Dulles air traffic controller David Leffas had landed planes hundreds of times before; he just never had been in the pilot's seat.

For 20 years, Leffas had been present in the six-seater airplanes he had been guiding to the ground only as a voice booming over the cabin radio. Now, 10,000 feet above the ground, he was taking orders from a fellow air traffic controller and trying to distinguish the planes from the buildings, knowing how obvious the differences were on the controller's radar screen down below.

"Landing from the air was definitely seeing the situation from a different perspective," Leffas said.

Leffas, who instructs new controllers at the Dulles tower when he is not working the controls himself, was the first air traffic controller to participate in the Aircraft Owners and Pilots Association's "Fly a Controller" program, begun in January.

With the endorsement of the Federal Aviation Administration, the program already has helped several hundred controllers and pilots better understand each other's job.

"The more a controller knows about what a pilot does and vice versa, the more awareness, understanding and respect each one has for the other's craft," said Leffas, one of the program's biggest advocates.

"The intent all along has been communications. We AOPA traditionally work closely with the FAA, and we traditionally have our disagreements with them. This program is something both of us can do to enhance the safety of the airspace system," said Patricia E. Weil, director of the communications division at AOPA.

According to Weil, hundreds of air traffic controllers across the country already have participated in the program and flown alongside a pilot in the small general-aviation aircraft that they have helped to land via a radar screen for years. For many of the controllers, it was the first flight that they had ever taken in a small aircraft, Weil said.

AOPA has compiled a brochure about the program that provides the participants with the "dos" and "don'ts" of the controller-pilot flights. The brochure includes such commands as "do give the controller a thorough briefing about the content and conduct of the flight," and "don't continue to fly if the controller becomes ill or uncomfortable."

The AOPA suggests that once the plane has landed, the pilot and controller should sit down in a more relaxed environment and discuss what each has learned from the flight. Leffas, for example, learned that some of the newer pilots were afraid of the faceless "voice over the radio," and also that the voice was too loud and at times very hard to understand because of the din from the plane engine. PROFESSIONAL

Daniel S. Buser Jr., public relations director at the American Bankers Association for the past eight years, has left the nonprofit sector for a job with Doremus & Co. in Washington. He will serve as vice president and general manager of the company's Washington office, which specializes in public and government relations for financial and trade organizations. Buser received the Public Relations Society of America's Silver Anvil Award twice for excellence in public relations during his time with ABA. He also has served a term as secretary of Commerce for the Commonwealth of Pennsylvania and has been a press secretary for two governors and a U.S. senator. A spokesman for the ABA said it has not yet filled Buser's job and has no plans to do so in the near future.

The Private Carrier Conference, a trade association made up of manufacturers, distributers, shippers and receivers who also operate their own truck fleets, has promoted Thomas L. Moore to the position of managing director. Moore joined the conference two years ago as the editor of the group's publication, The Private Carrier. TRADE

After serving as executive director of the Federal Bar Association for the past 18 years, J. Thomas Rouland has joined the Restaurant Association of Metropolitan Washington as executive vice president. Rouland succeeds John S. Cockrell, who started with the restaurant group in 1945 and has served as chief executive officer since 1959. At the Federal Bar Association, John Blanche, a retired Army colonel who has been deputy executive director there for the past three years, will take over as executive staff director.

At its annual meeting in New York recently, board members of the Chlorine Institute selected a local association executive as their third president in almost 62 years and also announced plans to relocate their headquarters to Washington this summer. Robert G. Smerko, president of the American Wood Preservers Institute in Vienna, will become president following the retirement of Robert L. Mitchell Jr., the institute's president for the past 30 years. The group decided to move to the Washington area because it wants to continue its efforts to "defend" chlor-alkali products to Congress and other regulatory agencies, said Donald S. Pirkle, newly elected board chairman and a vice president and general manager of Dow Chemical USA.

At its annual meeting recently, the Small Business Legislative Council compiled a list of key small-business issues to submit to Congress. The coalition, which is made up of 85 trade association members that represent over 4 million small businesses nationwide, named tax reform, liability insurance, antitrust enforcement, the federal budget and government competition as the most important issues facing small business in America today. At the meeting, the group also elected new officers for 1986: Bruce Hahn, chairman of the National Tooling & Machining Association; JoAnn Price, chairman-elect of the American Association of Mesbics (Minority Enterprise Small Business Investment Companies); Wayne Smith, treasurer of the United Bus Owners of America; Peter Ruane, secretary of the National Moving and Storage Association; H. Ted Olson, vice chairman, Specialty Advertising Association International; and William Maas, vice chairman of Florists' Transworld Delivery.

Buffalo businessman Frank Wilton has been elected 1986 chairman of Washington's Health Industry Manufacturers Association. Wilton is president of Ethox Corp., which manufactures sterilized disposable medical products. Walt Robb, senior vice president and group executive of General Electric's Medical Systems Group, was selected chairman-elect of the association, which represents 300 manufacturers of medical devices and diagnostical products.