An uncontrollable, deadly virus ravages America, shutting down civilian institutions and triggering martial law. Vaccinations are compulsory, and there are mass quarantines throughout the country.

It's the stuff of Hollywood — but rumors that it could be real are spreading like the flu in the blogosphere, where some people are loudly expressing their fears that the federal government is seriously considering such measures as it maps out a worst-case-scenario response to the swine flu pandemic.

During the bird flu scare of 2005, the Bush administration added novel forms of influenza — including the swine flu — to the official list of "quarantinable communicable diseases," clearing the way for the forced detention of people who exhibit symptoms of the disease.

Now a proposal awaiting Defense Secretary Robert Gates' approval would allow the military to set up regional teams to assist civilian authorities in dealing with the impact of the swine flu pandemic. And some observers see this level of government preparedness as little more than a pretext for tyranny.

"The implications are far reaching," Michel Chossudovsky wrote on the Global Research Web site, which averages 18,000 visitors daily. "The decision points toward the establishment of a police state," he said.

"It would be extremely troubling and raise serious constitutional questions," Chris Calabre, ACLU counsel for technology and liberty, told FOXNews.com when asked how the civil liberties group would react to mandatory quarantines. "We opposed this in 2005 and will do so again because it gives the government blanket authority to hold anyone and has no due process."

Foreign governments, too, are thought to be drawing up worst-case emergency plans that rely heavily on armed forces.

"In addition to planning mass graves and crematoriums operating around the clock, governments are planning to implement martial law in response to a pandemic," Kurt Nimmo wrote on Infowars.com, which has been tracking disturbing developments in swine flu preparedness.

Nimmo pointed to a report in the Daily Telegraph that referred to the British government's emergency plans for "mass graves, inflatable mortuaries, 24-hour cremations and 'express' funerals."

Simon Barrett, press officer with the Home Office Press Office, referred questions about Britain's plans to a 2004 Department of Health publication titled, "Pandemic Flu: a national framework for responding to an influenza pandemic," which makes no mention of mass graves and rapid body disposal.

"Whilst there may be an increase in the number of flu-related deaths, local authorities will be able to cope using normal practices," Barrett said.

Britain's planning document makes no mention of martial law, but stresses the need to maintain operational readiness.

"Plans should not assume that local military units would provide support or have personnel available with either the requisite skills or equipment to perform specialist tasks," according to the document.

But — even if such severe measures were in the planning stage — would they amount to hysteria? Or would they be prudent precautions? Many point to the Spanish Flu pandemic of 1918, which killed between 20 million and 50 million people worldwide. Extrapolating those numbers to today's population suggests a comparable death toll of 360 million people, according to Michael Osterholm of the University of Minnesota's Center for Infectious Disease Research & Policy.

"Expect nothing to happen and prepare for the worst, " says Dr. Peter Katona, an infectious disease expert at UCLA. "We will need ample supply of vaccine and a distribution system that prioritizes who gets it and when." But, he added, "we won't need the military unless it becomes really bad, and the National Guard will be called in first."

Defense Department spokeswoman Almarah Belk acknowledged the rumors, saying, "There is a camp of people out there concerned about civil liberties and the use of force."

But she said the planning at the Pentagon is in response to a request from the Department of Homeland Security, and it primarily involves logistics like airlift capabilities for patient transport or delivery of medical supplies.

Except in special circumstances, the military is forbidden from enforcing civilian law under the Posse Comitatus Act, a Civil War-era law that ended the use of federal troops to oversee elections in former Confederate states.

"There are checks and balances in place that prevent the use of the military to restrict people's movement or go house to house," said attorney Robert L. Shannon, Jr., an expert on legal restraints covering the military in civilian affairs.

"But it's important to remember that the president has the option and authority to use federal troops in a national emergency," he added. " I think if we do have a doomsday scenario with swine flu, the American people are going to want their government to respond."

Shannon, who is vice commander of the Georgia Air National Guard, has firsthand experience from deployments during Hurricane Katrina.

"If we learned anything from that experience," he said, "it's that thorough advance planning for worst-case scenarios is essential, especially when you've got to coordinate so many different state and federal agencies."

Forced quarantines were common in the era before vaccines, but health experts doubt their effectiveness and practicality in fighting swine flu.

"This doesn't appear to be an especially deadly strain," said Deborah Lehman, Director of Pediatric Infectious Disease at Cedars Sinai hospital in Los Angeles. "At this point it looks like the seasonal flu will be responsible for more deaths than swine flu.

Many experts privately worry not about an overwhelming government response — but about an inadequate one. "There's simply not going to be enough vaccination doses to go around," said one pharmaceutical industry executive who declined to be named.

"You're more likely to see the military protecting health facilities and hospitals instead of forcing people to get medication," the executive said.

So rewrite the script: An uncontrollable, deadly virus ravages the population, triggering martial law to protect a handful of survivors lucky enough to get a vaccination.