In an effort to demonstrate their political power, more than 100 senior citizens packed the Arlington County Board meeting last Saturday to protest the planned decentralization of the senior adult recreation program, originally scheduled to take effect Jan. 1.

The senior citizens' program, which is under the aegis of the county's recreation department, provides recreational and social activities for Arlington's 26,000 elderly residents - an estimated 17 per cent of the county's population - who, in the words of one, "would otherwise sit home and worry."

The senior citizens told the Board that they were very satisfied with the current program, which is directed by one specialist. They said they feared that decentralization and reassignment of the decision-making power from one director to the heads of various community centers would be disastrous.

James E. "Mac" Magruder Sr., one of the group's leaders, urged the Board members to delay the proposed changed pending further study of the reorganization.

"We have the best senior program in the state," he said, noting that it has been used as a model by other jurisdictions. "We see no reason for making any changes in it. We have supported this Board . . . and we are voters."

Board member Dorothy T. Grotos recommended that the program change - part of a long-range plan to reorganize the recreation department which was adopted by the County Board in 1969 - be scrapped. Her statement was greeted by loud applause from the audience.

Board chairman Joseph S. Wholey, who had proposed appointing a task force to study the matter countered, "It's very easy to say nothing will change. I'd like to make the program better."

The Board unanimously adopted Wholey's motion that the Jan. 1 reorganization be delayed pending a report to the Board by a citizen's committee. The report is scheduled to be presented next February.

The Board also heard a status report by community affairs director William L. Hughes on the sewer backups which have recently plagued some residents of the recently renovated Fairlington Villages townhouses.

Hughes said that no certificates of occupancy have been issued for any units since Sept. 10 when the Board ordered an investigation. Several weeks ago Hughes directed his staff to post flourescent stickers on the doors of 400 unsold and unoccupied units that advised prospective buyers that occupancy is illegal until a certificate has been secured.

Approximately 160 units are now awaiting certification, Hughes said. Issuance is being delayed while Hughes and his inspection staff contact present residents and former tenants about the incidence of backups and experiment with equipment used to clean out sewer lines.

Hughes also told the Board that his investigation had convinced him that "the maintenance practices of CBI Fairmac and the Grady Corp. (maintenance agents for Fairlington) need to be scrutinized."

In other action the Board voted 3-2 to grant a request by McDonald's Restaurants to build a four-story contemporary restaurant - without the traditional large golden arches or additional parking - on vacant land located between N. Lynn and N. Moore streets near the Rosslyn Metro station.

Deliveries will not permitted between 6:30 a.m. and 6:30 p.m. on weekdays to minimize traffic congestion in the area of the restaurant.