"Our nation is shocked and saddened by the new of the shootings at Virginia Tech today," Bush said from the White House Diplomatic Reception Room.
The president said he and first lady Laura Bush are praying for the families of victims.
"We hold the victims in our hearts, we lift them up in our prayers and we ask a living God to comfort those who are suffering today," Bush said.
The shattered tranquility of one of America's bucolic higher education institutions left a devastating wake in the nation's capital, located four hours up the road from the Blacksvurg, Va., campus.
The shock reverberated north through the state capital of Richmond and to Washington, D.C., after news that at least 32 people died in Monday's shooting in two incidents on VT's campus. Two buildings — the Ambler Johnson West dormitory and the Norris Hill engineering building — were the sites of the mass murder that took place in waves two hours apart.
The Senate and House also held moments of silence as lawmakers started their workweek.
"Today our country has been struck by a terrible, terrible tragedy. ... This is the worst campus shooting in the history of our country," said Speaker Nancy Pelosi, D-Calif., who crossed herself on the House floor after the moment of silence. "(Republican) Leader (John) Boehner joins me in extending our condolences to everyone concerned."
Senate Majority Leader Harry Reid, D-Nev., said the shooting "breaks our hearts and shakes us to our very cores."
"We pray for those who were lost and for the speedy recovery of the wounded. And we pray that America can find the strength to overcome our grief and outrage as we face this tragedy together," he said.
Bush's spokeswoman Dana Perino said she made the president aware of the shootings at 12:35 p.m. EDT.
"He was horrified and his immediate reaction was one of deep concern for the families of the victims, the victims themselves, the students, the professors and all the people of Virginia who have dealt with this shocking incident. His thoughts and prayers are with them," Perino said. "We are monitoring the situation whereas state and local authorities are in the lead now and I think that will remain the case, but federal assets are available should they be needed, if Virginia were to request them."
Perino added that Bush and Education Secretary Margaret Spellings held a conference on school gun violence last October.
"The president believes that there is a right for people to bear arms, but that all laws must be followed. Certainly, bringing a gun into a school dormitory and shooting ... is against the law and something someone should be held accountable for," Perino said.
Attorney General Alberto Gonzales said, "Americans can rest assured that law enforcement resources" from the Department of Justice are assisting state and local authorities in the investigation.
"We are committed to providing support and assistance to those authorities as well as to the victims of this crime for as long as necessary," Gonzales said.
A senior official with the Bureau of Alcohol, Tobacco, Firearms and Explosives told FOX News that the ATF's response to the incident was "immediate," and the bureau is making all of its local and national resources, including its crimes lab, available to the Virginia State Police.
Ten ATF agents are now on the Virginia Tech campus assisting state and local police with weapons identification. They are collecting shell casings and running some preliminary tests on scene, and once the weapon has been identified they will begin an "urgent trace" to determine its origins — where it came from, to whom it was registered, and its history of ownership, the official said. All material will be sent to the ATF's national crime lab in Maryland.
The ATF is also assisting with "forensic mapping" of the crime scene — a painstaking process employed by investigators that 'maps out' the scene and incident in minute detail.
Hearing about the news, Virginia Gov. Tim Kaine, who was traveling to a meeting in Tokyo, Japan, on a two-week trade mission, was re-routed back to the United States. His office issued a statement saying that the state is working closely with Virginia Tech officials, local law enforcement and the community health system to provide resources and support.
“It is difficult to comprehend senseless violence on this scale. Our prayers are with the families and friends of these victims, and members of the extended Virginia Tech community," Kaine said. “I urge Virginians to keep these victims and their families in their thoughts and prayers.”
State Attorney General Bob McDonnell canceled his schedule for the next two days and planned to attend a memorial event on Tuesday in Blacksburg, Va., where the school is located.
"We pray for all those injured, that they will recover from their injuries. I urge my fellow Virginians to pray for all those impacted by this heartbreaking occurrence," McDonnell said in a statement.
Back in Washington, D.C., House Republican Conference Chairman Rep. Adam Putnam of Florida extended his "thoughts and prayers."
"This tragic day in Blacksburg will be burned into memory for a long time to come. From what we know so far, we have lost many bright young minds at the hands of a deranged individual who senselessly violated the sanctuary of the Virginia Tech campus," Putnam said.
Democratic Sen. Jim Webb, whose own staffer was arrested last month for accidentally carrying into a Senate office building a 9mm, the same type of gun believed to be used in the killings, said he was "truly saddened to hear of the tragic shooting" at the school.
"My heart goes out to the parents and families of the victims of this senseless act. My office has been in communication with the governor's office and officials at Virginia Tech to offer any assistance," Webb said.
The 2008 presidential candidates also began displaying their messages of condolences on their campaign Web sites.
FOX News' Ian McCaleb contributed to this report.