Tens of thousands of federal employees in Philadelphia and South Jersey - including civilian members of the military - are to be furloughed Tuesday after the U.S. government plunged into a partial shut down ovenight.

Nine national parks in New Jersey are closed, while Independence Hall, the Liberty Bell, and Valley Forge will turn away visitors.

Furloughed workers at Independence Park, in the meantime, plan to hold an informational picket at the park at noon Tuesday.

But many critical services - from airport screening to customs inspections, health care for veterans to mail delivery, Coast Guard patrols to immigration processing - remain in place. Federal courts will stay open for at least 10 business days.

Private institutions, including the National Constitution Center, will be open.

The economic toll on the region will depend on the duration of a federal shutdown.

"A day or two or three or four is no big deal," Mark Zandi, chief economist with Moody's Analytics in West Chester, said Monday. "But we get beyond that and we have a big problem."

Zandi noted that the threat to the economy will rise every day and begin to really matter around Oct. 17, when the nation hits its debt limit. As November approaches, the economic effect could be cataclysmic. That's when the nation will enter uncharted waters pertaining to paying Social Security and interest on its bonds, he said.

There are 46,880 federal employees in the Philadelphia and Camden metropolitan areas, according to the federal Bureau of Labor Statistics. This is between 1.5 percent and 2 percent of the region's workforce.

In Philadelphia, tourism would be hardest hit.

The 186 employees of Independence National Historical Park are to be furloughed, with just a staff of law enforcement officers staying on to secure the 54-acre property, Jane Cowley, public affairs officer for the park, said Monday.

In all, 12 buildings will be shuttered, potentially keeping out 10,000 visitors a day, the average in October 2012.

The region could take a substantial hit if the park closes: In 2011, 3.5 million visitors to the park spent nearly $150 million in the region, supporting more than 2,000 jobs, according to a National Park Service report.

In 2012, visitor spending in the five-county region generated $9.75 billion, supporting 89,000 full-time jobs, according to the Greater Philadelphia Tourism Marketing Corp.

At Valley Forge National Historical Park, which sees about 4,000 visitors a day in October, employees were told to watch the news and not come to work in the event of a shutdown, superintendent Kate Hammond said Monday.

Most of the approximately 55 staff members, including Hammond, are to be furloughed, except for about 10 law enforcement officers whose duties are considered essential.

While a few state roads that run though the sprawling site would remain open, all of the trails and buildings would be gated or locked up and all scheduled tours, class visits, and programs would be canceled, Hammond said.

At the vast Joint Base McGuire-Dix-Lakehurst in New Jersey, where 44,000 people live and work, about 6,700 civilian workers for the Department of Defense are affected. Military personnel, however, are not subject to furlough.

"We're working to see who will be furloughed and who will not," base spokeswoman Angel Lopez said Monday.

She said informal notices went out last week to those who might be affected. Formal notices would be sent by letter. Some civilian employees, in jobs such as transportation support for troops, may be required to remain for national security reasons, officials said.

In the event of a shutdown, the base would have town hall-style meetings, one for the Dix and McGuire portion, and another for the Lakehurst side of the base.

"We're planning for a worst-case scenario," Lopez said. "We'll stop operations for all activities that are not essential."

The shutdown also will affect the New Jersey National Guard, said Army Chief Warrant Officer Patrick Daugherty, a guard spokesman.

At least 950 other civilian employees could be sent home, Daugherty said.

"Everyone will show up for work [Tuesday], and will be there for a minimum of four hours," he said.

If a shutdown does not end quickly, the regular monthly training of Guard members set for October will be canceled, Daugherty said.

The closing of the federal government, however, will not affect New Jersey's veterans nursing homes in Vineland, Paramus, and Menlo Park, Daugherty said. Their funding is provided through the New Jersey Department of Military and Veterans Affairs.

In West Philadelphia, the VA Medical Center will remain open. Counseling services for military sexual trauma, readjustment, and other crisis issues will continue, and the national call center and crisis hotline will be staffed.

However, some services, such as an education hotline for the Veterans Benefits Administration and the processing of job applications, will halt.

Immigrant services are not affected by a federal shutdown. Citizenship and Immigration Services, which recently moved to 30 N. 41st St. in West Philadelphia, derives most of its budget from fees for visas, naturalizations, and other services, and not from annual federal appropriations.

At Philadelphia International Airport, airline services are not affected. Officers for the Transportation Security Administration (TSA) will continue to screen passengers and air traffic controllers remain on the job.

U.S. Customs and Border Protection officers will continue screening flights arriving from outside the United States and inspecting ships arriving at ports, including Philadelphia. The Coast Guard, meanwhile, will continue to monitor waterways around Philadelphia, including the Delaware.

The last time the federal government came to a halt was in 1996, when a seven-month budget battle in Congress resulted in two partial shutdowns.

In Philadelphia, tourist-industry experts were beginning to mull the impact of a government shutdown.

"No one is happy about having to turn away visitors," Crowley, the park's public affairs officer, said.

During the fall, schoolchildren from the region make up a large percentage of visitors, she said.

To counteract a potential closure of the park, the Greater Philadelphia Tourism Marketing Corp. will be "going overboard promoting everything that isn't shut down," said Meryl Levitz, president and CEO.

"The danger is people thinking there's nothing in Philadelphia that's open if the park is closed," she said. "We will put forth a mighty effort in the media and on social media."

In October alone, she said, more than 50 special events and festivals are scheduled in the city. On Independence Mall, meanwhile, the nonprofit, private National Constitution Center will remain open.

On Monday, Benny and Tommie Ingram, a couple from Georgia on a two-month road trip that included stops at national parks and historic sites, were riding their bikes through Valley Forge Park. They planned to visit Gettysburg next, but said they would have to cut short their trip and return home if the government shuts down.

"We've never been to Gettysburg. We've been really looking forward to it, and we hope something is done," Benny Ingram said. "At the same time, we would love to see the country get its budget under control. But, selfishly, not at our expense."

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