Some 40 years ago it was considered the ugly duckling downtown, a dated building that needed to be demolished to make way for a new complex of beaux-arts-style federal offices.

Now the Old Post Office Pavilion is primed to become the pinnacle of Washington luxury, a hotel by Donald Trump and his daughter Ivanka outfitted with 271 guest rooms, a massive ballroom, high-end restaurants and two opulent suites in what were once the offices of the postmaster general.

In early August, the Trumps signed a 60-year lease with the federal government for the 114-year-old building, and on Tuesday morning, they unveiled room and meeting space designs that they vowed would make it a destination for Washington power brokers, international visitors and luxury travelers.

Donald Trump repeatedly asserted during 18 months of negotiations that profit was not his driving motive in pursuing the project, and on Tuesday, he likened the Old Post Office to “a great painting.”

“Friends of mine, they spend these ridiculous amounts of money on paintings,” he said. “I’d rather do jobs like this, and do something really that the world can cherish and the world can see and that everyone in D.C. can truly be proud of. And that’s what we’re going to do.”

The overhaul is expected to cost $200 million. Inside the main entrance — a space long occupied by T-shirt and hot dog vendors — the Trumps plan a lobby and lounge with a central fountain, hand-woven rugs and brass-and-crystal chandeliers.

Upstairs, where a few federal agencies operate, the Trumps plan guest rooms averaging the size of a small Manhattan studio apartment: 600 square feet, with 14- to 16-foot ceilings, wool carpets, six-foot bathtubs, and crystal sconces and chandeliers.

Two “presidential suites” are pegged for 3,000 square feet each and will feature private saunas, walk-in closets and views of Pennsylvania Avenue and the Mall.

For the crumbling and vacant rear annex, part of a failed redevelopment attempt in the 1980s, the Trumps have planned what Ivanka Trump said would be the largest ballroom in Washington.

Mayor Vincent C. Gray and members of Congress and the D.C. Council said they hoped the Trumps’ plan would be the end of a 20-year-plus redevelopment effort.

Despite the property’s value to the private sector, previous efforts to rehab it failed. As a result, the General Services Administration, which manages real estate for the federal government, has been paying about $12 million annually to operate the building while collecting only about $5 million in rent.

When the agency offered the project to the private sector in 2011, developers and investors swarmed, proposing ideas including a Waldorf Astoria Hotel and a National Museum of the Jewish People. Donald Trump prevailed in partnership with Colony Capital; he has since decided that his company will be the project’s sole owner and plans to open the hotel in late 2015 or early 2016.

The Trumps will pay $3 million annually in rent, with escalations tied to the consumer price index, on a lease lasting 60 years from the hotel’s opening, with options to extend an additional 40 years. The agencies upstairs — including the National Endowment for the Arts and the National Endowment for the Humanities — are moving out soon, and the National Park Service will maintain public access to the 315-foot clock tower, one of the tallest structures in the city.

Del. Eleanor Holmes Norton (D-D.C.), who has repeatedly pushed and prodded the GSA to put the building to better use, called the Trumps “master developers” whose first project in the city would end a development ordeal that was underway when she took office in 1991.

“They came in the toughest way, by winning one of the most competitive contests for development of a site in my more than two decades in Congress. They have put to rest the saga of the Old Post Office building,” Norton said.

Gray (D) said he expected the project to generate $100 million in tax revenue over 10 years, create 700 construction jobs and lead to 300 permanent jobs in an employment sector, hospitality, that the District has been trying to grow.

Donald Trump said that he was committed to getting D.C. residents into jobs. “We’re going to use as many folks from the area as we can,” he said.

Without mentioning the Hay-Adams, W or the Four Seasons by name, the Trumps are positioning their District property as a needed place for power brokers and A-listers. It will be the Trumps’ ninth hotel. “Most major cities have a distinctive destination when it comes to a gathering power spot, a place where business deals are consummated,” said Betsy Hughes, an associate at design consultant Hirsch Bedner Associates, suggesting that the District, at present, does not.

It remains to be seen how well the Trumps compete with the top incumbent hotel operators, but the sometimes-combative mogul seemed determined not to let politics or controversy get in the way, praising GSA officials and posing for photos with council member Marion Barry (D-Ward 8) and others. “Building is what I do best,” he said. “Better than ‘The Apprentice,’ better than politics. It’s what I do.”

Said Norton: “They know that they are a stone’s throw away from the White House, but they know better than to throw stones.”

Twitter: @oconnellpostbiz