President Bush will celebrate St Patrick's Day in Chicago, joining the city's parade from the reviewing stands.
"It is a historic St Patrick's Day parade, and it provides him with a good opportunity to highlight and celebrate with the people of Chicago the contributions of Irish-Americans," the White House spokesman, Mr Scott Stanzel, said.
Observers also note that Chicago's large Irish-American population is likely to be a factor in Tuesday's elections, where several Republicans are facing tough races.
The centrepiece of the celebrations in the US will be in New York City, where the President, Mrs McAleese, will be among those attending the parade.
Also attending will be Senator Hillary Clinton. The parade is being dedicated to the police, firefighters and emergency service workers, many of them Irish-Americans, who died in the September 11th attacks.
Celebrations are also planned in Boston, San Francisco and Savannah, Georgia, which has a large Irish-American population.
The first official celebration of St Patrick's Day in London, marking the contribution of generations of Irish to the city's social, economic and cultural life, will take place in Trafalgar Square tomorrow.
The Mayor of London, Mr Ken Livingstone, will officially open the four-hour parade and festival, which, he hopes, will one day rival celebrations in New York and Dublin.
After a service at Westminster Cathedral, the official parade of Irish community organisations and entertainers will move through Victoria and Westminster, arriving at Trafalgar Square at about 2.30 p.m.
• Queen Elizabeth has sent the following message to the President: "It gives me great pleasure on the occasion of Ireland's National Day to extend to you and the people of your country my warmest greetings and every good wish for a peaceful and prosperous future."
This is the second time the queen has sent a St Patrick's Day message, reflecting the growing closeness and warmth of relations between Ireland and the United Kingdom, according to diplomatic sources.