The Prince George's County Council voted yesterday to support a 90-day test of a plan to alter the flight paths of airplanes taking off from National Airport in an effort to reduce the noise they produce in some areas.

The test, known as the scatter plan, would reduce the amount of noise over such Prince George's areas as Fort Washington and Friendly, which are currently in the line of national's southbound flight path, but would increase the noise in other areas, such as Oxon Hill, according to testimony the council heard yesterday.

A greater number of county residents would be subjected to airplane noise, but no one area would be subjected to the noise of all southbound takeoffs, as is the situation now, said William T. Moran, a member of the Prince George's County Advisory Board on National Airport, which helped draw up the scatter plan.

"The question is, do you want to have the intensity of noise in one area or do you want to scatter it so that everyone in the region gets a little bit of the benefit and a little bit of the noise of National Airport," said council member Richard Castaldi, who proposed the county go on record in support of the 90-day testing.

"Nothing is better. Any direction you go, you're being affected," responded council Chairman Frank Casula. "The only solution to this problem . . . is to close National down."

Casula said the test plan, which the Federal Aviation Administration has said is safe, would also have to be approved by the Washington area Council of Governments, which is expected to vote on the matter next Wednesday. COG would be responsible for surveying residents during and after the test to determine what effect it has on the communities involved.

In other action, council member Hilda Pemberton introduced a measure that would prohibit the sale of junk food to minors by mobile vendors before 10 a.m. on school days.

Pemberton said she has had a number of complaints from parents in her Seat Pleasant area district that children are using their lunch money to buy candy, ice cream and gum from trucks that tour neighborhoods and local schools in the morning.

The council also introduced a bill that would require all public health spas and hot tubs to be licensed and conform to strict guidelines set down by the county.

A measure that would have required all future county employes to reside in Prince George's was killed.

The council also passed a resolution to establish a task force to review the procedures by which child support payments are made.