ANKARA, Turkey — President Donald Trump is expected to tell President Recep Tayyip Erdogan of Turkey that he is prepared to restore the country to a program that would allow it to purchase F-35 stealth fighter jets, a move that would reverse a ban Trump himself imposed seven years ago on national security grounds.

But the shift by Trump, who is heading to a NATO summit in Ankara this week and has said he was preparing to bring a gift that would make Erdogan “very happy,” could face opposition in Congress, which could seek to block it.

Four senior administration officials described the coming change in policy, after weeks of behind-the-scenes work by national security officials to break the stalemate. Though officials differed some on the details of how Trump would seek to work around congressional and legal restrictions on his action, they said they expected Trump to at least signal his intent to get the fighter jets into Turkey’s hands — though it is uncertain when.

It is unclear exactly what Trump will say, and officials cautioned that he could change his mind. He is unpredictable even to his own staff. But administration officials suggested there could be an exchange of letters on the subject between the two leaders to get the process underway. When asked for comment, a White House spokesperson pointed to the president’s past comments.