WASHINGTON -- A federal grand jury indicted a top congressional ally of President Bill Clinton on 17 charges of corruption in office Tuesday.The charges against Dan Rostenkowski, chairman of the House of Representatives Ways and Means Committee, include mail fraud, wire fraud, tampering with a witness, concealing a material fact, embezzlement of public funds, and aiding and abetting a crime.As head of the committee which approves the government's budget, Rostenkowski is one of the most powerful figures in Washington and a key player in Clinton's attempt to establish a national health care system.Rostenkowski, a Democrat from Chicago, has been under investigation for two years. He was suspected of padding his payroll with employees who did no work and cashing in office stamps for personal gain.The indictment, a formal list of charges, came a day after Rostenkowski defiantly rejected a plea agreement and vowed to fight government allegations that he defrauded taxpayers of hundreds of thousands of dollars."I am confident that I will be vindicated," Rostenkowski said in a statement Monday.The indictment will force him to step aside as Ways and Means chairman.Rostenkowski's decision to fight the charges meant, under House rules, that he must give up his powerful chairmanship at a time the committee is playing a central role in the health care reform debate. But Rostenkowski, 66, will remain a member of the House, and of the Ways and Means Committee.He vowed to seek a 19th term even as he fights the charges.Fellow Democratic Representative Sam Gibbons is in line to take over the committee, among the most powerful in Congress because of its jurisdiction over taxes, Social Security and the financing of many other major programs.Grand jury proceedings usually are secret, but because of the plea negotiations, it was clear the government was ready to charge Rostenkowski if he did not reach an agreement with prosecutors. So Washington began assessing the impact of his departure as chairman even before the indictment was officially issued.Asked whether Rostenkowski's departure would hurt health care reform, Vice President Al Gore said, "No. There's a lot of momentum for health care.""He's been an important player on health care ... and certainly the members have made it clear they will continue to work with him, and that's true of the White House as well," Press Secretary Dee Dee Myers said Friday.