President Barack Obama is to deliver the eulogy for Sen. Edward M. Kennedy Saturday, taking on the role to which the senator himself was so often called as the longtime patriarch of his famous political family.

The funeral was expected to draw mourners from across the political spectrum and all stations of life.

The Massachusetts Democrat, who died Tuesday at age 77 from brain cancer, was being sent off in high fashion Saturday with a Roman Catholic Mass presided over by no fewer than seven priests, 11 pallbearers and 29 honorary pallbearers.

Tenor Placido Domingo was to sing, accompanied by cellist Yo-Yo Ma.

Joining Obama and nearly 1,500 other invitees at Our Lady of Perpetual Help Basilica were former Presidents George W. Bush, Bill Clinton and Jimmy Carter, as well as 58 current members of the U.S. Senate, 21 former members and Supreme Court Justice Stephen Breyer, once an aide to Kennedy.

The day's somber mood was matched by the gloomy weather. Rain and unseasonable cold enveloped the area as tropical depression Danny moved up the East Coast.

White House aides were mostly mum about the eulogy the president would offer, but Obama was expected to focus on the impact Kennedy had on American life since first being elected in 1962.

"This will be a personal message from the president about Senator Kennedy's impact as a friend, legislator, mentor, colleague and family member on those around him and our entire nation," said White House Deputy Press Secretary Bill Burton.

His 47-year career spanned the assassinations of his brothers, President John F. Kennedy and Robert F. Kennedy; the civil rights era and Apollo moon landings; and battles over health, education and immigration; as well as the country's election of Obama, its first black president, who was only 18 months old when Kennedy took office.

Obama, dressed in a dark suit and overcoat, left his hotel early Saturday to walk in a drizzling rain across the street to the Fairmont Copley Plaza for a 10-minute private visit with Kennedy's widow, Vicki.

The hotel has been frequented by the Kennedys for generations, and the halls on one floor are lined with family pictures.

After the meeting, Obama, hands in pockets, ignored a shouted question about the contents of his eulogy.

A military honor guard has stood by Kennedy's casket since it arrived at his brother's presidential library Thursday. A rotation of friends, former staffers and others Kennedy touched — including the parents of a murdered lifeguard, the family of an Iraq war soldier and the widow of a Sept. 11 terror victim — has maintained a 24-hour vigil.

On Friday, Kennedy was remembered at a bipartisan memorial service whose speakers included Sens. John McCain and John Kerry, Vice President Joe Biden and Caroline Kennedy Schlossberg, JFK's daughter.

"Now Teddy has become a part of history," Schlossberg said, "and we are the ones who will have to do all the things he would have done, for us, for each other and for our country."

The invitation-only funeral audience of world leaders and commoners alike evoked the funerals for Kennedy's brothers. It was at RFK's rites in 1968 that the senator not only emerged as family patriarch, but also the person to deliver the final word on lives cut short.

He memorialized Robert Kennedy by saying, "My brother need not be idealized, or enlarged in death beyond what he was in life; to be remembered simply as a good and decent man, who saw wrong and tried to right it, saw suffering and tried to heal it, saw war and tried to stop it."

Following the service, Kennedy's body was being flown to Andrews Air Force Base, which also received JFK's body after his 1963 assassination, before being driven to the U.S. Capitol then along the National Mall and into Arlington Cemetery.

There, as evening falls, he was to be buried on a hillside grave site near his two brothers.