John W. Hinckley Jr., the drifter accused of shooting President Reagan outside the Washington Hilton last March 30, was transferred to the brig at Quantico Marine Base yesterday from the Federal Correctional Institute at Butner, N.C., where he had been undergoing mental examinations.

Hinckley, 26, in the custody of deputy U.S. marshals, was brought by Marine helicopter to Quantico, which is located in Prince William County. A Justice Department spokesman said he is being isolated from the general brig population there.

U.S. District Court Chief Judge William B. Bryant had committed Hinckley to Butner on April 2 to undergo tests to determine whether Hinckley is competent to stand trial and was responsible for his acts at the time of the shooting. Sources said yesterday that the decision was made to move Hinckley to Quantico, where he had been incarcerated immediately after the incident, because doctors from the U.S. Bureau of Prisons had completed their examinations. Those doctors have given the court a written report, which was placed under seal on July 31.

Doctors appointed by both the defense and the prosecution are continuing their examination of Hinckley in preparation for trial, according to informed sources..

Meanwhile, informed sources said, that federal prosecutors have issued subpoenas for network film recordings of campaign appearances by former president Carter in Nashville and Dayton, and of President Reagan's inauguration, in an attempt to determine whether Hinckley was present at those occasions.

There have been reports that some law enforcement officials believe that Hinckley may have been stalking both Carter and Reagan before Reagan was shot. In addition to Reagan, presidential press secretary James Brady, Washington police officer Thomas Delahanty and Secret Service agent Timothy McCarthy also were shot. All have recovered from their wounds with the exception of Brady, who is still undergoing treatment.