Almost everyone involved agrees that a proposed motel and conference center along Rte. 7 in Loudoun County would A be an economic boon to the county. It would generate more than $200,000 a year in new tax money for the county and provide about 100 new jobs, according to an attorney for the developer.

But the proposal has brought heated opposition from residents, county planners and historic preservationists, who contend the complex is not in keeping with long-range county plans and would bring commercial development to a carefully preserved rural section of Rte. 7.

Tonight the Loudoun County Board of Supervisors is to hold a public hearing on the issue, beginning at 7 in the county office building in Leesburg.

The proposal by developer Daniel M. Ross calls for a four-story Sheraton motel-conference center and restaurant on Rte. 7, across from the Xerox Corp. training center and adjacent to the historic Belmont Plantation, which is owned by IBM. If approved, construction of the $20 million complex would be completed in about two years, according to a spokesman for the developer.

Opponents of the plan say the complex would be built too close to both Rte. 7 and Belmont Plantation. They add that there are numerous other sites near Leesburg and Dulles International Airport that are more suitable to such a project.

"None of us has any objections to a Sheraton motel. Everybody in Loudoun would be glad to see it," said B. Powell Harrison, president of the Piedmont Environmental Council and a leading opponent of the Sheraton project. "But put it where it will do some good, not where it will do incalculable damage to Belmont, to Rte. 7 and to the historic preservation effort in Loudoun."

The major issue is "compatibility," says John Dugan, director of planning, zoning and community development for Loudoun County.

"We want something much better than along I-270 (in Montgomery County) and certainly nothing like Rte. 1 (in Alexandria and Fairfax County)," said Dugan, who with his staff has recommended against the complex because "it is not in accord with the comprehensive plan" for Rte. 7.

The comprehensive plan, which guides future growth for the area, permits industrial park development, provided such development be in an attractive, campus-like setting that complements neighboring properties. However, the more detailed sectional plan for the area surrounding the motel site has yet to be completed, and county planners have urged that no rezonings be approved until the plan is set.

Currently, the eight-acre motel site is zoned residential. Developer Ross, who owns Sheraton motels in Reston, Arlington and Silver Spring, has asked that zoning for the site be changed to industrial park because "most of the land around it is zoned industrial park," according to Ross' attorney, Richard R.G. Hobson.

Last year, a divided county planning commission rejected the proposal, saying it was not in keeping with the county's comprehensive plan. This summer, however, the commission approved rezoning for the complex, provided Ross builds the entrance and exit on Ashburn Road (Rte. 641) instead of Rte. 7. Hobson said that plan is unacceptable to his client.

Since the complex was first proposed last year, Ross has made several changes in the plan, including setting the complex back 300 feet from Rte. 7, instead of 100 as originally proposed, building it taller, and increasing the number of rooms from 165 to 240.

Opponents to the motel project concede that the other two major firms in the area, IBM and Xerox, both have industrial park zoning, but they contend both have stayed within county guidelines to preserve the rural flavor of the area.

IBM owns the Belmont Plantation house, about 350 yards from the motel site, and several thousand acres surrounding the home. The house, built between 1799 and 1802 by Ludwell Lee, one of the founding fathers of Leesburg and an aide de camp to Lafayette, is on the National Register of Historic Places. Although the land is zoned for an industrial park, an IBM spokesman said last week the company has no immediate plans for the property. When IBM bought the property 12 years ago, it agreed to preserve Belmont and 54 acres between the house and Rte. 7, a commitment IBM plans to honor, according to the company spokesman.

The other major piece of property near the motel site is the Xerox Corp. training center, a mammoth conference center that trains employes from major corporations throughout the country. The center, also zoned industrial park, is more than half a mile from Rte. 7 and cannot be seen from the highway. County planners say that helps preserve the rural atmosphere of the area.

If the motel complex were approved, it would be the first highly visible and "the first commercial development allowed along this stretch of Rte. 7 since 1944" when Loudoun officials established a policy of no commercial development in the 14-mile stretch between Sterling and Leesburg, according to preservationist Harrison. "There's one Exxon station, but that was built in 1938, before zoning, and it was grandfathered in."

The Xerox center is not considered a commercial development in zoning parlance because it does not do business with the public, although the center attracts 12,000 to 15,000 conferees a year, according to a company spokesman, in addition to the 300 Xerox workers permanently employed there.

Attorney Hobson concedes the motel would be the first development of its kind along this stretch of Rte. 7, but counters opponents' arguments that there are numerous other sites near Leesburg and Dulles Airport just as well suited to the project.

"Ross looked at other places before he chose this," Hobson said. "He considered Leesburg but he feels it's too far from Dulles. "We think the Sheraton will induce development. That's a plus."

The former chairman of the county's Industrial Development Advisory Committee, William Malone, says his group favors the motel because "I don't think you can avoid development along Rte. 7. It's best to channel what growth you can. . . . We'd like Sheraton in the county and you have to go where Sheraton wants to go."

Preservationists consider any talk of development to be a minus.

"It's in the wrong place . . .," argues Constance Chamberlin, executive director of the Waterford Foundation, one of the county's oldest historic preservation organizations, founded to protect the village of Waterford. " Approving this project would set a precedent of disregard for the protection of historic sites."