After lining up for hours outside the U.S. Capitol, thousands of Americans paid their last respects to former president Ronald Reagan tonight as his flag-draped casket lay in state in the building's historic Rotunda following a solemn funeral procession down Constitution Avenue.

Admitted to the Capitol after a ceremony attended by Reagan family members and U.S. and foreign dignitaries, members of the public filed quietly past the casket on the opening day of the nation's first state funeral in more than 30 years.

Reagan's body is to lie in state in the Capitol Rotunda until Friday morning, when it will be taken to the National Cathedral for a funeral service attended by what commentators predicted would be the largest gathering of world leaders in U.S. history. After that service, Reagan's body will be flown back to his home state of California for burial at his presidential library on a hilltop overlooking Simi Valley.

A horse-drawn caisson delivered Reagan's casket to the Capitol this evening in a cortege that was watched by thousands of mourners as it slowly made its way down Constitution Avenue. Millions more watched the procession on television.

The caisson was accompanied by a military honor guard and followed by the traditional riderless horse as it proceeded slowly from the Ellipse, in front of the White House. At the Capitol, dignitaries led by Vice President Cheney and including former first lady Nancy Reagan honored Reagan's memory in a ceremony featuring prayers, eulogies and songs by a military choir.

Sticking closely to a carefully choreographed procedure steeped in the traditions of the U.S. armed forces, the cortege arrived at the Capitol on schedule at 7 p.m. EDT. Military pallbearers then carried the heavy mahogany coffin up the stone steps on the west side of the building as a band played "The Battle Hymn of the Republic."

Under the Rotunda's ornate 180-foot-high ceiling, the honor guard placed the casket on a wooden platform, called a catafalque, that dates to the funeral of Abraham Lincoln.

It was the first time that a former president had lain in state in the Capitol Rotunda since Lyndon B. Johnson in 1973.

The House and Senate chaplains gave benedictions in front of the catafalque as Cheney, House Speaker J. Dennis Hastert (R-Ill.) and Senate President Pro Tempore Ted Stevens (R-Alaska) looked on. Cheney was standing in for President Bush, who was attending a Group of Eight summit meeting in Georgia. Bush plans to attend the national funeral service for Reagan on Friday at the National Cathedral, where he will give the eulogy.

In speeches in the Rotunda this evening, Cheney, Hastert and Stevens recalled the highlights of Reagan's life, hailing him as the president who ended the Cold War and ushered in a period of hope and prosperity.

"In this national vigil of mourning, we show how much America loved this good man and how much we will miss him," Cheney said. After decades of the Cold War, "it was the vision and the will of Ronald Reagan that gave hope to the oppressed, shamed the oppressors and ended an evil empire," he said. "My fellow Americans, here lies a graceful and gallant man."

After a military choir sang "America the Beautiful," Cheney, Hastert and Stevens placed wreaths in front of the catafalque. Nancy Reagan, 82, then walked up and rubbed her hands over the flag covering the casket. Reagan's adopted son, Michael Reagan, kissed the flag and saluted.

Among the estimated 800 dignitaries in the marble-floored Rotunda were lawmakers, federal officials, Supreme Court justices and members of the diplomatic corps.

Before the public was allowed in, national and world leaders past and present filed past the casket. Some touched the flag and bowed their heads in prayer. Others crossed themselves or saluted.

Former British prime minister Margaret Thatcher was there, escorted by Senate Majority Leader Bill Frist (R-Tenn.). Former Canadian prime minister Brian Mulrooney and his wife paid their respects, as did former vice president Dan Quayle, several former Reagan administration Cabinet members and a number of legislators.

As the casket arrived at the Capitol, a military band played "Hail to the Chief," and three howitzers fired a 21-gun salute. Nancy Reagan saluted the casket from the Capitol steps as she held the arm of Maj. Gen. Galen B. Jackman, the commander of the U.S. Army Military District of Washington.

Shortly before the procession's arrival at the Capitol, 21 Air Force jets roared low overhead in a flyover, with one group of the planes executing the traditional "missing man" formation.

The proceedings began earlier in the day in California, when the casket was borne in a solemn cortege from the Reagan presidential library in Simi Valley. There more than 100,000 people had paid their respects to the 40th president, who died Saturday after a 10-year battle with Alzheimer's disease.

A U.S. Air Force 747 carried Reagan's casket from California to Andrews Air Force base southeast of Washington. Looking frail and weary in a black dress, Nancy Reagan slowly descended the red-carpeted stairs from the plane.

A hearse then carried the casket to Constitution Avenue NW at the Ellipse by the White House. There it was ceremoniously placed on the black artillery caisson drawn by six matched horses from the 3rd U.S. Infantry Regiment, known as "The Old Guard," based at Fort Myer, Va.

The 86-year-old caisson then began rolling down Constitution Avenue toward the Capitol, followed by the black riderless horse with brown riding boots placed backwards in the stirrups and a sheathed sword at the horse's side. The boots, which belonged to Reagan, were used at the request of his widow.

The tradition evokes the commander's parting look at his troops, who march behind him. The empty saddle on the horse symbolizes that the commander will never ride again.

Soldiers wearing blue ceremonial uniforms rode on only three of the caisson's horses -- those on the left -- leaving the other three saddled but without riders in another military tradition.

Accompanying the caisson was an honor guard composed of members of all branches of the armed forces.

Following the caisson and the caparisoned, or riderless, horse were various military units and bands. Nancy Reagan rode the length of the mile-and-a-half-long route in a black limousine.

As the crowd waited for the cortege to begin within view of the White House, someone broke the silence with a shout of, "God Bless you, Nancy." The crowd broke into applause.

Waiting along the cortege route in hot and humid weather for the casket to pass, mourners held up pictures of the nation's 40th president and placards proclaiming their reverence for him.

At the Capitol, police ordered waiting mourners and journalists to evacuate the area shortly before Reagan's casket was due to arrive at Andrews, but gave an all-clear after a few minutes. U.S. authorities said the evacuation was ordered because of an unidentified aircraft that flew near the Capitol.

"I've never been so scared in my life," said RoseMarie Wortman of Sterling, Va. "I thought it was a bomb or dynamite."

A federal official said later that the plane was a Kentucky State Police aircraft bound for Reagan National Airport with its transponder turned off. It took a few minutes to determine that the plane was not a threat.

Among those awaiting the funeral procession was Arlene Black, 67, of Reston, Va., who came to the corner of Constitution Avenue and 7th Street NW this afternoon with her daughter and three young grandchildren.

"I thought the world of Ronald Reagan," Black said. "I think the world of Nancy. Bottom line, I'm American. To the core of my being." The grandchildren "won't remember much about this," she said. "But we'll talk to them about it someday."

Carmen Rondesko, 80, made the trip to the Capitol from Sayerville, N.J., as "my tribute to Reagan," she said as she sat on a lawn chair while waiting to get into the Rotunda. A long-time admirer of Reagan, she said she did not know what she would do when she saw his casket arriving at the Capitol.

""I would just like to stand there and salute him," she said softly, "but I don't think I can. I'm just happy that I'm here so I can pay tribute to him."

Security was tight on the Mall today as it was transformed for three days of ceremony during which the city, in large measure, will close down.

Federal employees were allowed to take unscheduled leave today, meaning the time off does not need prior approval. Most D.C. government employees were allowed to request liberal leave beginning at 2 p.m.

Mayor Anthony A. Williams announced that D.C. government offices and public schools will be closed Friday, along with federal offices, as the country salutes the president with a National Day of Mourning and his funeral at the Washington National Cathedral.

Staff writers Fred Barbash, Monte Reel, Jacqueline Salmon, Raymond Flandez, David Nakamura and Spencer S. Hsu contributed to this story.