A Reston-based subsidiary of Mobil Corp. has announced plans to retain for the next five years about half of the 1.095 units in Colonial Village Apartments in Arlington as rental units. Plans for the rest of the complex, the first Federal Housing Administration-financed garden apartment complex in the country, are under study, according to a Mobil official.

The announcement ends months of speculations about Mobil's intentions for the red-brick garden apartment complex described by Arlington officials as usually attractive and well-maintained. Rents at Colonial Village, which was built in 1935, range from $170 for a one-bedroom unit to $220 for a two-bedroom unit.

The plan, which Mobil official James Todd called "conceptual," was presented at a recent meeting of the Colonial Village Ad Hoc Committee, an eight-member group composed of tenants, Arlington County Planning Commission members and Mobil representatives.

"It's a trial balloon as much as anything." said Planning Commission secretary Gary Kirkbride of the announcement. Todd said the plan was formulated at the committee's request. "They pushed us for a plan. We weren't originally planning to move this fast," he said.

Todd said that plans for the rest of the 55-acre complex, located midway between the Rosslyn and future Courthouse Metro stations on Wilson Boulevard, are under study by Mobil.The 585 units Mobil plans to retain are located in the area generally bounded by Wilson. Queens Lane, Key Boulevard and N. Uhle Street. Also included in the complex are about 15 acres of undeveloped land.

"Mobil is trying to figure out what to do with the remainder of the units, whether it is economically feasible to preserve them, tear them down and replace them or put up mid-rise or high-rise buildings" in the area nearest the Courthouse Metro station, Kirkbride said.

Todd said it is unlikely that any redevelopment would begin before 1980.

At a meeting last week the board of directors of the Colonial Village Tenants Association directed the two tenant members on the Ad Hoc Committee to reject Mobil's proposal. Tenant committee member Raymond Lewis Lewis said he planned to tell Mobil representatives at a meeting scheduled to be held today that the Association favors preservation of all of Colonial Village.

Another tenant group, the Colonial Village Preservation Committee, is seeking to have the complex designated an historic landmark by the Arlington County Board.

The first in a series of hearings on that proposal is scheduled for Oct. 25, to be preceded by a candlelight march by tenants to the county courthouse.

According to Kirkbride, a historic designation, which Todd said Mobil opposes, would mean that, "If Mobil wanted to change a building in any way, take down a shutter, paint, do repair work, they would have to apply for a permit."