The Rockville Board of Appeals gave the go-ahead this week for the Marriott Corp. to build a moderately priced Courtyard motel off Shady Grove Road in Rockville, but a lawyer representing two area competitors says he will appeal the ruling.

Charles S. Rand, representing the Days Inn and the Sheraton Potomac Inn, said he will file an appeal soon in Montgomery County Circuit Court in an attempt to overturn the city's decision.

Marriott cleared its final zoning hurdle Wednesday when the board approved a special exception request that will allow the corporation to build what it hails as the flagship operation for a proposed national motel chain.

The 148-room "Courtyard by Marriott" motel, the first of between six and 10 Courtyard motels planned for the Washington area, is slated for a five-acre tract at Shady Grove Road and Research Boulevard, a prime area targeted for intense commercial development.

Days Inn is on Shady Grove Road near Route 355. The Sheraton Potomac Inn, also off Shady Grove Road, lies between the Days Inn and the proposed Marriott site.

In approving the special exception, the board also voted to grant several variances that the corporation said are needed to accommodate parking spaces at the rear of the motel and a large canopy at the front.

The board's ruling follows the City Council's approval last week of Marriott's request to rezone the parcel from light industrial to industrial park, where motels are permitted as a special exception.

Rand contends that the zoning change, special exception and accompanying variances granted Marriott are so exorbitant that they amount to "creating a new zone" for the property.

"These applications constitute illegal, special-interest spot zoning," said Rand, charging that Marriott was being allowed to change the property's zoning to accommodate its project, rather than change the project for the zone.

Rand also is appealing the city's decision on the grounds that the estimated 250 additional vehicles generated by the development would worsen traffic conditions at four nearby intersections, all of which he described as "failing."

But Joseph A. Lynott, a lawyer representing Marriott, said that the development conforms with the character of much of the surrounding area, which over the past decade has been rezoned from light industrial to industrial park.

Lynott also said Rand failed to consider several area road improvements already under construction, including a southbound ramp from nearby I-270 to Shady Grove Road, and extension of Gude Drive from Piccard Drive to Research Boulevard.

Last June, Marriott announced it was expanding its Courtyard chain after several years of planning and a trial period in Georgia. Besides the Rockville site, the corporation said it has a contract for a site in the Lanham-Landover area and is looking at other locations in the metropolitan area.

The two- to three-story motel would include a restaurant, cocktail lounge, enclosed swimming pool and whirlpool area, a game room and two small meeting rooms. Its main entrance would be on Research Boulevard, with a secondary driveway on Shady Grove Road.

The moderate price category in which Courtyard places itself is the largest segment of the domestic lodging market, Marriott officials said. Rates at Courtyard are between $35 and $55 a night.