WASHINGTON — The Pentagon has sent an additional 130 military advisers to northern Iraq to help plan the evacuation of thousands of displaced people trapped by Sunni militants on Mount Sinjar, Defense Department officials said Tuesday, raising the possibility that a larger American force may eventually be needed in the rescue attempt.

While military officials said the Pentagon planned to continue aid drops of food and water, United States officials said they believed that some type of ground force would be necessary to secure the passage of the stranded members of the Yazidi group. The military is drawing up plans for consideration by President Obama that could include American ground troops in what is expected to be an international effort to rescue the refugees, a senior administration official said.

Mr. Obama has insisted, most recently on Monday, that he will not send American ground troops back to Iraq. But as the Yazidi crisis has deteriorated, American officials say they have become increasingly convinced that a humanitarian corridor will have to be established soon, with troops on the ground to help ensure safe passage for the displaced.

Asked Wednesday if there was any way to get the Yazidis off the mountain, Secretary of State John Kerry said, “That’s exactly what we are assessing.”