European Union plans to boost its military capability, which have sparked Nato anxiety, will be discussed by the two sides on Tuesday.
France and Germany want separate military HQ for the EU
A special meeting on Monday was said by officials to have cleared the air.
Tuesday's talks, at a scheduled meeting of ambassadors, are expected to return to the subject.
The US has expressed fears that plans for EU military capability, including a Franco-German proposal for a separate military headquarters, are a serious threat to Nato.
US officials fear enhancing the EU's role will undermine Nato's position.
UK Prime Minister Tony Blair is trying to steer a tricky middle course, says the BBC's Stephen Sackur in Brussels, by refusing to accept the most ambitious Franco-German plans while accepting that the EU can and should develop an independent military capability to complement Nato.
The matter has come to a head now because European leaders are trying to agree on a constitution for the EU including a definition of the EU's defence commitments.
A meeting last week is believed to have degenerated into angry exchanges.
US ambassador Nick Burns demanded meeting
Monday's private meeting of Nato ambassadors was said to have been more constructive, and officials insisted there was no crisis.
"The atmosphere was much better," said a senior diplomat.
"The worst situation we could be in, frankly, would be if either side said we don't want to talk about this. So don't
belittle the ability of talk to be a therapy in its own way."
Nato spokesman Jamie Shea, who described the atmosphere as very good, said: "We all agreed that nobody is trying to harm Nato."
The meeting was called by the American ambassador to Nato, Nick Burns, who last week described the Franco-German headquarters plan as "the greatest threat to the future" of the alliance.
Nato's own operations are changing
But the BBC's Oana Lungescu in Brussels says there is still deep concern about the HQ plans and about a mutual defence clause in the draft constitution.
If a country is attacked, one senior official asked, who should it go to for protection - Nato or the EU? Britain, Poland and many others in Europe don't really think they need that choice, she says.