The Metropolitan Washington Council of Governments board voted yesterday to give most close-in residents of the Washington area an earful of what those who live along the Potomac River hear: the thunderous roar of jets leaving National Airport.

COG proposed a test period during which planes departing National would make low-level turns at full throttle almost immediately after leaving the runways, instead of flying along the river to higher altitudes before turning.

"I think it's extremely likely that we would go ahead and conduct the test," said James A. Wilding, director of Metropolitan Washington Airports, the Federal Aviation Administration agency that runs National. Wilding emphasized that he was not committing himself, but said the FAA ran a similar type of test in 1979 at COG's request and has openly sought its help on National Airport issues.

The earliest the test could be run would be late fall, Wilding said. It could last for 90 to 120 days.

COG's idea is to scatter the impact of takeoff noise instead of concentrating it close to the river. The FAA has evaluated the proposed test, found it safe but noisy, and promised to run it.

The evaluation said that "a portion of the District of Columbia generally north of the Naval Observatory, along with . . . Bethesda and Chevy Chase in Maryland and McLean, Arlington, Annandale and Falls Church in Virginia would experience a measurable increase in departing aircraft overflights and noise impacts. . ." when aircraft take off to the north.

There would be less impact south of the airport, the evaluation said, and most of that would be in Alexandria and far Southeast Washington. There would be less noise for the residents of Cabin John, the Maryland community near the Capital Beltway and the Potomac, which now get the brunt of jet noise when planes take off to the north.

There would be no change in flight patterns for incoming planes.

FAA officials said the plan would bring no significant relief to the residents of Southwest Washington, who already get an earful when northbound flights take off up the Anacostia River instead of the Potomac. That particular pattern is flown frequently by both Eastern Airlines and New York Air as a fuel- and time-saver on trips to New York.

COG asked the FAA last December to develop a test program, which it did. A counterproposal was offered by a group known as the Metropolitian Area Coalition on Airport Problems and the Prince George's Advisory Board on National Airport Operations, and it was that counterproposal the COG board recommended yesterday.

It specifies that aircraft taking off to the north would fly for two miles to an altitude of 1,500 feet, then turn their destination. Aircraft taking off to the south would fly three miles to 1,500 feet before turning.

Currently, jets taking off to the north (with the exception of those flying up the Anacostia) generally fly upriver to Cabin John, a distance of about 10 miles, before turning. Jets taking off to the south cross the Woodrow Wilson Bridge, a distance of about five miles, before turning. Weather and air traffic conditions sometimes force changes in those patterns.

The COG board also reiterated yesterday its long-held position that the best way to alleviate the noise problem at National is to transfer many flights to Dulles International Airport. The FAA has the entire National-Dulles matter under study and has promised a plan for both airports sometime this summer.