For six decades, the stately 30-room English Tudor mansion near Embassy Row was filled with elegant furnishings and festive parties. Gardens and miniature train tracks covered the half-acre lot at 2501 30th St. NW, and a fleet of Bentleys and Rolls-Royces often lined the drive.

The sun shone through six stained-glass windows onto an intricately carved oak staircase. Pink marble mantelpieces flanked a formal living room, and a drawing room was paneled with Philippine mahogany installed by the same craftsmen who decorated the exclusive Pullman train cars.

When the field stone house was sold June 20 for $1.7 million to Washington retail magnate Herbert H. Haft, it was expected that it would be enjoyed for its grandeur.

Instead, the mansion was razed in July.

"It was one of the nicest houses I've wrecked in years," said Gilbert Fisher, whose accomplishments include the demolition of some of the city's oldest buildings.

The mansion's demise took neighbors, real estate agents and its former owner by surprise.

"I drove by there . . . and I was talking on my phone in the car," said real estate agent Michael Sullivan. "I screamed 'Oh my God!' There was an empty lot!"

Sullivan represented Ribeth C. Appleby, widow of wealthy financier James Scott Appleby, in the cash sale. Appleby lived in the house until it was sold and expressed shock at the razing.

"I would never have sold that home if I had known he was going to tear it down," she said. "In a thousand years I would never have sold it."

Eventually, a new three-story "classical" residence will be built on the lot, said architect Leon Chatelain III, who is designing it. He said the structure, including an outdoor swimming pool, will cost at least $2 million and possibly as much as $4 million when completed.

The old mansion still had much of the original plumbing and was generally not in excellent condition, Chatelain said. The stained-glass windows, marble mantelpieces and other interior fixtures were auctioned off before the house was torn down.

Haft, who now lives in Potomac, had "no comment" on why he bought the place and then brought in a wrecking crew.

The house, built for the Appleby family in 1926, was just north of Rock Creek Park and a block off Massachusetts Avenue. It was the top residential sale in the District during the second quarter of 1985, according to Rufus S. Lusk & Son Inc., a real estate information service. The assessed value, according to 1985 Lusk figures, was $254,307 for the 23,182-square-foot lot and $765,416 for the improvements.

Comparatively, the top second quarter residential sale in Montgomery County was $950,000 for 5216 Abingdon Rd., Bethesda, according to Lusk statistics. The home was sold by M.C. Sanger and others to William E. Minshall.

The top residential sale in the same period in Fairfax County was $850,000 for a newly-built home at 7523 Old Dominion Dr. in the Laurelmont section of McLean. The home was sold by builder Eugene J. Cullinane to Jeffrey M. Bucher.

The purchase price of the old mansion was equivalent to about one-third of Haft's $5.5 million salary last year, earned from his post as chairman of Dart Group Corp. The corporation, according to Securities and Exchange Commission records, is a $256 million holding company that includes 34 percent of Crown Books Corp. and 66 percent of Trak Auto, a discount car-parts franchise. The namesake of the parent company, a chain of 73 Dart Drug stores, was sold for $160 million in 1984.

Local preservation officials lamented the passing of such a structure, but said it could not be prevented because the house, though situated near three historic districts that protect buildings in Georgetown, along Massachusetts Avenue and bordering Rock Creek Park, was not itself a landmark. Without such a designation, a house can be razed without prior public notice, according to Patricia Wilson, architectural historian for the District.

About the only advice Wilson could offer in such situations was this: "If you don't want your house demolished, you don't sell it to someone who's going to demolish it."

Neighbors voiced surprise at the bulldozing in what is usually a stable, quiet residential area.

"People in the neighborhood will miss the house," said Frances Parrish, who lives across the street from the Haft lot. "It was very attractive. It was built in the days when they didn't build them overnight."

Barbara Davy, Haft's agent, said her client may not have been thinking about a new house until after the deal was closed. But, she added, even without the old house, "It's a beautiful piece of property."