SEOUL - The US government shutdown will undermine American credibility abroad and lead allies to question its commitment to treaty obligations, the US defense chief warned on Tuesday as he prepared to put 400,000 civilian workers on unpaid leave.Defense Secretary Chuck Hagel, who was visiting South Korea to celebrate the two nations' 60-year-old mutual defense treaty, said Pentagon lawyers were analyzing a new law passed by Congress to see if additional civilian workers could be spared unpaid leave.But for the moment, when the department's 800,000 civilians report to work on Tuesday, approximately half will be told they are not exempted by law from the government shutdown and asked to go home, Hagel told reporters.The Pentagon and other US government agencies began to implement shutdown plans on Tuesday after Congress failed to reach a deal to fund the federal government in the new fiscal year beginning Oct. 1.A last-minute measure passed by Congress and signed by President Barack Obama will ensure the Pentagon's 1.4 million military employees worldwide will continue to receive paychecks during the shutdown. They were required to work under prior law but would not have been paid until Congress approved funding.The new law also ensures that civilians who are required to work despite the shutdown will also be paid, Hagel said. But under law, anyone not directly involved in protecting lives and property are not considered exempt and must be placed on leave."Our lawyers are now looking through the (new) law that the president signed ... to see if there's any margin here or widening in the interpretation of the law regarding exempt versus non-exempt civilians," Hagel said. "Our lawyers believe that maybe we can expand the exempt status."