The Mobil Corporation disclosed plans yesterday to develop Arlington's 55-acre Colonial Village garden-apartment complex into a mixture of condominiums, cooperative apartments and high-rise office buildings.

The firm said it would preserve the red brick exterior of about 742 units of the 1,100-unit project, keep some of the 12 acres of open space and reserve for a five-year period about 585 rental units for current tenents who cannot afford to buy into the development.

Colonial Village is located only three miles from downtown Washington, midway between Rosslyn and Clarendon. Mobil announced its plans before the county-sponsored Colonial Village Site Plan Review Committee and sent a letter outling its proposals to all tenants.

Mobil's plans still must be approved by the Arlington County planning staff, which will hold public hearings. Construction is not expected to begin until next year.

Under the company's proposals, the rental apartments will not be renovated during the planned five-year period to avoid rent increases. Current residents will not be forced to move out because of conversion, renovation or construction, Mobil said in its letter.

"We don't know what the demands for condominium plans will be," Mobil attorney Martin D. Walsh said. He cautioned that plans at this point are "very, very general."

Other aspects of the plan include: Tearing down 128 apartments in an area bounded by N. Veitch, N. 10th, N. Uhle streets and Key Boulevard to clear over 1 million square feet for office development near a future Metro subway stop. Removing 75 apartments in an area bounded by N. Veitch, N. 18th, N. Uhle streets and Key Boulevard to make way for a high-density residential building up to 12 stories high. Using largely undeveloped land on the perimeter of the tract to develop low-rise townhouses and 12-story apartment buildings.

Members of the Colonial Village Tenants Association generally were pleased by the results of yesterday's meeting.

"My first response is that it (the site plan) looks pretty good," said Dineene O'Connor, vice president of the association. "It looks as if 70 percent of the village is intact."