Prospect House, a 13-story North Arlington apartment building with a sweeping view of downtown D.C.'s federal landmarks, has been sold for $23 million to a group already planning to convert to condominium ownership.

Gary Nordheimer confirmed yesterday that Prospect House Associates bought the 268-unit apartment building from a partnership that included developers Lawrence N. Brandt, Donald Brown, Gerlad Miller and Joseph Gildenhorn. The new owners include Nordheimer's brother, Scott; attorney Myer (Mike) Feldman and Cadillac Fairview, a Canadian realty investment firm.

Sen. Howard Metzenbaum (D-Ohio) occupies an exceptionally large view apartment in Prospect House with a lease extending through 1982.Rep. G. V. (Sonny) Montgomery (D-Miss.) also rents an apartment. "I'm thinking about buying it, but the price is high," he said.

Rents and sale prices of view-side apartments are much higher than those for smaller apartments facing the 1200 block of North Nash Street.

Attorney Michael Simpson, who has lived in a $600-a-month view apartment for six years, said he and his wife are interested in purchasing at the "as-is" tenant price of $112,000. However, he said he and other tenants have formed an association that will seek more information and assurances before signing agreements to purchase. Until March 10, prices to tenants will range from under $45,000 to $175,000.

Simpson, who described himself as the in-house attorney for the newly formed tenant association,said tenants need more time, more information and an engineering firm's report on the building.

Nordheimer countered that the engineering report will be made available to prospective buyers this week and that the full condominium conversion documents will not be available to tenants until approved by the Virginia Real Estate Commission.

Nordheimer said two dozen tenants already have signed early reservations with $2,000 refundable deposits and that other former tenants have indicated a desire to return as owners. After April 30 sales are scheduled to be offered to the public.

The 340 exterior and interior parking spaces are being offered at prices up to $9,500. New kitchens are being offered to tenants buyers for $5,500.

The Nordheimer brothers and Feldman, who have handled more than half a dozen District apartment building conversions to condo owneships in the past five years, recently purchased the Georgetown Inn. Among their apartment conversions are the Appoline, 400 Tunlaw and 4200 Cathedral.

About 25,00 former rental apartments have been converted to condominium ownership in the metropolitan areas in the past decade -- most of them in the District and Virginia. In addition, more than 20,000 ned condominium units have been built and sold in this area, mostly in Northern Virginia.

D.C. law requires tenant groups be given the right to meet a developer's purchase price, and a dozen groups have done that. Virginia law has no similar requirements.

In commenting on the sale of Prospect House, developer Brandt said that the rents had tripled in the building over 17 years. He said he plans to build a rental high-rise, view apartment as part of his own Sutton Place condo comples in Northwest and then covert it to condo ownership after a reasonable time.