When John Hinckley's chief defense lawyer, Vincent J. Fuller, steps up to the courtroom lectern to speak, his words sometimes come forth in a quick, gravelly bark that leaves his listeners at a loss. "What?" the court reporter implores, and Fuller slows down--a bit.

Fuller, 50, is a senior partner at the Washington law firm of Williams & Connolly, where defense work in high-visibility, high-priced criminal cases is a fine art. While some of the partners, notably Edward Bennett Williams, have taken on the task with great public flash, Fuller--until now--has remained quietly behind the scenes.

Williams was one of Fuller's teachers at Georgetown University Law School and Fuller joined the firm shortly after graduation in 1956. A short, compact man, the father of five children, Fuller bounds around the courthouse with a bulldog-like determination that he is said to apply to both life and work. He is a reformed smoker, who dares visitors to light up when they are in his office.

Fuller's cocounsel on the Hinckley case is Gregory B. Craig, 37, who attended Cambridge University in England before graduating from Yale Law School in 1972. As a student, his love was politics and he once debated Spiro T. Agnew, then vice president, on network television, and worked on Edmund Muskie's campaign for president, according to a friend.

Craig, whose boyish looks and open enthusiasm contrast with Fuller's reserved and formal demeanor, joined the Williams firm after law school but took about two years off at one point while his wife, Derry, studied graphic design at Yale. During that time, Craig worked at the federal public defender's office in Connecticut.

Two other Yale Law School graduates are working with Fuller and Craig on the Hinckley case, Lon S. Babby, 31, and Judith A. Miller, also 31. Both were editors of the law journal there and both members of the Phi Beta Kappa honor society. Miller clerked for the late Harold Leventhal, who was a member of the U.S. Court of Appeals in Washington, and for now-retired U.S. Supreme Court Justice Potter Stewart.