Maryland highway officials say that a 6-by-12-foot sign that urges motorists stuck in traffic in the Shady Grove area of Montgomery County to complain to local officials may violate a law designed to protect roadside beauty.

The sign, which asks in 9-inch-high letters, "TIRED OF THIS TRAFFIC?," is visible to the thousands of commuters who jam Rte. 28 each morning as they try to get to I-270 and points south.

It urges motorists to protest a planned annexation to Gaithersburg that would allow construction of 600 to 700 new homes on the 148-acre Washingtonian Country Club. The sign also gives telephone numbers for Montgomery County Council President David Scull and William Hanna, chairman of the council's Planning, Housing and Economic Development Committee, and for Gaithersburg Mayor Bruce A. Goldensohn.

A member of the Westleigh Citizens Association, one of the neighborhood organizations that sponsored the sign, said Lyn Coleman, of the county planning board and the Maryland-National Capital Park and Planning Commission, called her Monday (two days after a story about the sign appeared in The Washington Post) and told her that "we needed to take the sign down. She said she was trying to do us a favor. She said she had gotten a call from the beautification department of the State Highway Administration and they were going to issue a citation. She said she didn't want to see us get a citation."

Coleman said yesterday that state highway officials told her they had received anonymous calls complaining about the sign and asked her to find out who owned the land on which the sign was placed.

"The only reason I called her the Westleigh resident was to be a mediator," Coleman said. "I wanted to let them know so they could resolve it before it got to the point where somebody got a citation."

Carrol T. Richardson, chief administrator for the State Highway Administration's beautification section, said yesterday, "It seems this sign would be illegal." He said the only roadside signs allowed on private property are those advertising a business on the premises.

Elizabeth Beall Banks, a farmer in her 60s, on whose pasture the sign stands, said she has had more than her share of run-ins over the years with land dealers, planners, and highway officals, and has no intention of taking the sign down.

"I'm waiting for them to call me," she said. "I've got a speech ready they'll hear across the Atlantic Ocean. In fact, I hope they will call. I'm just waiting."

Harvey Perry, president of the Westleigh Citizens Association, said the protesters don't seek to stop development or scare off potential home buyers.

"The intent," Perry said, "was to make people aware and get people to alert their public officials that they're getting tired of this traffic."

Since the sign went up two weeks ago, county officials said they have received a flow of calls and postcards asking when they intend to widen the road, and how they will handle the annexation.

"I tell 'em that we'll listen to what everybody has to say, which is exactly what I do," Hanna said.

County planners said they expect to expand Rte. 28 by 1985 or 1986. Mayor Goldensohn said the developer of the golf course tract, Jay Alfandre, has agreed to consider signing an annexation agreement that would allow homes to be sold only as road construction is completed