In 1985, Dart Group Chairman Herbert H. Haft stunned residents of an elegant Northwest Washington neighborhood by paying $1.7 million for the English Tudor mansion at 2501 30th St. -- and then demolishing it.

Neighbors knew then that Haft had big plans for the half-acre lot, and now those plans are plain to see.

Last week, a crane hoisted blocks of a prefabricated concrete cornice into place above the entrance to Haft's new home, a princely, renaissance-style palace being built at a cost of more than $4 million. Haft is expected to move there in June.

Some residents believe the house will enhance the enclave of embassies, ambassadors' residences and a few private homes near Massachusetts Avenue, but others say it overpowers the surroundings.

"It's a little mini-Versailles," said Louie Dweck, whose property borders Haft's walled-in backyard.

Fluted columns frame the front entrance of the massive two-story house, and a balustrade adorns the roof. The facade is constructed of custom-molded concrete made to resemble limestone. Its centerpiece is a Palladian window modeled after an original at Mount Vernon, George Washington's colonial estate.

Haft declined to be interviewed about the house, and officials in charge of its design and construction said he has asked them not to discuss it in detail. However, sources familiar with the house described its elaborate interior, which features gold-leafed ornaments and multicolored marble floors.

A grand staircase with a wrought iron and brass railing will rise through a 40-foot-high atrium at the center of the house. A chandelier will hang from a dome atop the atrium.

One of the more lavish rooms is the first-floor library, where gilded capitals top black lacquered columns and mahogany bookshelves will line upholstered walls, a craftsman said. Elsewhere in the house, wooden columns are painted to look like marble, he said.

Antique features include imported fireplace settings and chandeliers.

The two marble-floored master bathrooms are about as large as the master bedroom. A whirlpool tub occupies a bay window in each, and the showers double as steambaths.

The house includes three separate servant's apartments, each with its own bathroom, the craftsman said.

Originally designed to include a third story, the house has the structural supports of a much larger building, which reinforce its aura of permanence.

The E.A. Baker Co. Inc. of Takoma Park is building the house for $4 million, a Baker employee said. That figure does not include the cost of landscaping the terraced yard, installing a swimming pool in the rear, or adding many of the more specialized interior decorations. Nor does it include the cost of furnishing the house.

Haft, who is in his late 60s, now lives in Potomac. He was ranked 397th on Forbes magazine's October list of the 400 wealthiest Americans. The chairman of the board of Dart Group Corp., whose latest venture is an attempted hostile takeover of Stop & Shop Corp., has an estimated net worth of $225 million amassed in retail businesses, real estate and finance. In 1984, the Dart Group sold its namesake, a chain of 73 Dart Drug stores, for $160 million.

From the outside, Haft's new home has evoked a mixture of admiration and disdain. "This thing is gauche. Someone said it was a monument to his {Haft's} own bad taste," said Nell McCracken, a longtime resident who moved out of the neighborhood in late 1986 but returned to visit a friend last week.

"It's too big for the land it's on. It would be beautiful sitting on 50 acres with some sheep grazing on the front yard," she said.

Dweck said, "It's very huge to say the least. It's quite imposing." But she stopped short of offering an aesthetic assessment. "I hate to say anything to hurt the Hafts' feelings."

A 30-year resident of 30th Street, who requested anonymity, gave her new neighbor a nod of approval, however. "It's certainly an addition to the neighborhood and not a detraction," she said.

Haft's sharpest critic, Ribeth C. Appleby, the widow who sold him the Tudor mansion in June 1985, has stayed away from the construction site. "I don't want to see what he's done. I wouldn't go by to see that monstrosity for anything in the world," she said. Appleby, widow of financier James Scott Appleby, still fumes at the memory of her old home reduced to rubble.

She said that had she known that Haft would raze the 30-room house built for the Appleby family in 1926, she never would have sold it to him.