SINGAPORE - McLaren team principal Martin Whitmarsh has warned the United States will prove a much tougher nut to crack than Asia as Formula 1 prepares for its latest bid to win over the huge American market.The glitzy, Europe-based motorsport heads to Austin, Texas, in November and will add New Jersey to its schedule in 2013 after successfully establishing itself in the Asia-Pacific region with seven races this year.FIRST US F1 GP SINCE 2007Singapore's night race has been guaranteed for another five years until 2017 and India made its debut on a purpose-built track in 2011, joining Australia, Japan, Malaysia, China and South Korea on the Asian circuit.But Whitmarsh said F1 may find the going tougher in the United States, where the sport has a chequered history and will be competing with other motorsports. Austin will be America's first grand prix since 2007.Whitmarsh said during the Singapore GP weekend: "We've got to recognise that we've got to work harder at it than probably any market we've worked at."We go around parts of Asia, South America and Europe, one could plonk a grand prix down and there's a natural fanbase. It's been easy for us and I think we've taken it too easy."Whereas in America, they have lots of great sports they've got lots of entertainment opportunities other than F1."If we're going to go there and make a success of it we've really got to work hard on it and it'll take a few years to really catch on."McLaren drivers Jenson Button and Lewis Hamilton were both enthusiastic about the American races. Austin is known as a vibrant, young city, and New Jersey's race will have the Manhattan skyline as a spectacular backdrop.Hamilton said: "It's going to be great to go back to the States."It's obviously such an important market for F1 because there's so many people there that we need to turn to F1 to show them that it's better racing than some of the other racing that they're watching, or as good."HUMILTY REQUIREDBut Whitmarsh said F1 would have to take a more humble approach to overhaul America's home-grown IndyCar series, especially after incidents such as Indianapolis 2005, when most teams withdrew in a dispute over tyres."I think it's important to remember that America's important to us but America doesn't need us," Whitmarsh said. "We have to go there with the appropriate humility recognising that we haven't done the greatest job for F1 there in the past, for a host of reasons that we know of, from the tyre fiasco in Indianapolis and the venues we've been to, the inconsistency."I think we've got to go there now and have a proper five-year programme which is concentrating on getting people enthused about it."Button said Austin was a good place for F1 to attempt to get a foothold."Having it in Austin is great because it's a very young city and that's what we need, to get young fans into the sport," Button said. "That's the way to grow the sport in the US and hopefully we will do that."