WASHINGTON - Under pressure to select an Ebola "czar" to lead the U.S. response against the disease, President Barack Obama conceded Thursday it "may be appropriate for me to appoint an additional person" to head the administration effort.

President Barack Obama speaks to the media while meeting with members of his team coordinating the government's Ebola response, in the Oval Office of the White House Thursday, Oct. 16, 2014. AP / Jacquelyn Martin

Obama also said he is "not philosophically opposed" to a travel ban from the Ebola-afflicted region of West Africa "if that is the thing that is going to keep the American people safe." But he said experts tell him a ban would be less effective than measures currently in place.

He said his team of Ebola advisers is doing "an outstanding job." But he said several of them, including Centers for Disease Control director Thomas Frieden and Lisa Monaco, his top counterterrorism adviser, are also dealing with other priorities. He noted that Frieden is also dealing with flu season and Monac, with the Islamic State extremists in the Middle East.

"It may make sense for us to have one person ... just so that after this initial surge of activity we can have a more regular process," he said.

Calls for Obama to institute a temporary travel ban grew Thursday, mainly from Republicans who said the growing outbreak in Sierra Leone, Guinea and Liberia are creating a greater traveling threat.

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But Obama said a ban could increase the instance of travelers avoiding detection.

"They are less likely to get screened and we may have more cases of Ebol

a rather than less," he said.

Earlier Thursday, Freiden underwent a series of stern questions from Republican lawmakers on Capitol Hill who wanted the travel ban. But he agreed with the president that such a move could be counterproductive.

"If passengers are not allowed to come directly there is a high likelihood that they will find another way to get here, and we won't be able to track them."

But the president emphasized that dealing with the Ebola outbreak in the nations where the disease is most rampant is the best way to protect the United States from a major outbreak.

"The most important thing that I can do for keeping the American people safe is for us to be able to deal with Ebola at the source, where you got a huge outbreak in West Africa," Obama said.

Obama spoke at the end of a meeting with Health and Human Services Secretary Sylvia Burwell, Centers for Disease Control and Prevention director Dr. Thomas Frieden and top White House officials.

Obama on Thursday also authorized the Pentagon to call up reserve and National Guard troops if they are needed to assist in the U.S. response to the Ebola outbreak in West Africa.

Obama signed an executive order that allows the government to call up more forces and for longer periods of time than currently authorized. There is no actual call-up at this point.

The U.S. has committed to send up to 4,000 military personnel to West Africa to provide logistics and humanitarian assistance and help build treatment units to confront the rapidly spreading and deadly virus.

Separately, Obama placed phone calls to House Speaker John Boehner, House Democratic leader Nancy Pelosi and Senate Majority Leader Harry Reid to discuss the administration's response to the disease.

He also called Ohio Gov. John Kasich to discuss steps the administration took after a Dallas nurse traveled to the state over the weekend before being diagnosed with Ebola, a Kasich spokesman said. The nurse was one of two health care workers who became ill after treating a Liberian man with Ebola at a Dallas hospital.

Obama canceled a Thursday campaign trip to stay at the White House and focus on Ebola. It's the second day in a row he nixed a planned trip because of the outbreak.

In other developments on Thursday, Nina Pham, 26, the first nurse who cared for Thomas Eric Duncan before he died of Ebola was being transported to the NIH center in Bethesda, Maryland, which has one of four isolation units in the United States. She walked under her own strength from the charter plane carrying her into the waiting ambulance.

Nurse Nina Pham arriving in Maryland for care at the National Institutes of Health CBS News

A second nurse who tested positive, 29-year-old Amber Joy Vinson, has been transferred to a biohazard infectious disease center at Emory University Hospital in Atlanta.

Federal health officials said Thursday they still don't know how the nurses caught the virus from Duncan. But a nurse who did not care for Duncan, but did take care of Pham after she was diagnosed criticized the hospital where they work, Texas Presbyterian.

"I saw a chaotic scene," Brianna Aguirre told CBS News correspondent Anna Werner. "It wasn't organized, it wasn't safe, no one really in charge. I went round and round and round with my hospital over who's in charge and the final answer is: I was."

Aguirre said she saw breaches of infection control principles and medical staff being ordered to perform unsafe tasks.

Meanwhile, Frontier Airlines is expanding the circle of passengers being notified that they flew with a nurse who later tested positive for Ebola, or flew on a later flight using the same plane. The airline said that it would contact passengers on seven flights, not just the two flights the nurse took.

The airline put two pilots and four flight attendants on paid leave for 21 days - health experts consider that the outer limit of how long it would take someone exposed to Ebola to become sick.

Frontier's president, Barry Biffle, said that "a handful" of customers have called to cancel reservations since news broke about the nurse's travel on Frontier flights, and that the airline dropped a fare sale scheduled for this week.