Federal prosecutors here in the United States made significant breakthroughs in attempts to clean up corporate America, filing charges against the highest-ranking Enron executive yet and gaining a key witness in the case against Martha Stewart. Andrew Fastow, the former chief financial officer of Enron, surrendered to authorities early yesterday morning before being taken in handcuffs to a Houston court. He was charged with three counts of fraud, money laundering and conspiracy at the energy firm, which went bankrupt last year. He could face 45 years in prison. Enron was the first in a wave of corporate scandals that has shocked the United States.