A Washington development company announced yesterday that it plans to purchase the four-building, 1650-unit Arlington Towers apartment complex in Rosslyn, on the triangular property bordering Arlington Boulevard, North Lynn Street and Wilson Boulevard, for an undisclosed sum.

The firm, consisting of the Nordheimer Bros., Meyer Feldman and an O & Y Equity Corp. associate, gave no immediate plans for the property, which was built in 1955 and was one of the first high-rise apartment complexes in Northern Virginia.

Ed Brandt, Arlington's housing supervisor, said yesterday whatever decision the developers make could affect the county's critically short supply of rental housing, especially if the apartments are converted into condominiums. "That's (condominium conversion) certainly not out of the question," he said.

"We've got approximatley 40,000 apartments in Arlington County, and 7,500 have already converted or are in the process of converting or selling," said Brandt. "We have another 3,000 that are going condo or co-op, and then in excess of 25 percent (of the county's apartments) will be condominiums."

Should Arlington Towers go condo, Brandt said it will continue the effects of mass condo conversions, which are "pumping up the costs of housing." e

"When a unti converts to condo, it at least doubles the costs per month and probably comes close to increasing the costs two and a half times. Everybody is looking for a tax shelter. . . Everybody is out to buy something, and you can see what that does to renters."

Brandt noted that 1979-80 say a "big upsurge" in area condo conversions, with about 1,500 units converted in 1979 and around 1,200 conversions in 1980. He had no figures on this year's conversions, but said they were "running at that level or higher."

Suzanne Ives, a company spokesman, said the developers plan to reach a settlement by the end of the year. They will not make any plans for Arlington Towers until residents of the complex are consulted, she said.

"They distributed a letter to tenants this morning asking for them to give input," said Ives.