Merkel rolled up to the South Portico of the White House in a limousine, and was welcomed by US President Barack Obama and his wife Michelle before a 19-gun military salute and the playing of the German and American national anthems.
The chancellor, in a lime green jacket and black trousers, reviewed an honour guard with Obama before greeting a line of cheering schoolchildren waving American and German flags on the South Lawn of the White House.
"Germany at the heart of Europe is one of our strongest allies and Chancellor Merkel is one of my closest global partners," Obama said in welcoming remarks. "Our alliances with nations like Germany are more important than ever, indeed they are indispensable."
Merkel said she was overwhelmed by the "very moving" and warm welcome.
"We Germans know that America has always been a true friend to us, our friendship has grown and matured... and every day it is filled with new life," she said.
"In Berlin in 2008, you spoke to more than 200,000 people. And in your address, you said America has no better partner than Europe. And now it's my turn to say Europe and Germany have no better partner than America."
Obama greeted Merkel privately on Monday night and took her out to a private dinner in the upscale Georgetown neighborhood of Washington, and is rolling out all the pageantry the United States can muster.
At a lavish state dinner later Tuesday, he will also present Merkel with the US Presidential Medal of Freedom, another rare honor which seems to designed to scotch persistent reports in Europe that despite mutual respect, there is little personal warmth between the leaders.
The visit also comes two weeks after Obama's visit to Europe, in which he billed the transatlantic alliance as the cornerstone of US foreign policy, despite perceptions that he is more concerned about rising India and China.
Merkel is in Washington at a moment of high sensitivity for her government, as Germany fights a deadly E. coli outbreak that has prompted US officials to inspect all imports of cucumbers, lettuce and tomatoes from Germany and Spain.
The talks between the two leaders in the Oval Office focused on the crises in North Africa and the Middle East, eurozone financial turmoil and other key issues.
Germany caused frowns in Washington by abstaining in a UN Security Council vote that endorsed NATO action against Muammar Qaddafi's forces in Libya. Germany, which has a non-permanent seat on the council, was the only European Union or NATO member to withhold its support.
But after speaking with Obama, Merkel underlined that Germany was "committed to the Libyan cause" and the success of the NATO mission.
Merkel said through a translator that "Qaddafi needs to step down, and he will step down," adding that Germany was taking part in the mission as a NATO member and stepping up its contribution in the Afghanistan war.
"It is a jointly held intention that this NATO mission is successful," Merkel said. "It's important for the people in Libya, but it's also important for NATO, for the alliance at large, and here we have one heart that beats with the allies."
Trying to smooth over the differences between the two sides over Libya, Obama praised Germany for taking on additional responsibilities in the Afghanistan that have "freed up resources" for the war in Libya.
"The chancellor and I have been clear. Qaddafi must step down and hand power to the Libyan people, and the pressure will only continue to increase until he does," Obama, standing alongside Merkel, told White House reporters.