Volunteers in Centennial, Colo., load medical supplies last week bound for Sierra Leone to combat Ebola. Associated Press

WASHINGTON—President Barack Obama plans to dramatically boost the U.S. effort to mitigate the Ebola outbreak in West Africa, including greater involvement of the U.S. military, people familiar with the proposal said.

Mr. Obama is expected to detail the plan during a visit Tuesday to the Centers for Disease Control and Prevention in Atlanta, these people said. Among the possible moves: sending additional portable hospitals, doctors and health-care experts, providing medical supplies and conducting training for health workers in Liberia and other countries.

Mr. Obama also is expected to urge Congress to approve the request he made last week for an additional $88 million to fund his proposal.

“There’s a lot that we’ve been putting toward this, but it is not sufficient,” Lisa Monaco, Mr. Obama’s counterterrorism adviser, said in an interview Sunday. “So the president has directed a more scaled-up response and that’s what you’re going to hear more about on Tuesday.”

The strategy has four components: control the outbreak at its source in West Africa; build competence in the region’s public-health system, particularly in Liberia; bolster the capacity of local officials through enhanced training for health-care providers; and increase support from international organizations, such as the United Nations and the World Health Organization.

Mr. Obama plans to use a gathering of world leaders at the United Nations next week to seek commitments of funds, materials and health workers for a more robust international response.

The Ebola outbreak has infected at least 4,784 people as of Sept. 12, with 2,400 of them dying—a jump from 3,707 cases and 1,848 deaths as of Aug. 31. The true toll probably is much higher, the WHO says.

The Obama administration has grown increasingly concerned in the last two weeks, as infectious-disease and public-health experts warned that the global response is inadequate to subdue an epidemic that has spiraled out of control, and that it threatens the U.S. and other countries, not just West Africa.

Mr. Obama ordered a bolder U.S. effort about two weeks ago after CDC Director Tom Frieden briefed the White House on his findings from a trip to West Africa, senior administration officials said. Dr. Frieden said publicly on Sept. 2 that he saw dozens of patients lying on the ground in an Ebola treatment center because there weren’t enough beds. “I could not possibly overstate the need for an urgent response,” he said.

Mr. Obama’s plan is a reaction to concern that the epidemic could significantly grow in West Africa, particularly in urban areas. Administration officials stress that the chances of an outbreak in the U.S. are low.

One rising concern among officials is the possibility that the virus could mutate in a way that would make it more dangerous.

The more the virus spreads from one human to another, the more opportunities it has to mutate, virologists say. While not all scientists agree that significant mutations that would change the way the virus is transmitted are likely, one recent study of virus samples over three weeks in Sierra Leone found many mutations.

While an administration official said a dangerous mutation of the virus is unlikely at this stage, “that is a concern that is motivating us to, and the international community more broadly, to get involved even more so now to bring this under control.”

The CDC has at least 105 staff in West Africa—one of the largest deployments in CDC history—tracking down people who have been exposed to Ebola, conducting education campaigns, and other tasks. The government has spent more than $100 million on the outbreak since March, and recently committed an additional $75 million in funding, according to a U.S. Agency for International Development official. The money is used to deploy staff and deliver supplies, such as chlorine and water, as well as hospital beds.

The U.S. military has sent eight service members to the region, including doctors, a logistician and medical specialists. It also said it would send a 25-bed portable hospital unit to Liberia to help care for health workers, but it isn’t planning to staff it. Many public-health and infectious disease experts have called for a greater U.S. military role, which is highly valued in humanitarian crises for its ability to command and control large operations, as well as its logistics expertise.

U.S. defense officials have ruled out sending hospital ships or the big-deck amphibious ships that frequently respond to humanitarian disasters. One official said if the virus got aboard one of those ships, it could quickly spread and would be difficult to stamp out.

These experts say that is what is needed in West Africa, because the governments of the three most affected countries—Liberia, Sierra Leone and Guinea —have been overwhelmed and their health-care systems have all but crumbled. The crisis also has become too large for aid organizations and health ministries to handle alone, they say. The current response, involving several local and international agencies and organizations, also lacks coordination.

The military could be used to direct supplies, set up tent hospitals, and tap the masses of medical personnel that are needed globally to get the sick into isolation and treatment, so they stop spreading the disease to others and improve their chances of recovery. Now, there are so few hospital beds that many are having to suffer through the disease at home, where they risk spreading it to loved ones.

And while hundreds of millions of dollars in aid have recently been pledged, under current circumstances it won’t arrive in West Africa for weeks – by which time thousands more will be infected and dead.

Mr. Obama hopes to begin to turn the situation around with the rollout of his new strategy, administration officials said.

“We think these measures, this enhanced response, will help us bring this under control,” an administration official said Sunday. “The military has unique capabilities in terms of logistical capacities, in terms of manpower, in terms of operating in austere environments.”

The administration faces formidable challenges in carrying out any response plan. Not only is the virus now spreading fast, but health workers and epidemiologists have been physically attacked or run out of villages by angry or frightened locals. Some locals argue that Ebola is a bioweapon seeded by the West.

Joanne Liu, international president of Doctors Without Borders, called earlier this month for governments to send in their militaries. The aid organization has led treatment efforts since the beginning of the Ebola outbreak and has been warning for months that a bigger response is needed.

“Without this deployment, we will never get the epidemic under control,” she said.

—Julian E. Barnes contributed to this article.

Write to Carol E. Lee at carol.lee@wsj.com and Betsy McKay at betsy.mckay@wsj.com