One of Fairfax County's longest-pending development decisions was delayed again last night as the county Board of Supervisors decided to defer until Thursday a resolution of how much building will be allowed around the Vienna Metrorail station.

The end-of-the-Orange-Line station, located in the median strip of I-66 about 12 miles west of the District, is scheduled to open June 7.

The decision to defer came after a weekend of partisan maneuvering, as both Democrats and Republicans sought a way to determine development ceilings while sidestepping any political damage.

Both parties fear that an antidevelopment backlash could appear in coming elections. Each worries that the decision on the Vienna station could galvanize voters' anger about the traffic that accompanies growth.

The county has been struggling to resolve the issue for the better part of two years, but persistent disagreements among citizens groups, developers and local officials have repeatedly fostered postponements.

Last night, Supervisor James M. Scott (D-Providence), who represents the district where the station is located, noted that at least 46 persons were scheduled to speak on the various plans for development. By the time they finished, he said, it would be after midnight.

"I doubt that it's going to be possible to make a rational decision at that hour," he said. The board accepted his proposal to postpone a decision.

Scott announced two weeks ago that he would resign from the nine-member board June 3. A special election to fill his Providence District seat is set for July 15.

Some Democrats speculated privately that Republicans were seeking to gain a leg up in the special election by rejecting a development plan that Scott had been expected to support last night. By voting to keep the current ceiling on development around the station, those Democrats said, Republicans could position themselves -- if only temporarily -- as opposing rapid growth and further congestion in the populous heart of the county.

That image could give the GOP an edge at the special election to fill Scott's seat that could translate into a 6-to-3 majority on the Board of Supervisors. The Republicans now have a 5-to-4 majority.

One of the most ardent opponents of raising the ceiling of development around the station is Charles A. Robinson, the mayor of Vienna, who fears that higher development levels will strangle traffic on the already-congested roads in the area. The Vienna town boundary is just 500 yards north of the Metrorail station.

In a 20-minute speech, Robinson said the decision would have "the greatest single impact on the town of Vienna in the last 20 years."