Webster Hubbell -- formerly the Clinton Administration's No. 3 official at the Justice Department -- agreed today to help the government's Whitewater prosecution in exchange for pleading guilty to limited charges stemming from his bilking his former law firm and clients out of nearly $400,000. The charges he admitted to -- mail fraud and tax evasion -- are both felonies and carry a maximum of 10 years in prison and $500,000 in fines. Hubbell's problems stem from allegations first brought by former colleagues at Little Rock's Rose Law Firm, where Hubbell and Hillary Rodham Clinton were partners before the 1992 presidential election. The allegations forced Hubbell to resign his Justice Department post in March. Starr probed Hubbell's case even though it is not directly related to the Clintons' Whitewater land venture -- something the president's attorney, David Kendall, quickly pointed out: "This matter simply does not concern the president, the first lady, or Whitewater Development Company in any way." But Hubbell may be asked by Starr if there was any political interference by the Clinton Administration in the investigation of the failure of a savings and loan owned by the Clintons' Whitewater business partner. At the least, the guilty plea is embarassing for the Clintons. The President considered Hubbell, a golfing buddy and former Little Rock Mayor, to be one of his closest friends.