The Pentagon has instructed defense officials to use the acronym ISIS, not ISIL, when referring to the Islamic State, abandoning the convention of the Obama administration and embracing the term preferred by President Trump.

In a memo signed last week, a senior Defense Department official informed military departments to adopt the new term as they communicate about the ongoing campaign against the militants, spanning from Libya to Afghanistan. The Pentagon’s adoption of the term signals the military bureaucracy is getting in line with the new leadership at the White House, which has indicated a strong preference for ISIS, short for the Islamic State of Iraq and Syria, not the alternative English acronym ISIL — the Islamic State of Iraq and the Levant.

Since even before he declared his candidacy for president, Trump had assailed his predecessor, President Barack Obama, for his use of ISIL — something he said bothered people. “The only one that says ISIL is Obama . . . just not a good person,” he said of Obama in 2015.

Some observers have speculated that the Obama administration eschewed the term ISIS because it wanted to avoid mention of Syria, a country whose long and bloody civil conflict vexed the Obama White House for nearly six years.

The new order reflects the way in which the English rendering of the group’s Arabic name — al-Dawla al-Islamiya fi il-Iraq wa al-Sham — has taken on political meaning going far beyond a debate over simple translation. How that last Arabic word, which can be identified as the Levant, Syria or Damascus, is translated remains at the heart of that debate. The Levant refers to a larger area on the eastern end of the Mediterranean, encompassing Syria and also Lebanon and other countries.

In a sign of its global ambitions, the militant group renamed itself simply the “Islamic State” after it burst onto the scene in the summer of 2014.

In addition, some U.S. military officials have preferred to use the Arabic term “Daesh” — the Arabic acronym for the same term — out of deference to Arab allies who contend the term irritates the militants.

Capt. Jeff Davis, a Pentagon spokesman, said the adoption of ISIS was intended primarily for use in written communications, pointing out to reporters that he had used different terms interchangeably during the course of a single media briefing this week.

The change comes to light as the Trump administration prepares to debate a new Pentagon plan for combating the Islamic State, one that officials hope will map a course for the final defeat of the group in Iraq and Syria. Senior officials are expected to meet Monday to discuss the initial version of that plan.