White House spokesman Scott McClellan said plans for a European Union defence cell were among a "a range of issues" discussed by the two leaders.
Bush insisted the United States seeks "a dynamic, mutually reinforcing relationship between NATO and the EU, without duplication and divisiveness, and grounded in the essential NATO-EU agreements which underpin it," McClellan told reporters.
Blair has supported plans to strengthen European cooperation on defence and a greater role for Europe's rapid-reaction force within UN operations. This has reportedly caused tensions with Washington.
But the US president highlighted a joint US-British statement released when Bush visited Britain two weeks ago.
The United States fears that an EU defence initiative would rob the North Atlantic Treaty Organisation of some military capability and "double up" existing military structures.
The London statement maintained US and British support for a European security and defense policy that "improves Europe's capabilities to act and develops in a way that is fully coordinated, compatible and transparent with
It also stressed that, "with new members and new capabilities, NATO will be a cornerstone of world security in the 21st century."
The same US warning over a European defence initiative was made by US Secretary of State Colin Powell in a speech to NATO foreign ministers in Brussels.
Powell said: "The United States cannot accept independent EU structures that duplicate existing NATO capabilities."
The row over Europe's defense initiative has been simmering for months, ever since four countries opposed to the Iraq war -- France, Germany, Belgium and Luxembourg -- unveiled plans in April for an autonomous military planning cell outside Brussels.
The United States at one stage warned that the plans represented a "significant" threat to NATO, which has long been dominated by the United States.
The British prime minister has insisted that European defence can be improved without undermining NATO.
"There is nobody I know of in Europe that wants to see European defence go forward at the expense of NATO," Blair told a November 27 press conference with President Jacques Chirac of France.
"NATO will remain the cornerstone of our defence," Blair said.
"Neither the Germans nor the French wish in the slightest way to take any initiative which will be in contradiction with NATO, which as the prime minister has said, is the mainstay of European defence," Chirac said.
NATO leaders at the Brussels meeting expressed confidence Thursday that the European Union will not duplicate Alliance structures with its own military planning cell.
"The principle of non-duplication and absolute complementarity are shared by everyone," said Italian Foreign Minister Franco Frattini, whose country currently holds the EU presidency.
Speaking at a joint press conference with NATO chief George Robertson, the Frattini added: "I am not in favour of any planning process that will be duplicative of NATO structures."
Robertson added: "Together we will find a solution .. that will avoid unnecessary duplication .. but at the same time (which will) improve our military capabilities."