Tilden Gardens, a cooperative complex of low-rise apartment buildings on Connecticut Avenue, has turned 50. But in a stately, English Tudor sort of way, it looks almost ageless.

Last Saturday most of the residents gathered in the tiered, sprawling central gardens behind the buildings to toast the anniversary with champagne and nonalcoholic punch.

For all the years that this grouping of nine, five-story brick residential buildings has been on the triangle formed by Connecticut Avenue, Sedgwick and Tilden Streets, the site has been regarded as one of the area's most attractive intown residential complexes.

But few Washingtonians, other than neighbors and veteran realty professionals, are aware that the 210 units in Tilden Gardens are cooperatively owned. (Unlike condominium owners, cooperative owners do not own their own apartments: They own a share of the complex with the right to occupy one dwelling.)

Two of the buildings, on Tilden Street, each have only 20 apartments. Those first cooperative buildings developed by Monroe and R. B. Warren were sold before the stock market crash in 1929. Each is a separate small co-operative.

The entire project was envisioned by the Warrens, who were prolific builders in Northwest Washington, as a new-style complex. Elms, maples and oaks enhanced the five-acre tract then and now. Today's most enlightened land planners would likely applaud the Warren plan to leave more than three acres as open space -- creating a large garden area in the back. There are about 40 units per acre in the entire complex.

Any flashback on Tilden Gardens, once home of Sen. Harry S. Truman and Gen. Mark Clark, has to focus on the stock market crash and subsequent economic disaster that hit this country 50 years ago. The Warrens somehow kept their project in motion but were unable to find buyers for the large apartments, which were priced from $13,000 to $18,000 -- with 20 percent down. They completed buildings C through I into the 1930s. But almost all of the 170 units were rented for years.

Helen Dyer, a retired biochemist and long-time resident, recalled at the anniversary party that she and her late mother (who lived to be 98) rented a three-bedroom, two-bath apartment in F building in 1931 for $175 a month. They stayed there until 1939 (when the selling effort picked up with the economy) and then bought a large, two-bedroom apartment in C building, where Helen still lives, for $16,000.

Indeed, there is little turnover. Roy Lykes, president of Tilden Gardens Inc., which administers buildings C through I, said that vacancies occur mainly because of death or the need of an owner to go into a nursing home. Many of the resident-owners are retired, like Norman Sulzbach, and say they love the place.

Lykes, 40, one of the young lads on the block, bought his apartment several years ago because it was large, had 10-foot ceilings and was conveniently located. He is director of stores for W. & J. Sloane.

The original Tilden Gardens mortgage was paid off years ago, Lykes said. Now the owners pay monthly fees ranging from $225 to $425, depending on the size of the apartment, to handle the taxes (now $80,700 annually on land and buildings assessed at $7.9 million), oil-fired steam heat, maintenance and services.

If there are exceptional expenses, special assessments are made. "But we try to hold down costs for fixed-income people," Lykes added.

The few turnovers each year bring more younger couples and single persons into Tilden Gardens.

Ten years ago the complex was charged by the Justice Department with systematically vetoing the purchase applications of blacks and Jews. That suit was settled with a consent order in 1970. The owners, while not admitting any violation of civil rights law, agreed not to discriminate in the future. A non-discrimination clause was put in the Tilden Gardens by-laws.

"Most of us were really unaware whether or not there were any Jewish people in the buildings, but of course we were aware that there were no blacks," Dyer recalled.

"Now we have at least one black owner and how many Jews, I just don't know," the third-generation Washingtonian added.

A Justice Department spokesman said this week that the complex is felt to be in compliance but said no statistics were kept now in its residents.

The Tilden Gardens by-laws do not permit children or pets, which Lykes and Dyer say reflects the long-time consensus of the members of the cooperative, who meet annually to review operations. The same by-laws forbid a member to rent out an apartment.

However, there are a few one-bedroom units -- converted from a former trophy room -- that are available as rentals from the co-operative. And the former dining room in the main building is now leased to the Daughters of the American Revolution as office space.

Residents of Tilden Gardens have no pool, relatively few indoor parking spaces (which are rented), no tennis courts or central air conditioning. Many of the apartments in X-shaped buildings have windows on three sides.

A 50-year-old sales brochure on Tilden Gardens described the site as a "happy mean between urban and suburban life." The adjacency to the National Bureau of Standards was stressed, as were the landscaped gardens. NBS moved to Gaithersburg years ago but the intown location is even more convenient now that Metro service is expected to be available next year.

Edmund C. Flynn, a veteran real estate man whose 90-year-old father was a pioneer in the development and sales of co-operative properties here, reports that a three-bedroom unit with 1,800 square feet of space was recently resold at Tildens Gardens for $95,000. Residents say that is probably the highest price ever paid there. Most two-bedroom units at the complex sell for about $45,000 to $65,000, depending on condition and size.