WASHINGTON -- Democrats in the U.S. Congress are stepping up scrutiny of the U.S. missile defense program in a sign that they are looking to pare down the billions of dollars that the White House has spent or plans to spend on building a defense shield.

The Democrats are raising questions about the effectiveness of the anti-missile program, which is bitterly opposed by Russia, and investigating whether its testing regimen is realistic enough to demonstrate the shield's capabilities against real missile attacks.

The scrutiny comes as the United States is at a sensitive moment in negotiations with Poland and the Czech Republic to build part of its shield on their territory. Lawmakers are questioning the security value of those plans against stark opposition from Russia

Congressman John Tierney is investigating the program's capabilities and costs and plans three to five hearings, beginning Wednesday.