A controversial plan for changing National Airport's flight patterns to scatter aircraft noise more widely over residential areas was overwhelmingly opposed yesterday by the Washington region's Transportation Planning Board, an influential panel of state and local government officials.

The 26-member board, which serves as a transportation policy arm for the Metropolitan Washington Council of Governments, was the first regional agency to challenge the new plan, proposed earlier this month by the Federal Aviation Administration. The FAA owns and operates National Airport.

The Transportation Planning Board's vote, with only two members dissenting, also was a further indication of mounting opposition to the proposed fight patterns. The FAA's proposal has already been attacked by the Arlington County Board, Alexandria City Council and Fairfax County Board of Supervisors.

Last week the issue stirred sharp debate among members of the Council of Governments' board of directors. The council, which initially urged the FAA to conduct a test of the proposed flight plan in 1981, is expected to take another vote next month, and its outcome now appears uncertain. The proposal is also being debated by the D.C. City Council and other local governments.

During yesterday's Transportation Planning Board meeting, Arlington County Board member Mary Margaret Whipple led the assault on the new flight plan, arguing that it would expose a large number of Washington-area residents to excessive noise from low-flying jets and that it raised possible safety issues.

She was joined by D.C. City Council member Frank Smith Jr., who represents a central city ward likely to be traversed by jets under the plan. Smith objected to the FAA's proposal for a 60- to 90-day test of the new flight patterns next fall, saying, "Exposing 200,000 people unnecessarily for 90 days is too long."

Under current flight patterns, 551,000 Washington-area residents, most of them living along the Potomac River corridor, are estimated to be exposed to 75 decibels of aircraft noise--a loud enough sound for a person to recognize that it is caused by a jet--for more than 30 seconds daily. Under the new plan, the total number of persons exposed to such noise would rise to 871,000, an increase of 320,000 persons, according to FAA estimates.

However, the FAA says, some neighborhoods that now are exposed to severe jet noise would get some relief. The agency has also termed the plan safe and said it would save 2,400 gallons of fuel a day by shortening jet routes.

An FAA official said after yesterday's meeting that his agency would review the issue further before initiating the proposed test.