Gregory Korte, and Tom Vanden Brook

USA TODAY

WASHINGTON — President Obama issued an executive order Thursday allowing the Pentagon to call up reserve troops to combat the Ebola crisis in Africa.

Obama also opened the door to an Ebola "czar" to coordinate the response, saying that an additional official may be helpful as his advisers juggle threats of terrorism and the upcoming flu season.

And while he said he had no "philosophical objection" to barring west Africans from traveling to the U.S. from western Africa, he said he would continue to listen to experts who say "a flat-out travel ban is not the best way to go."

The Pentagon said it had no immediate plans to send reservists or National Guard troops to Africa, saying that the order simply allows the military to begin planning for those forces in its overall response.

It "doesn't mean that we are deploying these forces, but it gives us the option to do so if we need to," said Air Force Lt. Col. Thomas Crosson, a Pentagon spokesman.

The Pentagon is identifying gaps that active-duty troops cannot fill, said a Defense Department official who was not authorized to speak publicly about the issue. Among the specialists that might be tapped: technical engineering, communication systems, logisticians, comptrollers and religious specialists. .

At least eight engineers have already been identified as possible call-ups. All reservists called to duty will be given proper training and medical-threat briefings, the official said.

The president notified Congress of his order Thursday after phone calls with top congressional leaders of both parties, and to the governors of Ohio and Texas. He also met with top advisers in the Oval Office Thursday evening.

The order reads: "I hereby determine that it is necessary to augment the active Armed Forces of the United States for the effective conduct of Operation United Assistance, which is providing support to civilian-led humanitarian assistance and consequence management support related to the Ebola virus disease outbreak in West Africa.

Obama canceled a second day of political events Thursday in order to deal with the Ebola crisis from the White House, as the second Ebola patient to be diagnosed on American soil was transferred from a Dallas hospital to the National Institutes of Health in Bethesda, Md.

NIH Director Anthony Fauci said Pham will be treated in a special unit "designed to provide high-level isolation'' with staff trained to handle infectious diseases and critical care. He said Pham "is stable, and she seems to be doing reasonably well.''

Public health experts have been dispatched to Ohio after a second infected nurse traveled from Dallas to Cleveland and back last weekend, "It's very important to make sure we are monitoring and tracking anyone who was in close proximity to this second nurse," Obama said.

But Obama said his biggest priority was "dealing with this problem at the source" — the outbreak in Liberia, Guinea and Sierra Leone.

The White House said it didn't know exactly how many reserve troops would eventually be required.

"The president has laid out very clearly what the mission is. The Department of Defense has told the president that it will require about 4,000 Department of Defense personnel to execute the mission the president has directed them to execute," White House Press Secretary Josh Earnest said earlier in the afternoon. "What I don't know is the composition of that force."

At the Pentagon, officials expect as many as 3,000 troops could be sent to Liberia to fight the disease. There are no plans for them to be involved in the direct treatment of victims. Instead, they will build treatment facilities and operate labs.

The Pentagon recently finished building a mobile, 25-bed hospital in Liberia for infected health-care workers, said Army Maj. Gen. Darryl Williams, who commands the Pentagon's task force responding to the Ebola crisis.

The hospital will be staffed by the U.S. Health Service Commission Corps, Williams told reporters on Thursday. Two laboratories are also operating, and troops are constructing 17 treatment centers.If troops are infected by Ebola, they would be quarantined, stabilized and transported out of Liberia for treatment, Williams said. Troops are constantly monitored for signs of the virus, Williams said. On Wednesday, his temperature was checked eight time.

William M. Welch contributed from Los Angeles.

Follow @gregorykorte on Twitter.