The 90,000-square foot project, which saw the East Wing torn down last October, has been the subject of a legal challenge.
Donald Trump has pointed to the upcoming state visit of the King to highlight the need for a controversial 400 million dollar (£301 million) ballroom at the White House.
The US president argued the development was necessary to entertain a large number of people when hosting foreign dignitaries and world leaders.
The 90,000-square foot project, which saw the East Wing torn down last October, has been the subject of a legal challenge in a bid to halt construction.
The White House is sited on federal parkland.
A panel reviewing the plans, which is headed by a top aide to the president, is due to hold a final vote on the scheme on April 2.
Earlier this year, the US Commission of Fine Arts, whose members were appointed by Mr Trump, gave unanimous backing to the proposal.
Speaking to a group of farmers as he overlooked the building site, the president and billionaire developer declared: “I love construction.”
He added: “That’s a big dig. We’re building a ballroom.
“Every president has said can we have a ballroom please, a room where you could have a lot of people?
“So when the president of China, France, when somebody comes over from the UK, including the King, we have the King coming over very shortly, King Charles, so we can have, like, a large room, because the White House is incredible, but it never had a ballroom.
“That’ll be the finest ballroom anywhere in the world when it’s completed.
“I love construction. I love building beautiful things.”
The now-demolished East Wing was originally built in 1902 during Theodore Roosevelt’s presidency and subsequently expanded in 1942 under Franklin Roosevelt.
The privately funded ballroom development, which is designed to hold 1,000 guests, is due to be completed before the end of Mr Trump’s presidency in 2029.
Earlier this week, the president denied transatlantic tensions over the Iran war would affect the King’s planned trip to the US.
There have been calls for the historic royal trip to be scrapped or delayed because of the ongoing Middle East crisis.
The tour has yet to be officially announced, but the King and Queen are expected to visit Washington and New York in April to mark the 250th anniversary of American independence.
