By David Alexander and Steve Holland

WASHINGTON (Reuters) - President Barack Obama on Tuesday appeared to back more rigorous procedures for dealing with soldiers returning from missions to Ebola-hit West African countries, even as he criticized moves by some U.S. states to quarantine returning civilian health workers.

Obama said that American military personnel were in a "different situation" compared with healthcare workers. While civilians may be discouraged from volunteering to help fight the Ebola if they are facing quarantine on their return, troops were sent as part of their mission and could expect such inconveniences.

"They are already by definition if they are in the military under more circumscribed conditions," Obama told reporters at the White House. "We don't expect to have similar rules for our military as we do for civilians."

The differences in approach played into a fierce debate in the United States over how best to treat Americans who may have come into contact with the disease when they came home from one of the three West African countries hit by Ebola: Liberia, Sierra Leone or Guinea.

The Pentagon said on Monday that Major General Darryl Williams, commander of U.S. Army Africa, and 11 of his staff were put in isolation for 21 days of monitoring after returning from West Africa to their home base in Vicenza in northeastern Italy.

The Army chief of staff, General Ray Odierno, ordered the isolation not because of medical necessity but to reassure troops and local communities that the Army was taking "all steps necessary to protect their health," an Army statement said.

Odierno's decision went beyond Pentagon policy, which calls for monitoring but not isolation.

The Obama administration has been seeking to dissuade U.S. states from imposing quarantines on doctors, nurses and other health workers returning from West Africa and has resisted political pressure to impose travel bans on people coming from the affected area.

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EBOLA ISOLATION PROGRAM

Obama's spokesman, Josh Earnest, said an isolation program was appropriate for the hundreds of military personnel returning to bases across the world while a self-monitoring program was right for the smaller number of returning healthcare workers.

Top U.S. military commanders formally recommended to Defense Secretary Chuck Hagel on Tuesday that the Pentagon impose a "quarantine-like" 21-day monitoring period on all U.S. military personnel returning from Ebola response efforts in West Africa.

Rear Admiral John Kirby, the Pentagon press secretary, said Hagel was considering the proposal, which would extend to all U.S. military personnel the kind of program imposed on Williams and his men when they left Liberia last weekend.

Kirby said Hagel was weighing a number of factors as he considered whether to approve the tougher monitoring, including the effect it could have on other agencies by raising fears about whether the government was acting appropriately.

"The spillover effect (of any decision) on other agencies and the American people certainly are on his mind. But his primary responsibility is to take care of the Defense Department, our troops and our families, and that’s always been foremost in his mind," Kirby said.

Dr. Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention, said most returning medical workers should have daily monitoring but did not need to be isolated. He called for voluntary home quarantine for those at greatest risk.

Kirby said Hagel supported the Army's decision to place Major General Williams and his team in isolation but was still deciding what to do about the return of future military personnel.

Unlike civilian medical workers, the U.S. military personnel sent to West Africa are not coming into contact with Ebola patients but are building facilities, including Ebola treatment units.

(Reporting by David Alexander, Phil Stewart and Steven Holland; Editing by David Storey and Jonathan Oatis)