The agency will handle creative work for an advertising, marketing and PR initiative, which will begin in the UK and be backed by an initial $6 million budget.
It will work on the initiative in tandem with Edelman, the PR company, and BVK, a US-based integrated marketing specialist. Walker Media will handle UK media planning and buying.
The appointment, made after a pitch to senior officials of the US Department of Commerce two months ago, is the precursor to a TV and print campaign that will break later this year. M&C Saatchi in London will lead the campaign, but will work closely with its office in Los Angeles.
The advertising will aim to restore the fortunes of a US tourism industry that has been badly affected by the 2001 attacks on New York and Washington.
Foreign visitors spent $102 billion in 2000 but the figure dropped to $87.4 billion in 2002.
The campaign is intended not only to increase visitor numbers but also to increase the amount that they spend. It will also aim to make the US top-of-mind when people plan their holidays.
Moray MacLennan, the chief executive of M&C Saatchi, commented: "It's a fascinating assignment."