail that President Reagan said the federal government will fund for the District area. Although scheduled to open in the late 1990s, the Glenmont station has yet to be funded, the spokesman said, and Wheaton is now considered, at least for the moment, the last station on the line.

Metro has allocated $10 million to build a 900-car garage in Wheaton to accommodate commuters who will park their cars in the small city and ride the rail system to work.

Barron said a committee composed of county, state and Metro technicians and officials has spent the last six months identifying nine possible sites for the new garage and have narrowed the list down to three.

One site is near Wheaton Forest, a residential community on the east side of Georgia Avenue. Neighbors have organized to fight the garage, but Metro owns the land in question, Barron said.

The second site would be above a group of Metro bus stops -- land that Metro also owns. But Barron said the structure would have to be raised above the buses with six stories of parking garage on top of that. The Wheaton Chamber of Commerce has voiced concerns that such a garage would create too much congestion in that area. Also, the merchants say, the county could use the air rights over the bus stops for a more lucrative building.

The third site would be at the Wheaton Plaza shopping center. Some residents and merchants say they favor this site, but Metro would have to use part of its $10 million budget to pay for the privately owned land. Also, the merchants of the shopping center have yet to express their opinion of the idea.

"Any way you look at this, it's going to be a difficult task," said Barron.

Thomas J. Kim, urban planner for Metro, said the Metro board will make a final decision on the site after public hearings this fall. The board will consider the impact on the neighborhood as well as the cost, he said. The $10 million allocated to fund the garage is expected to cover both land and construction.

But Kim said Metro still considers Wheaton a "temporary terminus" and plans to open the Glenmont station eventually.

"President Reagan won't be around after 1988," he said. "Each president comes in and it's a whole new ballgame."

Although Wheaton may be a temporary terminus, in Metro's book the garage still is needed, said Kim.

"We've found that all down the line people park and ride," he said. "Without a garage, the Wheaton community would find cars on their streets and taking up their store lots."

In addition to the new 900-car garage, Metro also plans to build a four-story garage over a current parking lot that would hold an undetermined number of cars, Barron said.

This garage, which will be under construction soon, is also near Wheaton Forest, a sizable settlement of 30-year-old brick ramblers on the east side of Georgia Avenue.

Two years ago, residents successfully fought Metro's attempts to put the bus stops on land near their property, accepting a "kiss and ride" stop instead. Now residents are battling the possibility of the 900-car garage on the same site.

"We've taken our lumps with one garage, with Metro, with the kiss and ride. . . . It's totally unacceptable to the community to have this garage on this site," said Shirley S. Lynne, president of the Wheaton Forest Civic Association. "The fumes, the traffic, the noise would destroy our community."

Charles Boynton, executive director of the Wheaton/Kensington Chamber of Commerce, said the chamber has not come out for or against any of the proposed sites but has voiced concerns that the plan to put the garage over the bus stop bays would create too much traffic congestion in that area.

A past president of the chamber, Jeffrey W. Harris, said he believes most merchants and at least one committee of Wheaton citizens prefer that the garage be located on an underused parking lot at the Wheaton Plaza shopping center.

Merchants from Wheaton Plaza could not be reached for comment, and planners say the group has not yet voiced its opinion of the proposal. However, other merchants in the city say the Wheaton Plaza merchants have been planning to add several new department stores to their complex and want to use the same parking lot for expansion.

"It will all come out at the public hearings, I'm sure," said Barron. "Any way we go, it's going to be a debate."

Kim said Metro hopes to have the garage under construction by next year and completed by the spring of 1989, in time for the scheduled Wheaton station opening in June 1989.