Salvadoran President Jose Napoleon Duarte, who received treatment here for terminal cancer, will return to El Salvador on Monday and resume his presidency, a Salvadoran official said on Friday.

Salvadoran Ambassador Ernesto Rivas Gallont said Duarte would meet President Reagan at the White House before boarding an American plane at Andrews Air Force Base outside Washington for the return trip home.

"Physically, he's very strong," Rivas Gallont said. "They will release him from the hospital probably tomorrow and he will have to come back in three or four weeks for more chemotherapy treatment."

Duarte, 62, underwent surgery on June 7 at Walter Reed Army Medical Center. Surgeons removed two-thirds of Duarte's stomach but found his liver was also infected by cancer which was inoperable.