President Trump plans to divert an additional $7.2 billion in military funding for the construction of a wall on the southern border, according to two people familiar with the plans, as officials rush to show major progress on his signature campaign promise in time for the 2020 election.

The money would be stripped from Defense Department construction and counterdrug projects, the officials said, and amounts to even more than the billions the administration transferred from the Pentagon last year to pay for Mr. Trump’s border wall.

Congress allocated a fraction of that in December in the 2020 budget for border barrier construction — just $1.375 billion. But there were also no limitations placed on Mr. Trump’s ability to transfer funds from Pentagon accounts. The administration has now allocated more than $18 billion for Mr. Trump’s border wall.

The funding would allow the administration to complete more than 880 miles of border wall by 2022, the officials said. But Mr. Trump is still far behind on his promise to deliver 450 miles of wall by the end of this year. Just last Friday, the acting homeland security secretary celebrated the completion of 100 miles of border wall, much of it on land already owned by the federal government.