Edward F. Carl, a retired Navy commander and a banker, has lived in his comfortable three-bedroom McLean rambler since 1962, aware, but unperturbed, that one day a new highway would stretch just beyond his backyard.

So he was especially incensed -- "quite disgusted," according to his wife, Evelyn -- when last Friday's mail brought a letter from Shannon & Luchs, the major Washington-area realty firm, boldly urging him to sell now and get out.

"Now may be the time for you to consider re-locating," warned the letter, signed by two agents of the firm's McLeans office. It cited current federal government plans to proceed with a highway that would connect the Dulles Access Road and Interstate Rte. 66.

Carl was sufficiently put out to contact his Fairfax County supervisor, John P. Shacochis (R-Dranesville), who yesterday won approval from the county board for a resolution asking officials of the Narthern Virginia Board of Realtors to investigate what Shacochis called "scare tactics" by Shannon and Luchs.

"Trash like this" said Shacochis, "is absolutely to be condemned." The realty firm's objective, the supervisor added, was merely to encourage resales in order to drum up business.

That contention was strongly denied yesterday by an officer of Shannon & Luchs' McLean office.

"I'm not blockbusting. I'm not creating scare tactics. This was being done in the area of public service," said office manager Robert Pannier. "What is wrong with drumming up business? If the supervisors are going on record as being against drumming up business, then I want to know where they stand on business."

Pannier declined to say how many letters were sent out.

The letter to the Carls, dated Feb. 28 and signed by agents Harry Padbury and Dorothy Koehler, suggested that because their quarter-acre lot "could be adversely affected" by the proposed highway construction, they should consider selling now, before ground-breaking begins.

"Experience has shown that once actual construction begins in an area it is more difficult to market property," the letter said.

The proposed 3.5-mile extension of the airport road through a predominantly residential section of McLean and Falls Church is scheaduled for groundbreaking sometime next year, an FAA official said yesterday.

Joe Hayden, an official of the 8,200-member board of realtors, said yesterday that Shannon & Luchs' approach appeared to violate the spirit of the trade group's ethics code. He said the matter would be forwarded to the organization's grievance committee.

Wann E. Gays, chairman of the grievance panel, said, "This is the first time I've ever heard of anything like this."

Meanwhile, several other residents of the McLean suburb where part of the proposed highway extension eventually will lie, expressed unhappiness over receiving the same notice.

"We didn't appreciate that letter," said Margaret Hrnung, who lives in a two-story split level up the street from the Carls. "we aren't stupid. We're not too happy about the road, but that (letter) only makes us feel more uneasy. They tell us to sell because (our house) isn't worth anything, but when they sell it to somebody else, it is going to be the best thing on the market."