The Arlington County Board yesterday reopened the question of building a parking lot at the Pentagon City Metro station where more than 500 subway commuters had been parking until the County Board outlawed the practice.

The Board agreed to hold a new public hearing on the controversial issue, after several citizens complained Pentagon City Metro parking had not been adequately publicized to give opponents of the parking ban a chance to air their views. The action raised the possibility that the Board may reverse itself and allow commuters to park near the station.

The Board voted 3 to 2 July 30 to ban further parking on an empty field near the station south of the Pentagon. A ditch was dug along one side of the lot to keep the cars out. Since then commuters have been parking wherever they can in the South Arlington neighborhood.

By voting to ban commuter parking, the Board agreed with residents of the area who argued that the additional number of cars was exacerbating the pollution and traffic problems.

John O'Neill, a member of the County Transportation Commission, remarked after the vote to reopen the issue that the Board was establishing a precedent it would have to pay for later. He said that when a new subway line serving Arlington opens in 1979 parking would also have to be provided near the five stations along it.

In his appreance before the Board, O'Neill asked what would happen after 1980 when development of the Pentagon City area eats up the vacant land?

Glenda Miller, a citizen, urged the Board to provide parking at the station built to serve an area of South Arlington where a massive development called Pentagon City is planned. "Why was there a station built there if there is no way to get there? There certainly is no bus service there."

Only Board member Dorothy Grotos voted against holding further hearings on the issue at yesterday's Board session. Both John W. Purdy, vice chairman of the Board, and Ellen M. Bozman, who along with Grotos had voted earlier to ban parking, favored reopening the issue.

Grotos said many South Arlington residents feel that their community is being used as a parking lot by commuters from other areas who transfer to Washington.

However, a study submitted to the Board yesterday by Arlington County Manager W. V. Ford showed that 51 per cent of the cars that formerly parked at the dirt lot were registered in Arlington. The study said 16 per cent were registered in Alexandria, 14.5 per cent were from Fairfax, and the remaining 18.5 per cent came from other jurisdictions and states.

The study also found that because of the parking prohibition rediership had declined at the Pentagon City Station.

In another controversial matter, the Board late yesterday afternoon adopted a resolution that instructed the county manager to continue collecting information on the sewer problems at Fairlington Villages, where residents claim that sewers in the condominium project have backed up 300 times in the past two years.

The resolution also instructed the county manager to review state laws governing condominiums and sewers so the Board can determine what powers it has to deal with the problem.

In addition, the resolution, worked out between city officials and an ad-hoc committee of Fairlington residents, called on the county manager to inform the Board about any plans for the issuance of ooccupancy permits for about 400 as yet empty units in North Fairlington.

The ad-hoc committee had asked the sewer problems in South Fairlington that the permits not be granted until were resolved, but the Board refused.