Aug. 4, 2010 -- A U.S. senator wants to know why more than 100,000 servicemen and women never received thousands of dollars they are owed by the Pentagon after being forced to extend their military tours during the height of the wars in Iraq and Afghanistan.

Sen. Frank Lautenberg, D-N.J., wrote to the Pentagon Tuesday wanting to know what the military has done to alert the service members that they are eligible for the money. As many as 145,000 men and women, most of them from the Army, were subjected to involuntary extensions of their military obligations starting in 2001 because the Pentagon imposed "stop loss" orders.

Lautenberg initiated legislation that required the Pentagon provide extra compensation to stop-lossed service members. A bill eventually passed last year.

But in the nine months since the special one-year, retroactive, stop-loss compensation program went into effect in October 2009, less than 20 percent of the eligible service members have received the pay, according to Lautenberg, citing Department of Defense figures.

The average amount owed each soldier or service member is between $3,000 and $4,000, according to the Stars and Stripes newspaper which first reported the stop-loss pay lag last month.

"I am concerned that more than 100,000 service members who qualify for these payments may never receive them," Lautenberg said in a letter to Defense Secretary Robert Gates. In the letter, a copy of which was obtained by ABCNews.com, Lautenberg requested detailed information on the Department of Defense's efforts to reach those who are owed stop-loss pay.

Under the program, service members from all military branches who were individually stop-lossed -- and not part of an entire unit stop-lossed -- between September 2001 and September 2008 can claim $500 for every month they were kept beyond the end of their term of service.

The retroactive compensation program, created by Congress via the War Supplemental Appropriations Act of 2009, and funded with more than $500 million, ends on Oct. 21.

Around 50,000 total claims have been filed, many of them coming in the past few weeks, according to the Army.

Armed forces members stop-lossed after September 2008 are automatically given the extra pay.

"It's been difficult to track many of these individuals down," said Major Roy Whitley, project manager for the Army's special retroactive stop-loss pay program. "We're talking about a group of young individuals who are finished with their military service and who tend to move around a lot."

"Who knows for sure why more of them have not put in for it, but we're certainly doing everything we can," Whitley said.

More Than 100,000 War Veterans Owed Stop-Loss Pay

Joe Davis, a spokesman for the Veterans of Foreign Wars, said he is not buying the notion that the military is doing everything it can. "This is the U.S. military we're talking about. If they wanted to find these guys, they'd find them. They just haven't done a good job of putting the word out."

Whitley strongly countered this assertion, saying the Army has done a series of special mailings and set up a Facebook page.

Army veteran Ivan Stephens, 28, said he heard about the stop-loss back pay program right away, as soon as it began last year. So did many of his friends at Fort Hood in Texas where he finished up his active duty.

"Guys knew about it when it was being first proposed," he said. "I find it hard to believe that any vets owed money would somehow not know about this program."

Stephens, who served in Afghanistan in 2001 and Iraq from 2003-2004, was stop-lossed for eight months between June 2005 and February 2006. His initial retroactive pay claim was denied due to a technicality. Stephens, mildly frustrated but accustomed to Army red tape, continues to pursue his claim.

"I think the Army does have a tough time keeping up with current addresses," he said. "I know in my case they were sending mail to an old address. It's a bureaucracy."

For the Pentagon to continue collecting claims after the October deadline, Congress would have to change the law.

"I recognize that the Department of Defense has faced many challenges in reaching the eligible population and educating them on the application process," Lautenberg wrote. "But the Department should use every available outlet to locate these service members."