Defense Secretary Robert M. Gates arrived on an unannounced visit to Afghanistan on Monday morning to meet with President Hamid Karzai and NATO commanders, and to review plans for a major American-led offensive into the Taliban heartland of Kandahar.  Mr. Gates gave no date for the anticipated push into the city of Kandahar, which has a population of 900,000 and is the capital of Kandahar Province in southern Afghanistan, but he said, “There is some very hard fighting, very hard days ahead.” Administration officials have said only that the campaign, a central mission for the 30,000 extra forces that President Obama has ordered to Afghanistan, will occur sometime this year.  Mr. Gates spoke to reporters on his plane en route to Kabul.  Gen. Stanley A. McChrystal, the top NATO and American commander in Afghanistan, later told reporters in Kabul that the offensive in Kandahar would be different from the recent American-led campaign to largely rout the Taliban from Marja, a much smaller town in Helmand Province. While the Marja offensive began with a burst of forces into the area in the middle of the night, General McChrystal said the Kandahar offensive would unfold more slowly. – New York Times