Four miles from the White House, Army specialists are digging very cautiously into an empty lot where a brick house once stood in one of the district’s toniest neighborhoods, on the edge of the American University campus.

A giant tent covers the site, alarms ready to sound if deadly poisons should leak. After decades of work, decontamination of the old burial ground for World War I chemical munitions is expected to be finished by late next year.

Next year, meanwhile, is also the deadline for Syria to eliminate its entire chemical arsenal, from one end of the country to another, under the American-Russian plan announced 10 days ago.

The disparity between the Syrian rush and the American slog underscores the difficulties facing that plan, even if Syria cooperates. Almost everything about the American effort to rid itself of chemical weapons manufactured from Woodrow Wilson’s presidency to Ronald Reagan’s has been more complex, more time-consuming, more costly and more environmentally fraught than anyone imagined.

The bill now stands at $35.4 billion, with no end in sight, for an epic of chemical destruction involving not just this Washington neighborhood of ambassadors and former presidents, but hundreds of sites nationwide, from a giant incinerator in Utah to a weapons dump in Alabama more than five miles long.

Of course, the American arsenal was much older than Syria’s, and some 30 times as large, when the United States in 1997 embraced the global treaty banning chemical arms. And unlike Syria, it has had to contend with citizen opposition to some decommissioning plans.

On the other hand, the United States has no civil war to get in the way of the dangerous work of dismantling chemical weapons.

But fundamentally, the disparity between the two plans centers on differing philosophies of chemical disarmament – quick and dirty versus slow and costly. Over the decades, the United States went from one approach to the other as concerns grew about possible threats to public health and the environment.

Chemical experts point to the possibility of a hybrid approach that would dispatch Syria’s arms relatively quickly while minimizing the risks.

"The technologies exist," said Lenny Siegel, the executive director of the Center for Public Environmental Oversight, a group in Mountain View, Calif., that has closely monitored the Army’s toxic cleanups. "The weapons can be destroyed safely — not real quickly, and definitely not cheaply. But it can be done."

The U.S. arsenal goes back to 1917, when the nation began producing mustard gas and other poisons for use in World War I.

Over the decades, the arsenal got much deadlier. A leading poison was sarin, the same gas used in the Aug. 21 attack in the suburbs of the Syrian capital that the Obama administration says killed more than 1,400 Syrians. It throws nerves and muscles into overdrive, resulting in convulsions, lung paralysis and death. Victims’ pupils are often tiny because the iris, a muscle, contracts so much.

As a rule, chemical weapons are easier to make than to destroy. "Everybody forgets that none of these weapons were designed to be peacefully disassembled," Miguel E. Monteverde, an Army spokesman, noted in an interview. "It was always assumed that they’d be used."

When the United States first began destroying leaky and obsolete munitions, it took the fast approach. It burned and buried them. In time, a forgotten dump became Spring Valley — the Washington neighborhood of elegant homes.

"We know we’re going to find things, but we’re not sure what," Andrea Takash, an Army spokeswoman, said Friday. The overall bill for the neighborhood’s cleanup, she noted, is expected to run to more than $230 million.

The next means of disposal was simply to dump munitions at sea. The United States did so until the early 1970s, when a global treaty outlawed such practices.

Finally (environmentalists would say belatedly), the Army turned to a costlier method. It built decommissioning plants in Alabama, Arkansas, Utah, Oregon and on a Pacific atoll. Special furnaces incinerated the poisons at extremely high temperatures and then scrubbed out dangerous waste products.

But citizens near the big facilities and at sites of proposed ones worried about accidents, toxic fumes and health risks.

In 1984, Craig Williams, a Vietnam veteran living in rural Kentucky, went to a public meeting about a planned incinerator. On his way home, he recalled, his wife said, "Craig, somebody’s got to do something about this."

Williams lobbied hard against incineration, organizing civic groups around the nation while battling Army brass and testifying before Congress. "We realized we couldn’t prevail by having a spaghetti dinner once a week," he said in an interview.

Slowly, the Army adopted what the citizens groups praised as a safer approach — neutralization, in which water and other chemicals react with the deadly chemicals to undo their toxic structures.

As the Cold War ended, so did the military’s production of chemical arms, and the elimination work sped up. Abolition went global in 1993 with a treaty known as the Chemical Weapons Convention. It went into force in 1997.

The Army built giant neutralization plants in Maryland and Indiana. Today, at a cost of $10.6 billion, it is erecting new ones near Pueblo, Colo., and Richmond, Ky. The Kentucky workforce now stands at more than 1,200 people, and the plant is set to destroy 523 tons of mustard gas and nerve agents, including sarin. The chemical destruction job is expected to be finished by 2023.

Beyond the arsenal and the nine decommissioning plants lurks a major cleanup dilemma – what, if anything, to do about the estimated 250 old dump sites for chemical arms that dot the nation. Unlike Spring Valley, most are on military bases or remote sites far from dense populations.

Last year, the National Research Council put out a lengthy report calling the old dump sites "a huge challenge." The cost of cleaning up just the five miles of weapon trenches in Alabama, it noted, is estimated at several billion dollars.

The report detailed scores of portable technologies — everything from air monitors and excavation gear to demolition trucks and detonation chambers — that already exist and could speed the domestic cleanup.

Siegel, of the Center for Public Environmental Oversight, noted that the mobile nature of the technologies meant they could play an important role in the rush for Syria’s chemical disarmament. The plan now calls for its completion by July.

"If you want to act quickly, the technical decisions have to be made now, while the diplomats are working," he said. "This is difficult stuff and it’s costly but the technologies exist — though most people don’t know that."

A better appreciation of the American experience and the available technology, Siegel added, would make it easier for diplomats and government officials to develop a strategy for the undoing the Syrian arsenal.

© 2013 The New York Times Company