The White House is pledging a thorough investigation into the loss of the shuttle Columbia and it's seven astronauts, and vows the space program will continue. President Bush has scheduled a meeting with the head of the national space agency for later Monday, and plans to pay tribute to the seven shuttle crew members at a memorial service on Tuesday.

White House Spokesman Ari Fleischer makes clear, the president is taking a strong personal interest in the shuttle investigation.

He says, Mr. Bush has summoned NASA Director Sean O'Keefe to his office for a full briefing on the tragedy. The president has also instructed Mr. O'Keefe to go to Capitol Hill to answer questions from key members of the U.S. Congress.

Mr. Fleischer says President Bush will attend a memorial service for the astronauts on Tuesday at the Johnson Space Center in Texas, where they trained for their flight. He says the president continues to get condolance calls from foreign leaders, and spoke Sunday with the prime ministers of Pakistan, Spain, and India, where one of the astronauts was born and raised.

The White House spokesman stresses that the president wants to explore every possible way this tragedy could have happened. Mr. Fleischer said it will be independently reviewed and "no stone will be left unturned."

During a conference-call with reporters, Mr. Fleischer was asked if the ill-fated space mission might have an impact on plans to send Secretary of State Colin Powell to the U.N. Wednesday to provide evidence on Iraq and its suspected weapons of mass destruction. He said the president views the loss of the shuttle as a tragedy that has touched the lives of the American people, but does not see a connection to other events in the world. He added it will not have an impact on any of the president's responsibilities to keep the peace or protect the American people.

And yet, for the second time in his presidency, Mr. Bush finds himself playing not just the role of commander in chief. As he did after the September 11, 2001, terrorist attacks, he is leading the nation in mourning, and vowing to press on.

Some have wondered if, perhaps, this tragedy has had more of a personal impact on the president, as the shuttle disappeared over his home state of Texas. But his spokesman denies that is the case, saying that from the president's point of view, the debris may have landed in Texas and neighboring Louisiana, but its impact was felt around the world.