FALLOUJA, Iraq — Thousands of Marines surrounded this anti-American stronghold early today in preparation for a complex raid to retake control of the city and apprehend those responsible for last week's slayings of four U.S. security contractors. The highly anticipated action, dubbed Operation Valiant Resolve, was expected to be one of the biggest military offensives since the fall of Saddam Hussein's government a year ago. All roads leading to this city of 300,000 were cut off and barricaded with tanks and concertina wire. Working through the cold and windy desert night, under a large moon, Marines set up camps for...