The estimated completiondate of the Capitol Visitor Center has been officially been pushed back two months, and more delays are possible as the overdue, over-budget project continues to face critical challenges, the federal government’s chief watchdog said this week.

Contractors made progress on the 580,000-square-foot underground facility between March 13 and Tuesday, when the Government Accountability Office offered its most-recent update to Congress. But continued delays on the fire-protection system will push the scheduled completion — not opening — date to at least mid-2008 and perhaps later.