It has been a year since the Arlington County Board ordered the closing of the 1,100-space parking lot on top of the Pentagon City Metro Station and while the lot remains vacant county officials are convinced that their decision to order it shut was correct.

The lot, just off Shirley Highway south of the Pentagon, is the site of a proposed Pentagon City shopping center, and construction on it is not scheduled to begin until the end of the year.

Meanwhile, predictions of revenue losses and decreased ridership for the Metro subway system seem not to have come true.

While it's not known how most Northern Virginia commuters who used the lot at S. 15th and S. Hayes streets are faring, one of them said he has adapted easily. "It didn't create the hardships I thought it would," said Harry Tyner of Alexandria, who parked at the dirt and gravel lot almost daily until Arlington closed it late last August.

County officials, reacting to complaints about noise and pollution from South Arlington residents, promised to close the lot when Metro's Yellow Line opened beyond Arlington's borders.

That promise was fulfilled almost eight months after the line opened at the Huntington Station in Fairfax County. These days, Tyner said, he's found it more convenient and less expensive to park near the King Street Station in Alexandria. "There's adequate parking there and it's probably closer to where I live," he said.

Metro officials said they have not realized the predicted decreases in ridership at Pentagon City. Metro had warned that the action could result in a loss of $440,000 a year to the transit system and a decrease of as many as 1,800 riders daily.

But transit officials said recently that the average daily ridership at the station had increased slightly, from an average of 2,500 boardings a day in August 1984, to about 2,900 last month. There is no way to determine if ridership at the station would have been even higher if the lot had remained open, an official said.

Many South Arlington residents seem to be pleased that the lot is closed. "In my view, and I think it's shared, there's less fuss and muss down here, less traffic and less dust raising," said John W. Marr, a resident of the Arlington Ridge neighborhood near the stop. "There's been a noticeable effect, a good one."

County Board Vice Chairman Mary Margaret Whipple, who is also the county's representative on the Metro board, said she had no regrets about closing the lot. "We feel our policy of not providing massive parking lots around Metro stations is a correct one," she said. "It encourages people to use mass transit and diminishes traffic congestion.