The cost of the new Capitol Visitor Center (search) could run as high as $559 million, more than double the estimated cost when the construction project broke ground in 2000.

The Government Accountability Office (search), the investigative office of Congress, also predicted in an analysis that the opening for the three-floor underground facility, originally scheduled for the end of 2005, would be further delayed. It said current plans to open in the summer of 2006 were optimistic.

The GAO analysis is the latest of several assessments to drive up the price tag of what is the most ambitious and expensive construction project in the history of the Capitol -- larger than the addition of the House and Senate wings in the 1850s.

In concluding that the real costs could be as much as $100 million above the $454 million currently budgeted, the analysis cited management problems for the project, which is being overseen by the architect of the Capitol, and low bid estimates.

Jennifer Hing, spokeswoman for Rep. Jack Kingston, R-Ga., who heads the Appropriations subcommittee responsible for the project's budget, said both Kingston and Rep. Jim Moran, D-Va., the top Democrat on the panel, "are very concerned" about the latest analysis "and plan to take a long hard look at it."

She said they plan hearings on the cost overruns and delays when the new Congress convenes next year.

The original project envisions a three-story underground facility on the east front of the Capitol where tourists could go through security and visit informational galleries before entering the Capitol building. It is to have a great hall where visitors can look up on the Capitol Dome (search) through skylights, a dining area with a capacity for 600, exhibition galleries, two theaters and gift shops.

Since the project began, $70 million has been added for underground House and Senate office space, $38.5 million for security after Sept. 11, and $48 million to pay for weather-related and other delays and higher-than-expected bids. A filtration system that was added will cost another $33 million.

The GAO recommended that Congress quickly address the funding gap of $60.7 million for what it considered to be specific cost overruns and set up a reserve account of $43.5 million to take care of risks and uncertainties that could drive the total additional cost above $100 million.