"This upcoming trip to the two summits is in many ways a continuation of the president's first trip to Europe in June of this year and the Sea Island summit," said a senior administration official.
The visits to Ireland and Turkey are "framed in the immediate sense by the international community beginning to come back together and reunite over a set of shared goals in Iraq," said the official who spoke on condition of anonymity.
Bush will meet in Dromoland late Friday with Irish Prime Minister Bertie Ahern, whose country will be holding the rotating presidency of the European Union until the end of the month.
European Commission president Romano Prodi will take part in these talks.
The last US-EU summit, held in June 2003 in Washington, was marked by serious tensions between the two sides caused by the war in Iraq that was launched in March 2003.
Europeans and Americans announced there the launch of negotiations on an "open skies" aviation accord.
But the talks proved more difficult than expected, and, contrary to earlier expectations, this agreement is not expected at the summit.
Dublin is seen as one of Washington's historic allies, and Ahern is believed to have a good relationship with Bush.
However, anti-American demonstrations were still expected in Irish capital, a rare sight there.
Conscious of negative emotions generated by his policies in Europe, the US president has already used his visits to Italy and France to launch a charm offensive.
The offensive aims primarily to generate support for Washington's strategy in Iraq, where the United States plan to transfer sovereignty to an interim government on June 30.
The issue will be at the center of discussions at the summit in Istanbul scheduled to take place there Monday and Tuesday.
However, before the NATO summit, Bush will have bilateral talks with Turkish leaders in Ankara, another historic US ally has refused to take part in the Iraq war.
Interim Iraqi Prime Minister Iyad Allawi asked Wednesday for NATO assistance in training his government's security forces, without asking for alliance troops.
Fifteen of 26 NATO members have troops in Iraq, but the alliance itself has so far limited its role to providing logistical assistance to a Polish-led international division.
Faced with resistance on the part of France and Germany, Bush discounted at the Group of Eight summit in Sea Island this month the possibility of more NATO troop deployments in Iraq.
"I don't expect more troops from NATO to be offered up. That's an unrealistic expectation," he told reporters. "Nobody is suggesting that. What we are suggesting is for NATO perhaps to help train."
Democrat John Kerry, who will face off with Bush during the November elections, is accusing the president of failing to generate more international support for Iraq and of increasing US isolation in the world by offering unilateral initiatives.