The Washington Metropolitan Council of Governments (COG) voted yesterday to recommend that the Federal Aviation Administration test a controversial plan that would subject 320,000 more area residents to noise from low-flying jets taking off from National Airport.

The FAA will make the final decision on whether to test the plan to scatter aircraft noise, but area officials said yesterday that the agency is likely to follow COG's decision. The test could begin this fall and last for 60 to 90 days.

Yesterday's 15-to-8 vote was the second time in two years that COG has supported a test of the plan to divert low-flying aircraft from the Potomac River corridor over residential areas that now hear little, if any, jet noise. The FAA was going to test a noise scatter plan in 1981, but preparations were put off with the onset of the air traffic controllers strike.

"We said we would pay a lot of attention to COG as we did in 1981, but we have always kept that last step," James Wilding, director of National and Dulles International Airports said yesterday.

On Tuesday, the District government became the fourth local jurisdiction to vote against any change in aircraft routes, joining Arlington and Fairfax counties and Alexandria. The Prince George's and Montgomery county governments had voted in favor of the scatter plan test.

When it came down to a vote by the COG board, where the number of representatives from each jurisidiction is based on population, the opponents of the plan did not have the votes necessary to block the test.

Despite the District government's vote against the plan, three of the city's four representatives to the COG board voted in favor of the test.

"This is only a test, not a plan," said D.C. Council member H.R. Crawford (D-Ward 7) who voted for the test. Pauline Schneider and John E. Touchstone, both of whom represent Mayor Marion Barry on the COG board, also voted for the test.

Council member Nadine Winter (D-Ward-6), who voted against the plan at the COG meeting, said, "I haven't heard from anyone in the District who asked me to vote for it. . . . " Winter described the scatter plan as a "Band-aid approach" to the problems of overuse of National Airport.

Prince George's County Council member Frank P. Casula, a member of the COG board and a supporter of the scatter plan test, said he thought it would be "ridiculous" for COG to abandon the test now after pursuing it for two years.

The test would allow jets to make their turns near Key Bridge and the Wilson Bridge; of current rules route them upstream to the Cabin John area and downstream to below the Wilson Bridge before turning. The test, FAA officials acknowledge, would add 320,000 people to the 551,000 area residents who are already subjected to at least 75 decibels of aircraft noise for more than 30 seconds a day.

Parts of Southwest Washington and parts of Northwest Washington, such as Foxhall, Spring Valley, Cleveland Park and the Petworth areas, would be exposed to "increases in significant noise," according to a recent FAA study.

Under the test, the same would be true for Falls Church, Clarendon and North Arlington.

FAA officials said, however, that the residents of the Cabin John area in Maryland and the area north of McLean in Virginia, as well as some areas along the Capital Beltway on both sides of the Potomac River, would probably notice a decline in departing flights over their areas.

FAA spokesman David Hess said a final decision on whether to proceed with the test won't be made until after July 20, when the FAA closes its period to receive public comment on the issue.