WASHINGTON — Hundreds of visitors got their first look at the Capitol Visitor Center — an underground museum and now the first stop for people touring Congress — as it opened yesterday, three years late and $360 million over budget.

A 186-foot marble wall holds display cases that document the nation's milestones and key decisions in Congress. Visitors will find President John F. Kennedy's 1961 speech calling for the nation to send a man to the moon, Thomas Jefferson's 1803 letter urging Congress to fund the Lewis and Clark Expedition and James Madison's notes for the Constitution.

"It provides a splendidly presented civics lesson," said James Billington, the librarian of Congress. The new structure, he said, "will make the Capitol, the icon of our republic, more accessible to all of us than ever before."

At a dedication ceremony for the three-story underground center, House Speaker Nancy Pelosi said work has never ceased on the Capitol, "one of the most recognizable structures in the world," since construction began in 1793. She praised the inclusive nature of the center's main space, called Emancipation Hall in part because slaves helped build the Capitol.

A towering Statue of Freedom, the plaster model for the bronze sculpture that sits atop the Capitol Dome, dominates the visitor center's main hall.

The cost ballooned to $621 million, more than double the $265 million estimated cost if the center had been completed on schedule by December 2005.

Ground was broken in 2000 and the project was expanded after the 9/11 terrorist attacks to improve Capitol security.

The new center's marble corridors can accommodate thousands of people. It has two orientation theaters where people touring Congress can first view a film entitled "Out of Many, One," a 530-seat restaurant, 16,500 square feet of exhibit space, and 26 restrooms. Advance reservations, which can be booked online for free, are recommended for tours.